REGULATION APPARATUS FOR A CURRENT CONVERTER, CURRENT CONVERTER ARRANGEMENT AND METHOD FOR REGULATING A GRID COUPLED CURRENT CONVERTER

A method for regulating a grid-coupled current converter includes adjusting a control voltage for the current converter in dependence on an output voltage of the current converter. The method provides limiting a voltage deviation between the control voltage and the output voltage. In embodiments, the limitation of a control voltage indicator takes place in amplitude and angle, wherein control ranges for amplitude and/or angle are adjusted depending on the situation. In further embodiments, the limitation takes place in coordinates of coordinate axes that are orthogonal and rectilinear to each other. Further, in a method for regulating a current converter, when determining a control quantity, a potential difference of the output voltage and a reference potential of a bridge voltage of the current converter is considered. Alternatively or additionally, contribution of a voltage oscillation in an intermediate circuit to the bridge voltage is considered.

BACKGROUND OF THE INVENTION

Current converters are used for feeding electrical energy into energy grids. Here, power fed into the energy grid by the current converter is normally regulated with respect to quantities predetermined for the energy grid, such as frequency and voltage.

Grid-forming current converters are characterized in that the same provide an independent voltage indicator. This includes, on the one hand, that the grid-forming current converter does not depend on a grid-side voltage source for its own operation. Further, the provided voltage indicator has an inertia capability. This means the same does not follow grid-side variations at any speed but maintains its rotation position at first and synchronizes itself with the external voltage source according to an inertia constant. In that way, the grid-forming current converter provides instantaneous reserves to the grid when needed. This operating principle can be found in the well-known synchronous machine, in which the induced magnet wheel voltage is connected directly to the inertial rotor. In a similar way, in current converters, an inertial voltage indicator (with respect to angle and amplitude) can be imprinted by control technology. Different methods are known for this [3]. If, however, the inertia capability is too strong, the voltage indicators move too far away from each other in certain situations (for example, in case of a frequency event in the grid), such that a high current is driven via a coupling impedance. In current converters, this can quickly result in inadmissibly high currents.

Different methods are known to prevent the problem of overcurrents in grid-forming current converters. Some of them have been specifically developed and analyzed for a specific scenario (e.g., Fault-Ride-Through (FRT)).

One approach is to switch to current regulation, i.e., to bring the current converter into the current-regulated operation as soon as a current limit is exceeded. This means the current converter is regulated to a fixed current set value (see, e.g., [4]).

Another approach increases the impedance in a virtual manner to limit the flowing current to an acceptable degree, like in the not pre-published patent application with the application number DE 1102020200673.3. If too high voltage differences occur, the current can be limited by the virtually imprinted impedance. Here, it is possible to emulate the additional impedance constantly or only when an event occurs. In constant usage, the current response (for example in case of a short circuit) depends on the operating point prior to the event. Additionally, the same cannot be selected to be too large as the same can limit the normal operation. This can again have the effect that the current is not sufficiently limited in the case of deep drops. This is aggravated by the fact that this approach cannot easily limit voltage differences relating to the voltage angle in the stationary state since the grid-forming regulation has integrated the angle in advance in order to approach the respective operating point.

Further examples for current limitation methods are described in [1] and [2], which can also be implemented in embodiments of the present invention.

SUMMARY

An embodiment may have a regulation apparatus for a current converter, wherein the regulation apparatus is configured to determine a control voltage for the current converter in dependence on an output voltage of the current converter, wherein the regulation apparatus is configured to limit an amplitude of a control voltage indicator describing the control voltage to an amplitude control range around an amplitude of a reference voltage indicator based on the output voltage, limit an angle of the control voltage indicator to an angle control range around an angle of the reference voltage indicator and adjust the amplitude control range and the angle control range depending on the situation.

Another embodiment may have a regulation apparatus for a current converter, wherein the regulation apparatus is configured to determine a control voltage for the current converter in dependence on an output voltage of the current converter, wherein the regulation apparatus is configured to limit a first coordinate of a control voltage indicator describing the control voltage to a first control range around a first coordinate of a reference voltage indicator based on the output voltage, limit a second coordinate of the control voltage indicator to a second control range around a second coordinate of the reference voltage indicator, wherein a first coordinate axis to which the first coordinates are related and a second coordinate axis to which the second coordinates are related are orthogonal and rectilinear to each other.

Another embodiment may have a regulation apparatus for a current converter, wherein the regulation apparatus is configured to determine a control quantity for the current converter, wherein the current converter includes an intermediate circuit, wherein the current converter is configured to provide a bridge voltage indicated by the control quantity based on the control quantity and an intermediate circuit voltage of the intermediate circuit at a circuit node coupled to a terminal point of the current converter via an internal impedance of the current converter, wherein the regulation apparatus is configured to, for the reference voltage indicator, consider a contribution of a least one voltage oscillation in the intermediate circuit to the bridge voltage and/or consider a potential difference between a reference potential of the bridge voltage and a reference potential of the output voltage.

According to another embodiment, a current converter arrangement may have: the inventive regulation apparatus, a current converter including a circuit node, wherein the current converter is configured to provide a voltage indicated by the control voltage at the circuit node, wherein the circuit node can be coupled to an energy grid via an internal impedance of the current converter.

According to another embodiment, a method for regulating a current converter may have the step of: determining a control voltage for the current converter in dependence on an output voltage of the current converter, determining the control voltage may have the steps of: limiting an amplitude of a control voltage indicator describing the control voltage to an amplitude control range around an amplitude of a reference voltage indicator based on the output voltage, limiting an angle of the control voltage indicator to an angle control range around an angle of the reference voltage indicator and adjusting the amplitude control range and the angle control range depending on the situation.

According to another embodiment, a method for regulating a current converter may have the step of: determining a control voltage for the current converter in dependence on an output voltage of the current converter, determining the control voltage may have the steps of: limiting a first coordinate of a control voltage indicator describing the control voltage to a first control range around a first coordinate of a reference voltage indicator based on the output voltage, limiting a second coordinate of the control voltage indicator to a second control range around a second coordinate of the reference voltage indicator, wherein a first coordinate axis to which the first coordinates are related and a second coordinate axis to which the second coordinates are related are orthogonal and rectilinear to each other.

According to another embodiment, a method for regulating a current converter may have the steps of: determining a control quantity for the current converter, providing a bridge voltage indicated by the control quantity at a circuit node coupled to a terminal point of the current converter via an internal impedance of the current converter, wherein providing takes place based on the control quantity and an intermediate circuit voltage of an intermediate circuit of the current converter, wherein the method may have, for determining the control quantity, considering a contribution of at least one voltage oscillation in the intermediate circuit to the bridge voltage and/or considering a potential difference between a reference potential of the bridge voltage and a reference potential of the output voltage.

Embodiments of the present invention are based on the idea of limiting the current fed into a grid by a current converter by limiting a control voltage indicator of a control voltage for regulating the current converter to a range around a reference voltage indicator describing an output voltage of the current converter (e.g., a voltage at terminal point of the current converter to the grid). The inventors have found that the amount of the fed-in current is determined by a deviation between the reference voltage indicator and the control voltage indicator. By limiting the deviation between the control voltage indicator for the current converter and the reference voltage indicator, the fed-in current can be reliably limited. For example, by limiting the deviation to a maximum deviation, the output current can be limited to a maximum current strength, wherein the maximum deviation can be based on the maximum current strength and an internal impedance of the current converter. The limitation of the control range can take place by limiting respective control ranges for coordinates of the control voltage indicator. For example, the control range can be limited via a limitation for an amplitude and an angle (i.e., phase angle) of the control voltage indicator, i.e., the same can be determined in polar coordinates. Alternatively, the control range can be limited via a respective limitation of two coordinates of a rectangular coordinate system.

Within the control range around the reference voltage indicator, to which the control voltage indicator is limited, the inventive concept can allow guiding the control voltage indicator by means of regulator dynamics, for example grid-forming regulator dynamics. Even in the limiting case, the control voltage indicator can still be regulated within the limited range, such that the regulation can still react to a new situation in the sense of the regulator dynamic, e.g., in a grid-compatible manner. Thus, even in the limiting case, the concept allows regulating the current converter in a voltage-controlled manner and to still feed current into the grid. Grid-forming characteristics of the regulation can therefore also be maintained in the limiting case such as in voltage or frequency failures in the grid and can be presented in a targeted manner up to a limiting value.

In contrast to the above-described approach of switching to current regulation in the case of overcurrent, in the inventive regulation, the inherently grid-compatible operating principle is not lost. At the same time, the inventive regulation provides an effective protection against overcurrent. In the regulation principle disclosed herein, in contrary to switching to current regulation, the regulation does not have to be interrupted even in case of failure. Thus, in particular in the case of a frequency event, the problem of when and in what way the current regulation is to be left again does not arise.

Embodiments of the present invention provide a regulation apparatus for a current converter, e.g., a grid-forming current converter. The regulation apparatus is configured to determine a control voltage for the current converter in dependence on an output voltage of the current converter. Further, the regulation apparatus is configured to limit an amplitude of a control voltage indicator describing the control voltage to an amplitude control range around an amplitude of a reference voltage indicator describing the output voltage. For example, the regulation apparatus receives a set control voltage indicator determined according to regulation criteria, e.g., by a control quantity regulation, wherein the set control voltage indicator represents, for example, a voltage indicator desired with respect to the regulation of the output voltage of the current converter to one or several set values (e.g., for one or several of amplitude, frequency, phase angle) and determines the control voltage indicator based on the set control voltage indicator by limiting amplitude and angle. As far as not described to the contrary, the control voltage indicator indicates the limited control voltage indicator whose amplitude and angle are limited to the respective control ranges. Further, the regulation apparatus is configured to limit an angle of the control voltage indicator to an angle control range around an angle of the reference voltage indicator. The regulation apparatus is configured to adjust the amplitude control range and/or the angle control range depending on the situation, i.e., to adjust, for example, a respective quantity of the amplitude control range and/or the angle control range depending on the situation and/or to adjust a respective position of the amplitude control range and/or the angle control range relative to the reference voltage indicator depending on the situation. For example, the regulation apparatus can determine or obtain the amplitude and the angle of the reference voltage indicator based on a measurement quantity describing the output voltage.

By limiting the amplitude of the control voltage indicator to the amplitude control range and limiting the angle of the control voltage indicator to the angle control range, reliable limitation of the deviation of the control voltage indicator from the reference voltage indicator is obtained. Further, the component-by-component limitation of the control voltage indicator allows prioritization of one of the components of amplitude and angle. When a limiting value is given for the current of the current converter, the freedom of movement in amplitude can be weighted against the freedom of movement in angle. Thus, adaptation to the application case or a current regulation situation is enabled.

For example, situation-dependent adjustment of the amplitude control range and the angle control range can be performed in dependence on an operating state of the current converter or the grid coupled to the current converter. Thereby, in different situations, a different component or coordinate, i.e., according to this embodiment, amplitude or angle can be prioritized. Thus, it is possible to prefer the regulation of the angle or the regulation of the amplitude, depending on the operating situation. In examples, the active component of the output current can be adjusted via the angle of the control voltage indicator, while in particular the reactive component can be adjusted via the amplitude. Therefore, the situation-dependent adjustment of the amplitude control range and the angle control range allows prioritizing the reactive power or the active power in the regulation in different situations in a different manner and/or to a different degree.

For example, the regulation apparatus can limit the control voltage indicator such that a deviation of the control voltage indicator from the reference voltage indicator does not exceed a maximum deviation, wherein the deviation can consider an amplitude deviation, i.e., a deviation of the amplitudes of the two voltage indicators and an angle deviation, i.e., a deviation of the angles of the two voltage indicators. For example, the regulating apparatus can adjust the amplitude control range and the angle control range such that, with full utilization of the respective control ranges, for example in a control voltage indicator which is both at the limit of the amplitude control range as well as the limit of the angle control range, the maximum deviation is not exceeded. In these examples, the regulation apparatus can adjust depending on the situation in what proportion the maximum deviation is divided to the respective control ranges of the coordinates amplitude and angle in order to prioritize one of the coordinates.

Alternatively or additionally, the regulation apparatus can adjust the amplitude control range and/or the angle control range depending on the situation, such that one of the control ranges for one of the coordinates is adjusted in dependence on an actual deviation, i.e., actually used deviation in the other coordinate. For this, for example, the limited control voltage indicator of the current clock or a previous clock (e.g., by assuming a slow change of the control voltage indicator) can be used. Thus, one of the coordinates can be prioritized and the control range for the other coordinate can be selected to be particularly large by considering the actually existing deviation, such that the maximum allowable deviation of the control voltage indicator from the reference voltage indicator can be utilized particularly well. For example, the inventors have found that, at a small angle deviation, the fed-in current is within the limits even in a greater amplitude control range.

According to embodiments, the regulation apparatus is configured to determine an upper and a lower limit of the amplitude control range based on a first deviation limiting value and the amplitude of the reference voltage indicator and to determine an upper and a lower limit of the angle control range based on a second deviation limiting value and the angle of the reference voltage indicator. For example, the first deviation limiting value can represent a limiting value for a deviation of the control voltage indicator from the reference voltage indicator in a first direction and the second deviation limiting value can represent a limiting value for a deviation of the control voltage indicator from the reference voltage indicator in a second direction. The first and the second direction can be directions in a coordinate system in which the control voltage indicator is described, wherein these directions do not necessarily have to correspond to the directions of the coordinate axes. For example, the first and second directions can be orthogonal to each other. In examples, the first direction can be a direction parallel to the reference voltage indicator and the second direction can be a direction orthogonal to the reference voltage indicator. The first direction can also be described as vertical direction and the second direction can be described as horizontal direction. Further, it should be noted that the upper and the lower limit of the respective control ranges do not have to be necessarily arranged symmetrically around the respective coordinate of the reference voltage indicator, in particular in the case of the amplitude control range. Thus, the amplitude control range and the angle control range can describe a range of any shape, in particular also a rectangle, even when the control voltage indicator is in polar coordinates (i.e., amplitude and angle). According to these embodiments, the regulation apparatus is configured to adjust the first deviation limiting value and the second deviation limiting value in dependence on each other, for example, the first and second deviation limiting values are determined in a correlated manner, e.g., based on a common input quantity, or one of the first and second deviation limiting values is determined based on the other one in order to limit a deviation of the control voltage indicator from the reference voltage indicator, for example to limit the same to a maximum deviation. Because the first and second deviation limiting values are determined in dependence on each other, it can be obtained that the deviation of the control voltage indicator from the reference voltage indicator does not exceed a maximum deviation by considering both coordinates and hence the output current does not exceed a maximum current strength.

In other words, these embodiments are based on the finding that considering their actually adjusted control voltage indicator for determining the amplitude control range and/or the angle control range allows selecting the amplitude control range or the angle control range to be as large as possible with respect to a given limiting current. For example, in the case of a small deviation of the control voltage indicator from the reference voltage indicator, in the one coordinate, the limiting value for the other coordinate can be selected to be higher and the current limit can still be maintained. This means in the case that in one component the deviation between control voltage indicator and reference voltage indicator is smaller than allowable according to the associated limiting value, the limiting value for the deviation of the other component can be adjusted such that according to the actual deviation of the control voltage indicator from the reference voltage indicator in the one component, the current limitation is also ensured for the other component, even in the limiting case.

According to embodiments, the regulation apparatus is configured to adjust, at least in a first operating situation, for example normal operation, one or several operating situations of the current converter, the angle control range to a predetermined angle control range, e.g., to a predetermined angle control range around the current reference voltage indicator. For example, the regulation apparatus uses a predetermined value for the second deviation limiting value to determine an upper and a lower limit of the angle control range with respect to the reference voltage indicator. Further, the regulation apparatus is configured to determine the amplitude control range in dependence on an angle deviation of the control voltage indicator (e.g., the limited control voltage indicator) from the reference voltage indicator. Here, the regulation apparatus can use, for example, the angle of the control voltage indicator limited to the angle control range determined for the current clock, or the angle of the limited control voltage indicator of a previous clock. Because the angle control range is predetermined, a minimum size of the angle control range is ensured, i.e., the angle (or a direction transversal to the reference voltage indicator or horizontal direction) is prioritized. Depending on the actual angle deviation, the amplitude control range can then be selected such that even with complete utilization of the amplitude control range, the maximum deviation of the control voltage indicator from the reference voltage indicator is not exceeded. Determining the amplitude control range in dependence on the angle deviation therefore allows, on the one hand, reliably limiting the current to a limiting value and, on the other hand, keeping the range by which the control voltage indicator can be regulated as large as possible.

In other words, by adjusting the angle control range to the predetermined value, regulation of the angle or the horizontal voltage component in a range determined by the predetermined value is ensured, and hence the regulation of the angle or the horizontal component of the control voltage indicator is preferred. This can be advantageous in situations where the regulation of the active component of the output current is to be prioritized. Further, these embodiments show the above-described advantages of considering the actual angle deviation of the control voltage indicator from the reference voltage indicator.

According to embodiments, the regulation apparatus is configured to adjust, in a second operating situation of the current converter, for example during a voltage drop of the output voltage, the amplitude control range to a predetermined amplitude control range, e.g., to a predetermined amplitude control range around the current reference voltage indicator. For example, the regulation apparatus uses a predetermined value for the first deviation limiting value to determine an upper and a lower limit of the amplitude control range with respect to the reference voltage indicator. Further, the regulation apparatus is configured to determine the angle control range in dependence on an amplitude deviation of the control voltage indicator from the reference voltage indicator. According to the description of the previous embodiment, in a second operation situation, instead of the angle or a transversal component (transversal to the reference voltage indicator), the amplitude or a longitudinal component (along the reference voltage indicator) is prioritized. Preferring the regulation of the amplitude or longitudinal component of the control voltage indicator can be advantageous in situations where the regulation of the reactive component of the output current is to be prioritized, for example in the case of a voltage drop.

According to embodiments, the regulation apparatus is configured to determine an upper and a lower limit of the amplitude control range based on a first deviation limiting value and the amplitude of the reference voltage indicator and to determine an upper and a lower limit of the angle control range based on a second deviation limiting value and the angle of the reference voltage indicator. Here, the above description of the lower and upper limits as well as the first and second deviation limiting values can apply. According to this embodiment, the regulation apparatus is configured to adjust, at least in a first operating situation of the current converter, e.g., a normal situation, the first deviation limiting value and the second deviation limiting value to a respective first predetermined value and to adjust, in a second operating situation of the current converter, the first deviation limiting value and the second deviation limiting value to a respective second value, wherein the respective first value differs from the respective second value. For example, depending on the situation, one of the two limiting values can be fixed to a predetermined value and the respective other of the two limiting values can be determined, for example calculated, according to the limiting current strength. These embodiments offer the advantage that the limiting values can be determined depending on the situation and the prioritization degree can be adjusted and/or the prioritized coordinate can be selected, for example, depending on the operating situation.

According to embodiments, the regulation apparatus is configured to determine the angle control range (e.g., the above-mentioned upper and lower limit of the angle control range) in dependence on the amplitude of the control voltage indicator and/or in dependence on the amplitude of the reference voltage indicator. Alternatively or additionally, the regulation apparatus is configured to determine the amplitude control range (e.g., the above-mentioned lower and upper limit of the amplitude control range) in dependence on an angle deviation of the control voltage indicator from the reference voltage indicator. Considering the angle or the amplitude allows a correction of a distortion of the control range as it can occur by the usage of polar coordinates. For example, determining the respective control ranges independent of amplitude and angle of the control voltage indicator or reference voltage indicator when using polar coordinates for determining the control range, can have the effect that the control range describes a circular ring segment in a polar coordinate system. Considering the amplitude of the control voltage indicator or reference voltage indicator effectively allows, for example, a limitation of the control range in transversal direction (e.g., horizontal direction) such that a constant control range in transverse direction is obtained, independent of the amplitude. Considering the angle of the control voltage indicator or reference voltage indicator effectively allows, for example, a limitation of the control range in longitudinal direction (e.g., vertical direction) such that the control range in longitudinal direction, considered in a rectangular coordinate system, is independent of the deviation in transversal direction. When considering amplitude and angle, for example, it can be obtained that by assuming a sufficiently slow change of the control voltage indicator or reference voltage indicator, the control range effectively available for the control voltage indicator describes a rectangle. As the control voltage indicator and the reference voltage indicator can be connected for determining the respective control ranges, e.g., via the first or second deviation limiting value, either the control voltage indicator or the reference voltage indicator can be used, wherein, e.g., the indicator of a previous clock can be considered.

According to embodiments, the regulation apparatus is configured to determine an upper and a lower limit of the amplitude control range based on a first deviation limiting value and the amplitude of the reference voltage indicator. Here, the above description of the lower and upper limits as well as of the first deviation limiting value can apply. As described, determining the lower and the upper limit allows asymmetrical positioning of the limits with respect to the amplitude of the reference voltage indicator, for example in dependence on the angle of the control voltage indicator. Therefore, this embodiment is particularly advantageous in combination with determining the amplitude control range in dependence on the angle deviation.

According to embodiments, the regulation apparatus is configured to determine an upper and a lower limit of the angle control range based on the angle of the reference voltage indicator and based on a ratio between a second deviation limiting value and the amplitude of the control voltage indicator or the reference voltage indicator. Here, the above description of the lower and upper limits as well as the second deviation limiting value can apply. As described, determining the lower and the upper limit allows positioning the limits with respect to the angle of the reference voltage indicator in dependence on the amplitude of the control voltage indicator. Thus, this embodiment is particularly advantageous in combination with determining the angle control range in dependence on the amplitude. Here, the usage of the ratio between the voltage deviation limiting value and the amplitude of the control voltage indicator or the reference voltage indicator allows a good tradeoff between a very exact correction of the stated distortion and little computing effort.

According to embodiments, the regulation apparatus is configured to determine the upper and the lower limit of the angle control range by means of a trigonometrical function in dependence on the ratio between the second deviation limiting value and the amplitude of the control voltage indicator or the reference voltage indicator. The trigonometrical function allows a compensation of the above-described distortions when using polar coordinates and hence a very exact determination of the control range, in particular in the case of large amplitude deviations.

According to embodiments, the regulation apparatus is configured to limit the angle of the control voltage indicator further with respect to a change compared to the angle of the reference voltage indicator or the control voltage indicator of an earlier clock. Thereby, a drift of the frequency of the voltage from a defined tolerance range can be prevented.

According to embodiments, the regulation apparatus is configured to determine a set control voltage based on a comparison of one or several measurement quantities describing an output power of the current converter (e.g., the output voltage and the output current) with one or several set values for the measurement quantities. The regulation apparatus is configured to limit an amplitude of a set control voltage indicator of the set control voltage to the amplitude control range and to limit an angle of the set control voltage indicator to the angle control range to determine the control voltage indicator. Further, the regulation apparatus is configured to determine the amplitude of the set control voltage indicator based on a difference of a measurement quantity (e.g., Q) describing a reactive power of an output power of the current converter and a set value for the reactive power. Further, the regulation apparatus is configured to determine the angle of the set control voltage indicator based on a difference of a measurement quantity describing an active power of an output power of the current converter and a set value for the active power and based on a difference of the amplitude of the set control voltage indicator and a set value for an amplitude of the output voltage of the current converter. Considering the difference of the amplitude of the set control voltage indicator and the set value for the amplitude for determining the angle of the set control voltage indicator can allow a good dynamic reaction in regulating the control voltage, in particular in the case of a resistive grid.

Further embodiments of the present invention provide a regulation apparatus for a current converter, e.g., a grid-forming current converter. The regulation apparatus is configured to determine a control voltage for the current converter in dependence on an output voltage of the current converter. For this, the regulation apparatus is configured to limit a first coordinate of a control voltage indicator describing the control voltage to a first control range around a first coordinate of a reference voltage indicator based on the output voltage and to limit a second coordinate of the control voltage indicator to a second control range around a second coordinate of the reference voltage indicator. The first coordinate axis to which the first coordinates relate, i.e., the first coordinate of the control voltage indicator and the first coordinate of the reference voltage indicator, and a second coordinate axis to which the second coordinates are related are orthogonal and rectilinear to each other. For example, the first and second coordinate axis are orthogonal to each other, but not curvilinear orthogonal to each other, i.e., orthogonal rectilinear. For example, the first and the second coordinate are related to two coordinate axes of a Cartesian coordinate system.

The inventors have found that the usage of a Cartesian coordinate system offers the advantage that the control ranges can be determined very easily, i.e., with little computing effort and at the same time with high accuracy, i.e., that a range determined by a maximum output current can at the same time be maintained and well utilized. In particular, the above-described distortions that can occur when using polar coordinates are prevented. For example, rectangular or circular control ranges for the control voltage indicator can be determined in a very easy manner.

As described above with respect to the previous embodiments, as long as not described to the contrary, the control voltage indicator refers to the limited control voltage indicator whose coordinates are limited to the respective control ranges. Also according to these embodiments, the regulation apparatus can obtain a set control voltage indicator and determine the control voltage indicator based on the set control voltage indicator.

For example, these embodiments can differ from the ones described above in that instead of the amplitude control range and the angle control range, the first and second control ranges, which are determined in an orthogonal coordinate system, are used for the limitation. According to these embodiments, the control voltage indicator is described in a rectangular coordinate system. Further, optionally, these embodiments can differ from the ones described above in that the first and second control ranges are not necessarily determined according to this situation, which can be, however, the case according to embodiments. Apart from these differences, the above-described embodiments can optionally also be combined with these further embodiments, wherein, for example, the first coordinate replaces the amplitude, the second coordinate replaces the angle, the first control range replaces the amplitude control range and the second control range replaces the angle control range. Thus, in examples, the first coordinate can describe a longitudinal component or vertical component and the second coordinate can describe a transversal component or horizontal component. In particular, in this sense, the regulation apparatus can determine the first control range and the second control range as described in dependence on each other and/or the described situation-dependent determination can be implemented.

According to embodiments, the regulation apparatus is configured to limit a deviation of the first coordinate of the control voltage indicator from the first coordinate of the reference voltage indicator to a first deviation limiting value. Further, the regulation apparatus is configured to limit a deviation of the second coordinate of the control voltage indicator from the second coordinate of the reference voltage indicator to a second deviation limiting value. The first and second deviation limiting values can, for example, represent limiting values for an amount of a deviation of the control voltage indicator from the reference voltage indicator. For example, the first and second deviation limiting values are based on an internal impedance of the current converter and a limiting current strength for an output current provided by the current converter (i.e., the fed-in current of the current converter). For example, based on the internal impedance and the limiting current strength, a voltage deviation limiting value can be determined, which can form the basis of an amount of a maximum deviation of the control voltage indicator from the reference voltage indicator. This can also apply to the first and second deviation limiting values according to the implementations with polar coordinates. In combination with the usage of an orthogonal coordinate system, this allows a simple implementation. In particular, simple determination of the deviation limiting values and hence the two control ranges in dependence on each other and/or a simple situation-dependent determination is enabled.

According to embodiments, the first coordinate axis is parallel to the reference voltage indicator and the second coordinate axis is orthogonal to the reference voltage indicator. Thus, the first control range can represent a limitation of the longitudinal component or horizontal component of the control voltage indicator and the second control range can represent a limitation of the transversal component or vertical component of the control voltage indicator. A deviation of the control voltage indicator from the reference voltage indicator in a parallel direction can, for example, be particularly well suited for regulation of the reactive power of the current converter, and a deviation of the control voltage indicator from the reference voltage indicator in an orthogonal direction can, for example, be particularly well suited for regulating the active power. By selecting this coordinate system, the parallel and the orthogonal component can be considered separately or independent of each other and a dependency between the coordinates can be easily implemented.

According to embodiments, the first control range and the second control range describe a control voltage indicator control range limited by parallel lines to the first coordinate axis and parallel lines to the second coordinate axis.

According to embodiments, the regulation apparatus is configured to adjust the first control range and the second control range depending on the situation. As described, the situation-dependent determination of the control ranges described with respect to the above embodiments can also be implemented in the orthogonal coordinate system, with the above shown correspondences and the respective advantages.

According to embodiments, the regulation apparatus is configured to limit the first coordinate of the control voltage indicator further with respect to a change compared to the first coordinate of the reference voltage indicator or the control voltage indicator of an earlier clock. Alternatively or additionally, the regulation apparatus is configured to further limit the second coordinate of the control voltage indicator with respect to a change compared to the second coordinate of the reference voltage indicator or the control voltage indicator of an earlier clock. This embodiment has the same advantages as described above with respect to the limitation of the change of the angle.

According to embodiments, which can be implemented independent of the selection of the coordinate system, the current converter comprises an intermediate circuit and the current converter is configured to provide a bridge voltage indicated by the control voltage based on the control voltage and an intermediate circuit voltage of the intermediate circuit at a switching node coupled to a terminal point of the current converter via an internal impedance of the current converter. The regulation apparatus is configured to consider, for the reference voltage indicator, a contribution of at least a voltage oscillation in the intermediate circuit to the bridge voltage. Alternatively or additionally, the regulation apparatus is configured to consider a potential difference between reference potential of the bridge voltage and a reference potential of the output voltage. Considering one or both of these terms allows an exact limitation of the output current as described with respect to the following embodiments.

Further embodiments of the present invention provide a regulation apparatus. The regulation apparatus is configured to determine a control quantity for the current converter. The current converter comprises an intermediate circuit and is configured to provide, based on the control quantity and an intermediate circuit voltage of the intermediate circuit at a circuit node coupled to a terminal point of the current converter via an internal impedance of the control converter, a bridge voltage indicated by the control quantity. For example, the control quantity indicates a duty cycle for a pulse with modulation (PWM) of a half bridge providing the bridge voltage. The regulation apparatus is configured to consider, for the control quantity, a contribution of at least a voltage oscillation in the intermediate circuit to the bridge voltage. Alternatively or additionally, the regulation apparatus is configured to consider a potential difference between a reference potential of the bridge voltage and a reference potential of the output voltage. The reference potential of the output voltage is, for example, a neutral conductor or ground or earth.

The inventors have found that voltage oscillations can occur in the intermediate circuit, which can show in a contribution to the bridge voltage, in addition to an intended quantity of the bridge voltage that is indicated, for example, by the control voltage. This contribution can particularly be relevant for oscillations with the frequency of the fundamental oscillation of the bridge voltage or with the frequency of a multiple thereof. If this contribution is considered when determining the control quantity, for example by correcting or changing the control quantity accordingly, it can be ensured that the bridge voltage has the desired size. Thus, the accuracy of the current limitation can be increased.

Further, the inventors have found that the reference potential of the bridge voltage can differ from the reference potential of the output voltage. As the control quantity can be determined based on the output voltage, for example by the regulation apparatus, this potential difference can have the effect that an adjusted bridge voltage can differ by this potential difference from a voltage provided with a current converter regulation. For example, a current converter regulation for regulating the current converter can provide a specific ratio (e.g., in amplitude and phase angle) of the bridge voltage to the output voltage and the control quantity can be determined such that the bridge voltage is adjusted accordingly. The potential difference can have the effect that the resulting ratio between the bridge voltage and the output voltage does not correspond to the intended one. According to the invention, such an error can be prevented by considering the potential difference for the control quantity. This can also increase the accuracy of the current limitation.

According to embodiments, the voltage oscillation is a voltage oscillation between an intermediate circuit voltage supply and a reference potential of the intermediate circuit or alternatively a voltage oscillation between an intermediate circuit voltage supply and a further intermediate circuit voltage supply. The reference potential of the intermediate circuit can be, for example, an average value of the potentials of two or several intermediate circuit voltage supplies. For example, the intermediate circuit includes one or several capacitances connected in series between the intermediate circuit supplies. Thus, a voltage oscillation can occur between one of the intermediate circuit voltage supplies and the reference potential, even when the intermediate circuit voltage (for example a voltage between the intermediate circuit supplies) is constant. In examples, the reference potential of the intermediate circuit can correspond to the reference potential of the bridge voltage. In further examples, the reference potential of the bridge voltage can be actively regulated with respect to the intermediate circuit, e.g., by a half bridge provided for this purpose.

According to embodiments, a frequency of the voltage oscillation, i.e., the considered voltage oscillation, is one or several times a fundamental oscillation of the bridge voltage (or the output voltage). The inventors have found that a voltage oscillation with such a frequency can result in a relevant contribution to the bridge voltage. In examples, the regulation apparatus can consider the contributions of several voltage oscillations whose frequencies each are one or several times the fundamental oscillation.

According to embodiments, the reference potential of the bridge voltage depends on the potential of at least one intermediate circuit voltage supply. For example, the potential of the intermediate circuit voltage supplies can be floating with respect to the reference potential of the output voltage.

According to embodiments, the reference potential of the bridge voltage is determined by an average value of the potentials between which the intermediate circuit voltage is applied.

According to embodiments, the current converter is a multi-phase current converter and the current converter is configured to provide one bridge voltage each for each of a plurality of phases of the current converter at a respective circuit node coupled to a respective terminal point of the current converter via a respective internal impedance of the current converter. For example, the regulation apparatus according to these embodiments can determine one control quantity each for each of the phases, e.g., for regulating a respective half bridge providing the respective bridge voltage. Here, the regulation apparatus can consider the contribution of the voltage oscillation for each of the control quantities. Further, the regulating apparatus can consider, for each of the phases, the contribution of the potential difference between the reference potential of the intermediate circuit and the reference potential of the bridge voltages. The inventors have found that the voltage oscillations can generate a relevant contribution, in particular in the case of unbalanced regulated bridge voltages.

According to embodiments, the reference potential of the bridge voltage is based on a sum of the bridge voltages for the plurality of phases. For example, the reference potential is the sum of the bridge voltages or the average value of the bridge voltages. Alternatively, the reference potential of the bridge voltage can also be the sum of respective control voltages for the bridge voltages.

According to embodiments, the regulation apparatus is configured to determine a control voltage for the current converter in dependence on an output voltage of the current converter and to determine the control quantity based on the control voltage. For example, the control voltage can correspond to the control voltage as described with respect to the above embodiments. For example, the control voltage indicates the bridge voltage to be adjusted. According to these embodiments, the regulation apparatus is configured to consider the contribution of the voltage oscillations and/or the potential difference for determining the control voltage. For example, the regulation apparatus can correspond to one of the above described regulation apparatuses and the voltage oscillation and/or the potential difference can be considered when determining the reference voltage indicator and can hence be considered when limiting the control voltage indicator, such that the control voltage indicator can be limited in a particularly exact manner. Alternatively, the regulation apparatus can determine the control quantity based on the control voltage and additionally based on the contribution of the voltage oscillation and/or the potential difference. The latter alternative offers the advantage that the contributions are also considered in the regulation.

According to embodiments, the regulation apparatus corresponds to one of the regulation apparatuses described above that are configured to limit the control voltage indicator.

The following advantageous embodiments relate to all the above-described embodiments of the regulation apparatuses.

According to embodiments, the regulation apparatus is configured to determine a set control voltage based on a comparison of one or several quantities describing an output power of the current converter (e.g., one or several measurement quantities, e.g., out of output voltage, output current, reactive power, active power and one or several control quantities, e.g., frequency, amplitude) with one or several set values or nominal values for the quantities, and to supply the set control voltage to the limitation in order to determine the control voltage. This means the coordinates (e.g., amplitude/angle or first/second coordinate) of the set control voltage indicator are supplied to a limiting function to determine the coordinates of the control voltage indicator, such that the coordinates of the control voltage indicator are limited according to the limiting function. For example, the regulation apparatus can comprise a regulation, here also called current converter regulation, for example a grid-forming regulation and the determination of the set control voltage can take place according to the regulation of the regulation apparatus, for example according to a grid-forming regulation. In other words, the set control voltage can correspond to an unlimited control voltage that is determined according to a regulation of the current converter. Thus, within the amplitude control range and the angle control range, the amplitude and the angle of the control voltage can be regulated according to the regulation of the regulation apparatus, wherein, within the amplitude control range and the angle control range, the characteristics of the regulation can be used, for example grid-forming characteristics of a grid-forming regulation.

According to embodiments, the regulation apparatus is configured to limit a first coordinate of a set control voltage indicator of the set control voltage to a first control range and to limit a second coordinate of the set control voltage indicator to a second control range to determine the control voltage indicator. According to these embodiments, the regulation apparatus is configured to determine the first coordinate (42′) (e.g., the amplitude or the first of two coordinates that are orthogonal to each other) and the second coordinate (e.g., the angle or the second one of two coordinates that are orthogonal to each other) of the set control voltage indicator by using respective integrators. According to these embodiments, the regulation apparatus is configured to lead, in the case of a deviation of a first coordinate of the control voltage indicator from the first coordinate of the set control voltage indicator, an integrator input quantity of the integrator used for determining the first coordinate of the set control voltage indicator, to zero or to reinitialize the integrator used for the determination of the first coordinate of the set control voltage indicator. According to these embodiments, the regulation apparatus is further configured to lead, in the case of a deviation of a second coordinate of the control voltage indicator from the second coordinate of the set control voltage indicator, an integrator input quantity of the integrator used for determining the second coordinate of the set control voltage indicator, to zero or to reinitialize the integrator used for the determination of the second coordinate of the set control voltage indicator. Thereby, it can be prevented that the amplitude or the angle and the rotational speed of the control set voltage indicator drift off due to a limitation of the control voltage indicator.

According to embodiments, the current converter is a multi-phase current converter. Here, the reference voltage indicator describes a plurality of output voltages that are each allocated to a phase of a plurality of phases of the current converter. For example, the reference voltage indicator is a space indicator describing the plurality of output voltages. According to these embodiments, the current converter is configured to provide a voltage indicated by the control voltage for each of the phases. Therefore, the control voltage can allow regulation of several phases. Such a regulation can in particular be advantageous for balanced grids as the same may have a low implementation effort.

According to embodiments, the current converter is a multi-phase current converter and the regulation apparatus is configured to determine, for each of a plurality of phases of the current converter, one control voltage each in dependence on an output voltage of the respective phase. According to these embodiments, the regulation apparatus is configured to determine, for each of the phases, a control voltage indicator describing the respective control voltage and to limit the respective control voltage indicators to a control range, for each of the phases separately. For example, the regulation apparatus can determine a respective control range for each of the phases based on the output voltage of the respective phase, e.g., a respective control range around the respective reference voltage indicator. Here, the respective control ranges can be determined, for example, based on respective deviation limiting values or based on common deviation limiting values for all phases. Limiting the control voltage indicators separately is in particular advantageous to perform the limitation in the case of an unbalanced event in the grid adapted to the respective phase.

According to embodiments, the current converter is a three-phase current converter. Here, the current converter is configured to provide, depending on the control voltage, one voltage each for a first, second and third phase of the three-phase current converter. According to these embodiments, the regulation apparatus is configured to obtain a positive-phase sequence system reference voltage indicator, a negative-phase sequence system reference voltage indicator and a zero-phase sequence system reference voltage indicator, which commonly describe respective output voltages of the first, second and third phase. Here, the regulation apparatus is configured to limit a positive-phase sequence system control voltage indicator (32p) describing a positive-phase sequence system of the control voltage to a control range around the positive-phase sequence system reference voltage indicator. Further, the regulation apparatus in these embodiments is configured to limit a negative-phase sequence system control voltage indicator (32n) describing a negative-phase sequence system of the control voltage to a control range around the negative-phase sequence system reference voltage indicator. Further, the regulation apparatus in these embodiments is configured to limit a zero-phase sequence system control voltage indicator describing a zero-phase sequence system of the control voltage to a control range around the zero-phase sequence system reference voltage indicator. A separate limitation of the control voltage in positive-phase sequence system, negative-phase sequence system and zero-phase sequence system serves to limit the individual phase currents even in the case of an unbalanced event in the grid. By regulating the current converter in the positive-phase sequence system, negative-phase sequence system and zero-phase sequence system, the current converter can adjust its balance contribution.

According to embodiments, the current converter is configured to provide a bridge voltage indicated by the control voltage at a circuit node coupled to a terminal point of the current converter via an internal impedance of the current converter. For example, the current converter can be configured to be coupled to a grid at the terminal point.

Further embodiments of the present invention provide a current converter arrangement comprising the regulation apparatus according to any of the preceding embodiments and the current converter, wherein the current converter comprises the circuit node. Here, the current converter is configured to provide a voltage indicated by the control voltage at the circuit node. Further, the circuit node can be coupled to an energy grid via an internal impedance of the current converter.

Further embodiments provide a method for regulating a current converter. The method includes determining a control voltage for the current converter in dependence on an output voltage of the current converter, wherein determining the control voltage comprises a step of limiting an amplitude of a control voltage indicator describing the control voltage to an amplitude control range around an amplitude of a reference voltage indicator based on the output voltage. A step of limiting an angle of the control voltage indicator to an angle control range around an angle of the reference voltage indicator. Further, the method includes situation-dependent adjusting of the amplitude control range and the angle control range.

Further embodiments provide a method for regulating a current converter. The method includes determining a control voltage for the current converter in dependence on an output voltage of the current converter, wherein determining the control voltage comprises: a step of limiting a first coordinate of a control voltage indicator describing the control voltage to a first control range around a first coordinate of a reference voltage indicator based on the output voltage. A step of limiting a second coordinate of the control voltage indicator to a second control range around a second coordinate of the reference voltage indicator. Here, a first coordinate axis to which the first coordinates are related and a second coordinate axis to which the second coordinates are related are orthogonal to each other.

Further embodiments provide a method for regulating a current converter. The method includes a step of determining a control quantity for the current converter. Further, the method includes a step of providing a bridge voltage indicated by the control quantity to a circuit node coupled to a terminal point of the current converter via an internal impedance of the current converter. Providing the bridge voltage takes place based on the control quantity and an intermediate circuit voltage and an intermediate circuit of the current converter. Further, for determining the control quantity, the method includes considering a contribution of at least a voltage oscillation in the intermediate circuit to the bridge voltage and/or considering a potential difference between a reference potential of the bridge voltage and a reference potential of the output voltage.

Further embodiments provide a computer program having a program code for performing one of the methods described herein when the program runs on a computer or signal processor.

DETAILED DESCRIPTION OF THE INVENTION

In the following, examples of the present disclosure will be described in detail and by using the accompanying description. In the following description, many details are described for providing a thorough explanation of examples of the disclosure. However, it is obvious for a person skilled in the art that other examples can be implemented without these specific details. Features of the different described examples can be combined except when features of a respective combination exclude each other or such a combination is explicitly excluded.

It should be noted that the same or similar elements or elements having a similar functionality can be provided with the same or similar reference numbers or can be indicated in the same way, wherein a repeated description of elements provided with the same or similar reference numbers or that are indicated in the same way is typically omitted. Descriptions of elements that have the same or similar reference numbers or that are indicated in the same way are inter-exchangeable.

The following description begins with a description of a regulation apparatus in connection with a current converter according to embodiments of the invention. The regulation apparatus described with respect toFIG.1represents a frame in which embodiments of the invention can optionally be implemented. However, it should be noted that other embodiments can be implemented differently than in the frame shown inFIG.1.

It should be noted that optional elements and signals are illustrated in dotted lines as well as optional groupings of elements.

FIG.1illustrates a regulation apparatus10for a current converter80. The regulation apparatus10is configured to determine a control voltage32for the current converter80. The current converter80can be coupled to an energy grid8at a terminal point82. The regulation apparatus10can include a control quantity regulation20, which determines a set control voltage32′ based on one or several measurement quantities84. The measurement quantities84describe, for example, an output voltage and/or an output current of the current converter80, for example at the terminal point82. The current converter regulation20is, for example, a grid-forming regulation. Alternatively, the current converter regulation20can be implemented separately from the regulation apparatus10and can provide the set control voltage32′ for the same. The set control voltage32′ can represent, for example, information on a voltage to be adjusted by the current converter80.

The regulation apparatus10optionally includes a limiting module30that receives the set control voltage and determines a control voltage32that is limited to a control range around a reference voltage indicator60. In this case, the control voltage32or information derived therefrom, e.g., a control quantity, is passed on to the current converter. The reference voltage indicator60describes the output voltage of the current converter. The reference voltage indicator60can be determined by a reference voltage indicator determination module78based on one or several of the measurement quantities84. For example, the reference voltage indicator60can be determined based on a time course of a measurement quantity describing the output voltage. In examples, the reference voltage indicator is determined independent of the output current of the current converter.

The set control voltage and the control voltage can be represented based on voltage indicators that are described, in several, for example two, coordinates. The coordinates can relate, for example, to a polar coordinate system in which a voltage indicator can be described in amplitude and angle (phase angle). Alternatively, a voltage indicator can be described in a Cartesian or orthogonal coordinate system in which the coordinates can express, for example, a real and imaginary part of the voltage indicator. The set control voltage indicator32′ and the control voltage indicator32can be described independent of each other in one of these coordinate systems, i.e., optionally, conversion can be performed prior and/or after the limitation30. The set control voltage indicator32′ and the control voltage indicator32can also exist in the same coordinate system.

The regulation apparatus10can be implemented separately of the current converter80and can provide the control voltage32for the current converter80. Alternatively, the regulation apparatus10can also be part of the current converter80, completely or partly. For example, the regulation apparatus can be a computer or a signal processor or can include one or several thereof, and the described modules of the regulation apparatus can be part of a software executed thereon.

Embodiments of the present invention include a current converter arrangement2, which comprises the regulation apparatus10and the current converter80. The regulation apparatus10can provide the control voltage32, for example in the form of information or a signal for the current converter.

FIG.2illustrates a regulation apparatus110for the current converter80according to an embodiment. Optionally, the regulation apparatus110can correspond to the regulation apparatus10and can optionally comprise the features described with respect toFIG.1. The regulation apparatus110is configured to determine a control voltage32for the current converter in dependence on the output voltage of the current converter80. The regulation apparatus110comprises an amplitude limiting module41that is configured to limit an amplitude42of a control voltage indicator describing the control voltage32to an amplitude control range44around an amplitude62of a reference voltage indicator60describing the output voltage. For example, the reference voltage indicator60represents information on the output voltage. The regulation apparatus110comprises an amplitude control range determination module43that is configured to determine the amplitude control range44. Further, the regulation apparatus110includes an angle limiting module51that is configured to limit an angle52of the control voltage indicator32to an angle control range54around an angle64of the reference voltage indicator60. The regulation apparatus110comprises an angle control range determination module53that is configured to determine the angle control range54. The regulation apparatus110is configured to determine the amplitude control range44and the angle control range54depending on the situation.

The amplitude limiting module41receives, as input quantity, an amplitude42′ of an unlimited control voltage indicator32′, which is also referred to as set control voltage indicator32′. The amplitude limiting module41can provide, for example, the amplitude42′ as the amplitude42when the amplitude42′ is within the amplitude control range44and can otherwise limit the amplitude42′ to the amplitude control range44to obtain the amplitude42. Accordingly, the angle limiting module51can obtain an angle52′ of the set control voltage indicator32′. For example, the angle limiting module51can provide the angle52′ as the angle52when the angle52′ is within the angle control range54and can otherwise limit the angle52′ to the angle control range54to obtain the angle52.

An output current fed into the grid8by the current converter80(for example a current at the terminal point82) can depend on a deviation between the control voltage indicator and the reference voltage indicator or can be determined by the same. By limiting of the control voltage indicator32, it can be ensured that the control voltage indicator can deviate from the reference voltage indicator60within the amplitude control range44and the angle control range54and a limiting current strength for the output current is still maintained.

A situation depending on which the amplitude control range44and the angle control range54can be determined can result, for example, from the operating state of the current converter80or from the output voltage and/or the output current of the current converter80, for example, from a time course of the output voltage and/or the output current at the terminal point82. For example, in the case of a voltage drop, a frequency event or another failure, determining the amplitude control range44and the angle control range54can take place differently compared to a normal situation without any failure.

For example, depending on the situation, a selection of a prioritized coordinate or component of the amplitude and the angle of the control voltage indicator32can be made. For example, in a first operating situation of one or several operating situations of the current converter, the angle control range54is set to a predetermined range. In this case, the amplitude control range44can be determined in dependence on the actual angle deviation of the control voltage indictor32from the reference voltage indicator60. Here, the limited angle of the control voltage indicator of the current clock can be considered or, in order to prevent an algebraic loop, the angle of an earlier clock.

For example, in a second operating situation of the current converter, for example during a failure, the amplitude control range44can be set to a predetermined range. In this case, the angle control range54can be determined in dependence on the actual amplitude deviation of the voltage indicator32from the reference voltage indicator60. Here, the limited amplitude of the control voltage indicator of the current clock can be considered or, in order to prevent an algebraic loop, the amplitude of an earlier clock.

In further examples, the amplitude control range44and the angle control range54can be determined in dependence on each other, i.e., in a correlated manner, e.g., such that deviation of the control voltage indicator32from the reference voltage indicator60does not exceed a maximum deviation, e.g., even not when the control voltage indicator32is at the limits of both control ranges. In this case, depending on the situation, the size of the two control ranges can be adjusted, for example, depending on the situation, a ratio of the sizes of the two ranges can be set.

According to embodiments, the regulation apparatus110is configured to determine the amplitude62and the angle64of the reference voltage indicator based on a measurement quantity describing the output voltage, for example U0, which can be part of the measurement quantities84. For this, the regulation apparatus110can comprise a reference voltage indicator determination module78.

The amplitude42′ and the angle52′ of the unlimited control voltage indicator can be determined by a control quantity regulation20. The control quantity regulation20can be part of the regulation apparatus110as exemplarily illustrated inFIG.1. Alternatively, the control quantity regulation20can be implemented separately from the regulation apparatus110and the regulation apparatus110can receive the unlimited control voltage indicator from the control quantity regulation20. The one or several measurement quantities84can describe a voltage U0and a current I0at the terminal point82. The control quantity regulation20can determine the amplitude42′ and the angle52′ of the set control voltage indicator based on the one or several measurement quantities84. For this, the control quantity regulation20can compare one or several measurement quantities with their respectively associated set values and determine the set control voltage indicator based on the comparison. For example, based on the measurement quantities84, the control quantity regulation22can determine one or several of measurement quantities describing an output power of the current converter. The output power of the current converter can be, for example, a power fed into the grid8at the terminal point82by the current converter80. Based on a current measured at the terminal point82and a voltage measured at the terminal point82, the control quantity regulation20can determine an active power P and a reactive power Q.

According to embodiments, the control quantity regulation is configured to determine, based on a comparison of one or several measurement quantities, e.g., P, Q, describing an output power of the current converter, with one or several set values or nominal values for the measurement quantities, a set control voltage, which is described, for example, by the set control voltage indicator with amplitude42′ and angle52′. The amplitude42′ and the angle52′ are input quantities for the amplitude limiting module41and the angle limiting module51determining the amplitude42and the angle52based thereon.

FIG.3illustrates a further embodiment of the regulation apparatus110. According to the embodiment ofFIG.3, the regulation apparatus110comprises a first deviation limiting value determination module45that is configured to determine the one first deviation limiting value46and to provide the same for the amplitude control range determination module43. The regulation apparatus110according toFIG.3further includes a second deviation limiting value determination module55that is configured to determine a second deviation limiting value56and provide the same to the angle control range determination module53.

The first and second deviation limiting values can indicate respective values for a maximum deviation in a first and a second direction from the reference voltage indicator60as will be described below in more detail with reference toFIG.4B.

In examples where the first deviation limiting value46and the second deviation limiting value56are determined separately, as can be the case, e.g., in the case of the rectangular areas ofFIG.4B, the first deviation limiting value46and the second deviation limiting value56can be determined depending on the situation, such that weighting between the first and second deviation limiting value56is adjusted depending on the situation.

FIG.4Ashows an equivalent circuit diagram of an example of the current converter80. The equivalent circuit diagram illustrates the current converter80as equivalent two-pole. According toFIG.4A, the current converter80is configured to provide a bridge voltage Uiindicated by the control voltage32at a circuit node80coupled to the terminal point82of the current converter80via an internal impedance86of the current converter80.

For example, the internal impedance86can be a filter impedance or part of a filter impedance, for example of a sinusoidal filter. The current converter80provides the bridge voltage Uiat the circuit node88based on the control voltage32provided by the regulation apparatus10. As indicated inFIG.4A, the output voltage applied to the terminal point82can be described by the reference voltage indicator60. It should be noted that the terminal point82describes a point where the output voltage is measured. The terminal point82can be selected differently, as long as the internal impedance86describes the impedance between the circuit node88and the terminal point82. For example, the capacitor voltage (e.g., as output voltage) can be measured or another voltage of the current converter or the grid connection. In this case, the internal impedance also has to be adapted accordingly. Therefore, the bridge voltage88provided by the current converter80based on the control voltage32is therefore connected to the output voltage measured at the terminal point82via the internal impedance86.

Further, it should be noted that underlined quantities such as Ui, U0, and Z1inFIG.4Acan be vectorial quantities that are described, for example, by complex indicators. These indicators can described a time course or a frequency dependency of the respective quantities, for example, by means of an amplitude in an (phase) angle. For example, the internal impedance Zi can be frequency dependent.

A current fed into the grid8by the current converter80, i.e., an output current provided by the current converter80depends, according toFIG.4A, on a difference between the bridge voltage Uiand the output voltage U0as well as on the internal impedance86. For example, a product of the output current and the internal impedance86can correspond to the difference between Uiand U0.

Accordingly, according to embodiments, the first and second deviation limiting value46,56are determined based on the internal impedance86of the current converter and a limiting current strength Imaxfor an output current provided by the current converter. For example, based on the limiting current strength and the internal impedance86, a voltage deviation limiting value can be determined that can be used for determining the first and/or the second deviation limiting value46,56. The voltage deviation limiting value can be an indicator for a maximum deviation of the controlled voltage indicator Uifrom the output voltage indicator U0, cf.FIG.4B.

Therefore, according to the invention, the output current of the current converter80can be limited in that a difference between the bridge voltage Uiand the output voltage U0is limited as will be described below with reference toFIG.4B. As the bridge voltage Uican depend directly on the control voltage32, which indicates the bridge voltage to be set by the current converter80, a limitation of the control voltage32can effect a limitation of the bridge voltage. Accordingly, a limitation of the control voltage32can mean to limit the control voltage32such that the bridge voltage indicated by the control voltage32is limited as described.

The controlled voltage indicator Uidescribes the bridge voltage provided at the circuit node88and is indicated by the control voltage indicator32. This means the control voltage indicator32can represent information (or a signal) based on which the current converter80provides the bridge voltage. The control voltage indicator32can correspond to the controlled voltage indicator Ui. Alternatively, the control voltage indicator32can differ from the controlled voltage indicator Uiand can be connected to the same, for example, via one or several scaling factors and one or several offset factors or correction terms. These factors can be considered when limiting the control voltage indicator32(cf. correction terms71,72inFIG.5). The ratio between the control voltage indicator32and the controlled voltage indicator Ui(i.e., for example an offset or a scaling) can again be considered when determining and/or limiting the control voltage indicator32, by considering the ratio when determining the reference voltage indictor60based on the output voltage U0. In other words, considering the deviation from the controlled voltage indicator Uifrom the output voltage indicator U0can be, in examples, equivalent to a consideration of the deviation of the control voltage indicator32from the reference voltage indicator60. The considerations of the controlled voltage indicator Ui.4band the output voltage indicator U0described with respect to Fig can therefore be used accordingly for limiting the control voltage indicator to the control range around the reference voltage indicator60.

FIG.4Bshows a schematic illustration of an example of a limitation of a deviation between output voltage indicator U0(describing, e.g., the reference voltage indicator60or corresponding to the same) and controlled voltage indicator Ui(that can be indicated by the control voltage indicator32) as it can be performed by examples of the regulation apparatus10according toFIG.1, the regulation apparatus110according toFIGS.2,3or the regulation apparatus210according toFIG.15. InFIG.4B, the voltage indicators are shown in Cartesian coordinates, wherein the first and the second coordinate axes can represent a first and a second direction. The first and second directions can be orthogonal directions of a coordinate system. The coordinate system can be static with respect to the output voltage indicator (or the reference voltage indicator60), for example, the same can be selected such that the reference voltage indicator points parallel to the first direction, wherein this is assumed in examples herein for a simplified illustration. However, the coordinate system can also be selected differently and does not have to be static with respect to the reference voltage indicator. The coordinate system can be, for example, a dq coordinate system as inFIG.4B, wherein, in this non-limiting example, the first direction is a vertical direction and represents the q coordinate, and the second direction is a horizontal direction and represents the d coordinate. Accordingly, in the following, the first direction will be referred to as vertical direction and the second direction will be referred to as horizontal direction.

InFIG.4B, a circular area402as well as rectangular areas404,406,408around the output voltage indicator are shown, which can represent examples for determining the amplitude control range44and the angle control range54around the reference voltage indicator60. If the controlled voltage indicator Uiis within the circle402around the output voltage indicator U0, the output current of the current converter80is below a limiting current strength Imax.

Embodiments of the invention include a direct control quantity limitation of the controlled voltage indicator Ui(in phase angle and amplitude) to limit the current to a maximum value. For preventing overcurrent operation, the controlled voltage indicator is maintained in a defined environment to the voltage indicator U0at the terminal point82. The allowable environment can be derived, for example, from the equivalent internal impedance Zi(filter impedance) of the current converter80. At a maximum allowable current, Zican determine the maximum allowable voltage difference (the voltage deviation limiting value) between the controlled voltage indicator Uiand the reference voltage indicator U0(cf.FIGS.4A,4B).

The voltage deviation limiting value, e.g., ΔUmaxcan here, for example be an amount of a vector difference between the output voltage indicator U0and the control voltage indicator32or the controlled voltage indicator Uiin horizontal direction (d direction).

Limiting the control voltage indicator32by means of the limiting module30acts in that way that in cases where the controlled voltage indicator Uireaches the limit of the allowed range as illustrated inFIG.4b,the control voltage indicator32is limited such that the controlled voltage indicator Uiis maintained within the ranges shown inFIG.4B. The control voltage indicator can still move freely within the allowed range, i.e., within the amplitude control range44and the angle control range54, and can accordingly be moved according to a regulator dynamics, for example a grid-forming regulator dynamics, of the control quantity regulation20. Thus, the control voltage indicator32can still react to new situations in a grid-compatible manner.

According to embodiments, the regulation apparatus limits the control voltage indicator32based on the first deviation limiting value46and the second deviation limiting value56. The first deviation limiting value46can describe a limiting value for a deviation of the control voltage indicator32from the amplitude62of the reference voltage indictor60in the first direction and the second deviation limiting value56can describe a limiting value for a deviation of the control voltage indicator32from the reference voltage indicator60in the second direction.

As can be seen fromFIG.4B, a given angle deviation (e.g., a deviation in the angle coordinate) at a large amplitude of the reference voltage indicator60can result in a greater deviation of the controlled voltage indicator Uifrom the reference voltage indicator U0compared to at a small amplitude of the reference voltage indicator60. In order to not exceed the limiting current strength at a large amplitude of the reference voltage indicator60, and to still not unnecessarily limit the angle control range54at a small amplitude of the reference voltage indicator60, it can therefore be advantageous to determine the angle control range54in dependence on the amplitude of the control voltage indicator32. As an alternative to the amplitude of the control voltage indicator32, the amplitude of the reference voltage indicator60can also be considered.

Therefore, according to embodiments, the angle control range determination module53is configured to determine an upper and a lower limit of the angle control54based on a ratio between the second deviation limiting value56and the amplitude of the control voltage indicator32or the reference voltage indicator60.

In examples, the angle control range determination module53can determine the angle control range54by means of a trigonometrical function in dependence on the ratio between the voltage deviation limiting value and the amplitude of the control voltage indicator32or the reference voltage indicator60. By using the trigonometrical function and considering the amplitude of the control voltage indicator, it can be obtained that even when using the polar coordinates amplitude and angle for the limitation of the control voltage indicator, the control voltage indicator can be limited to a rectangular control range. For example, by means of the arcsine, the angle control range can be determined from the ratio between the second deviation limiting value56and the amplitude42of the control voltage indicator32.

For example, the first and second deviation limiting value can be determined by considering the internal impedance86of the current converter80. For example, by means of the selection or determination of the first and the second deviation limiting value, prioritization of the amplitude or vertical component of the angle or horizontal component of the control voltage indicator can be obtained. As can be seem fromFIG.4B, the deviation between the output voltage indicator U0and the controlled voltage indicator Uican be combined of an angle deviation and an amplitude deviation or a vertical and a horizontal voltage deviation.

A similar consideration can also be made for the amplitude control range44, whose upper and lower limit in relation to the amplitude value of the reference voltage indicator60can depend on the actual angle, for example on an actual angle deviation (cf. angle deviation48inFIG.5) between the control voltage indicator and the reference voltage indicator. Accordingly, in embodiments, the amplitude deviation determination module43can determine the amplitude control range44based on the first deviation limiting value46and additionally based on the angle52of the control voltage indicator32.

According to embodiments, the regulation apparatus110is configured to determine the first deviation limiting value46and the second deviation limiting value56in dependence on each other to limit a deviation of the control voltage indicator32from the reference voltage indicator60. The regulation apparatus110can be configured to determine the first and second deviation limiting value in dependence on each other to limit a deviation of the control voltage indicator32from the reference voltage indicator60to a maximum voltage deviation, which is described, for example, by the voltage deviation limiting value.

In examples, the first and second deviation limiting value can be identical. One example for this is shown with the square area406or the outer square area404inFIG.4B. In other examples, such as the rectangular area408inFIG.4B, the first and second deviation limiting value can be selected to be different in order to prioritize one of the components, such as the horizontal or angle component in the case of the area408.

For example, the amplitude control range44and the angle control range54can form a rectangular area around the reference voltage indicator60, for example an inner or an outer rectangle as shown exemplarily inFIG.4B.

In other words, according to embodiments, allowable rectangles are derived from the circle area (cf.FIG.4B). This has the background that the allowable corridors for the vertical voltage range and the horizontal voltage range can each be set independent of the current deviation of the respective different component, whereby the effort for determining the first deviation limiting value46and the second deviation limiting value can be kept low.

Examples of rectangular areas are squares or rectangles (transversal, longitudinal) applied to the inside or outside, whereby the active and reactive component can be prioritized in a different manner for different situations (also in a dynamical manner). From these rectangles, it can be derived directly in what corridor the vertical voltage component and the horizontal voltage component are to be routed.

In examples, the first or second deviation limiting value can be set to predetermined values.

For example, the first deviation limiting value determination45can be configured to determine the first deviation limiting value46in dependence on an angle deviation of the control voltage indicator32from the reference voltage indicator60. In these examples, the second deviation limiting value determination module55can set, for example, the second deviation limiting value56to a predetermined value. The value of the second deviation limiting value56can, for example, be set to a value smaller than or equal to the voltage deviation limiting value. In these embodiments, the first deviation limiting value46is determined in dependence on the angle deviation, i.e., the actual angle deviation. This means in these examples, the second deviation limiting value56can be set to a value that is a large as possible by considering the voltage deviation limiting value, which corresponds to a prioritization of the angle, and the first deviation limiting value46can be selected in dependence on the current angle deviation. In situations where the angle deviation is small, the angle amplitude controller range44can be large, while in situations where the actual angle deviation is large, the amplitude control range44is selected to be small, such that the limiting current strength is not exceeded.

Alternatively, the second deviation limiting value determination module55can be configured to determine the second deviation limiting value46in dependence on an amplitude deviation of the control voltage indicator32from the reference voltage indicator60. In these examples, the amplitude deviation limitation determination module45can be configured to set the first deviation limiting value46to a value, i.e., a predetermined value. The predetermined value can be selected, for example, such that at identical angles of the control voltage indicator and the reference voltage indicator and at an amplitude deviation corresponding to the first deviation limiting value46, the limiting current strength is not exceeded. In this alternative, prioritization of the amplitude (or the first direction) takes place, while the angle control range54is determined in dependence on the actual amplitude deviation (or deviation in the first direction).

In the above examples, where the first deviation limiting value46or the second limiting deviation limiting value56are determined in dependence on the angle deviation or the amplitude deviation, the first deviation limiting value or the second deviation limiting value can be determined such that the limiting current strength is not exceeded when utilizing the specific limiting value.

By determining the first deviation limiting value46in dependence on the angle deviation or determining the second deviation limiting value56in dependence on the amplitude of the amplitude deviation, with respect toFIG.4B, the full circle determined by the voltage limiting value can be utilized without exceeding the voltage deviation limiting value when fully utilizing the first deviation limiting value46and the second deviation limiting value56.

In other words, the circular allowed environmental range having the radius r, which determines the maximum voltage difference (resulting from the set maximum current and an internal impedance of the current converter plant), in one variation, specifications for the voltage angle and amplitude can be divided as follows. First, it has to be stated that the vertical component (d axis) and the horizontal component (q axis) depend on each other by the mathematical circle description (r2=d2+q2) when the circle area is to be utilized fully but not exceeded. This means the more the vertical component is limited the more free space/reserve is available for the allowed difference in horizontal direction and vice versa. Therefore, prioritization can be determined in advance. As, for example, the fed-in active power is frequently prioritized and the same is determined in an inductive internal impedance by the angle difference (vertical component or d component), the deviation in vertical direction (d axis) can be the complete radius r, in examples, i.e., the second deviation limiting value56can be set to the radius of the circle. In a further step, the allowed deviation of the horizontal components depends on the actual deviation of the actual vertical component. Here, the d or q components describe the allowed deviation in horizontal or vertical direction in Cartesian coordinates:

The limitation and control ranges can subsequently be transferred to polar coordinates (angle, amplitude).

Depending on how the prioritization is selected and the internal impedance is combined of ohmic-inductive components, an adaptation can be performed by scaling one component and the one component is derived from the other actual component according to the circle description.

Generally, it has to be stated that the limiting method of the regulation apparatus110as described with respect toFIGS.1to4can be suitable for all current converter plants where a voltage, e.g., Ui, is controlled behind an internal impedance. This applies in particular for so-called grid-forming or voltage-impressed regulated current converters. The variation of a grid-forming regulation20as described with respect toFIG.7can serve as implementation example, but the limitation method is not limited to that.

The control quantity limitation can be based, for example, among others on the internal impedance of the current converter Zi. The output filter (sinusoidal filter) of the current converter80forms normally the dominant portion of the internal impedance86of the current converter80. The nominal values of the output filter impedance can typically be inferred from the respective data sheets or can be determined with measurement technology, wherein additional apparatuses can be used to determine temporal changes of the impedance. For determining the internal impedance as accurately as possible, the impedances of further components such as the power semiconductors can be used.

According to embodiments, in order to counteract the frequency dependency of the inductive portion jωL of the current converter internal impedance86, a respective scaling Im{Zi}·fn/f0can be implemented. Here, the grid frequency is taken, for example, from a PLL (Phase-Lock-Loop) or results from the controlled voltage indicator32.

This extension allows the usage of the method also in grids having a high frequency deviation from a nominal grid frequency. In conventional grid structures, this influence can be neglected due to the typically narrow frequency bands.

In the following, with respect toFIG.5, an example for a basic structure for calculating the control quantity limitations will be presented. Based thereon, the same is transferred into the context of the current converter regulation in different variations.

FIG.5illustrates an example of a control range determination31as it can be implemented in examples of the regulation apparatus110ofFIG.2. The control range determination can represent the modules43,45,53,55ofFIG.2andFIG.3. According to the example ofFIG.5, the amplitude control range44is provided in the form of an upper limiting value Umaxand a lower limiting value Uminfor the amplitude42of the voltage indicator32. Analogously, the angle control range54is provided in the form of an upper limiting value ϑmaxand a lower limiting value ϑminfor the angle52of the control voltage indicator32. According to the example ofFIG.5, the regulation apparatus comprises a module66that is configured to determine the amplitude62and the angle64of the reference voltage indicator60based on the reference voltage indicator60. According to the example shown inFIG.5, the control range determination31is configured to determine the first deviation limiting value46based on the internal impedance86and to determine the lower and the upper limit of the amplitude control range44based on the first deviation limiting value46and an angle deviation48between the reference voltage indicator60and the control voltage indicator Us. Further, the control range determination31according toFIG.5is configured to determine the second deviation limiting value56based on the internal impedance86and to determine the lower and the upper limit of the angle control range by using a trigonometrical function58based on the second deviation limiting value56as well as the amplitude42of the control voltage indicator32.

For example, the voltage indicators as well as the internal impedance can be considered in a per unit system. The limiting module31according toFIG.5could then, for example, determine the control value limitations (Umax, Umin, ϑmin, ϑmax) based on the following equations:

The limits for the maximum and minimum voltage amplitude control value Umaxand Uminare formed, for example, from the deviation of the height of the present input indicator |U| and the internal impedance |Zi| of the current converter. This describes the allowable vertical voltage deviation. The same is subsequently transferred into an allowable amplitude deviation based on a correction term kabs, for example by adding the current angle deviation ϑΔOSbetween control and reference voltage indicator.

The angle control quantity limitations are defined, for example, by the limits εmaxand ϑmin. The same are formed as deviation to the current angle of the input signal ∠Uby the trigonometrical function arc sin(|Zi|·khor/|Us|) in dependence on the internal impedance |Zi| and the current control amplitude |Us|. The current control amplitude can, for example, indicate the amplitude42of a previous clock or the current clock. Thereby, the angle control quantity limitations can be defined in dependence on the height of the control indicator. This is necessary for high deviations to the nominal voltage (for example in the FRT case).

For the example of a prioritization of the angle, the allowable deviation in horizontal direction i.e., towards the left and right from the output side voltage indicator, can be the starting point. Therefrom, the maximum angles are determined as allowable environment for the output voltage via the trigonometrical function. Based on the arc sine from the allowable deviation in horizontal direction and the amplitude of the internal voltage indicator, the angle deviation can be determined.

With the help of the amplitude limitation parameter kver(e.g., the first deviation limiting value46) for which, for example, kver∈[0, 1] can apply, and the angle limitation parameter khor(e.g., the second deviation limiting value56) for which, for example kor∈[0, 1] can apply, the allowable corridors (in the case of a square or rectangular control quantity limitation) can be determined. The same act analogously to a proportional scaling of the internal impedance.

In the variation of a circular specification of the allowable range, the amplitude limiting parameter kverfor which also, for example, kver∈[0, 1] can apply, and the angle limitation parameter khor, for which also, for example, kver∈[0, 1] can apply, can also be used to determine the allowable corridors, by prioritizing and scaling the same accordingly in a dynamic manner, as described above with the determination of the first deviation limiting value46in dependence on the angle deviation or the determination of the second deviation limiting value48in dependence on the amplitude deviation. For example, the determination can be made by

with ϑΔOSand Us, the current deviations to the used output voltage (e.g., the reference voltage indicator60). Depending on the priority, these are conditional corridors. Instead via equation 6, the conditional corridors can also be determined via the present current. In examples, the determination can be made such that all in all always the following applies:

In examples, the reference voltage indicator60for the determination66of the amplitude62and the angle64can be determined of a combination of a measurement quantity84describing the output voltage and one or several correction contributions71,72which can each be represented by a voltage indicator. The correction terms71,72can be combined, for example, with the voltage indicator describing the output voltage, i.e., added to or subtracted from the same in order to obtain the reference voltage indicator60. Examples for the correction terms71,72are described with reference toFIG.9.

In other words, a variation for implementing the control quantity limitation30is based on a sum of the three complex voltage indicators: The output voltage indicatorU0, the voltage indicatorUNMas well as the voltage indicator ΔU. After the summation, decomposition into the amplitude portion |U| and the phase angle ∠Utakes place.

According to embodiments, the regulation apparatus110is configured to limit the angle42of the control voltage indicator32further with respect to a change compared to the angle of the reference voltage indicator60of an earlier clock. For example, the limiting module30can comprise an angle change limiting module that is configured to obtain the angle52of the control voltage indicator32as input quantity and to limit the same with respect to the change compared to the angle of the reference voltage indicator60of an earlier clock. Alternatively, the angle change limiting module can also be arranged in front of the angle limiting module51. Accordingly, the angle change limiting module can obtain and limit the angle52′ of the set control voltage indicator32′ and provide the angle limited with respect to the change of the angle to the angle limiting module52as an input quantity. As a further alternative, the angle change limiting module can act on the reference voltage indicator60, i.e., the angle change limiting module can be configured to limit the reference voltage indicator60with respect to a change compared to the angle of the reference voltage indicator of an earlier clock. In this case, the angle64of the reference voltage indicator60limited with respect to its change can be provided to the angle control range determination module53and optionally to the first deviation limiting value determination module45.

FIG.6illustrates an example of an angle change limiting module74. The example of the angle change limiting module74shown inFIG.6is configured to limit the angle64of the reference voltage indicator60used for the limitation of the control voltage indicator32with respect to an angle change compared to the angle of the reference voltage indicator of an earlier clock. The angle change limiting module74comprises a limiter39that is configured to limit the angle64to a range between a lower angle limiting value37and an upper angle limiting value38in order to obtain a limited angle64′. The angle change limiting module74is configured to determine the lower angle limiting value37based on the angle64′ of a previous clock as well as a first angle change limiting value76, wherein the first angle change limiting value76is based on a lower limiting value for a frequency of the reference voltage indicator60. Further, the angle change limiting module74is configured to determine the upper angle limiting value38by combining the angle64′ of a previous clock as well as a second angle change limiting value75, wherein the second angle change limiting value75is based on an upper limit for the frequency of the reference voltage indicator60.

In other words, to prevent uncoordinated drifting of the frequency, as an extension of the method, the lower and upper limit of the angle change (speed) can be implemented by which the set voltage indicator is guided at least or at most. The same can be applied, for example, to the angle change of the measured output voltage or the reference voltage indicator. In the case of a grid frequency of 50 Hz of the grid8, the tolerance limits can, for example, be the standard 47.5 Hz and 52 Hz. This example of the limitation of the angle change speeds can be obtained by the implementation of a minimum or maximum angle speed shown inFIG.6. For a clock cycle of Ts, the change of the angle with respect to its preceding value is limited to ωmaxTs or ωmin·Ts.

In the example shown inFIG.6, instead of the angle64, the limited angle64′ is provided to the angle control range determination module53and optionally to the first deviation limiting value determination module45.

FIG.7illustrates an example of the control quantity regulation20as it can be implemented optionally in the regulation apparatus110, e.g., the regulation apparatus110according toFIG.1. The control quantity regulation20according toFIG.7is an example of a grid-forming regulation. By using the grid-forming regulation according toFIG.7, the current converter80can inherently provide grid-compatible behaviour, such as system inertia. kpand kqrepresent static parameters. k′pand k′qrepresent parameters for the phase pre-control. The control quantity regulation20according toFIG.7receives the quantities P and Q as input quantities. The regulation apparatus110can determine the quantities P and Q based on the one or several measurement quantities84determined at the terminal point82. The quantities U*, f0, P0, Q0represent nominal values, i.e., set values for the voltage, the frequency, the active power and the reactive power of the grid8. The control quantity regulation20can be configured to provide the set control voltage indicator32′ to regulate the current converter80to the nominal values for the grid8.

FIG.8illustrates a further example of the regulation apparatus110in which the limiting module30can be implemented, for example according to the limiting module30ofFIG.5. The regulation apparatus110according toFIG.8comprises a control quantity regulation20, which represents a modified form of the control quantity regulation20according toFIG.7. The control quantity regulation20according toFIG.8can have a similar or equivalent system behaviour as the control quantity regulation20ofFIG.7, wherein TA·kp=Tmapplies for the constant. In the control quantity regulation20according toFIG.8, the PT1 components of the control quantity regulation20ofFIG.7are implemented by integrators with a negative feedback loop. Additionally, the variation of the regulation method ofFIG.8can be equipped with saturation blocks in combination with the tracking anti-windup method of [6]. Additionally, the factors kAWϑand kAWUmap the proportionality factors of [6].

According to embodiments, the regulation apparatus110is configured to use the control voltage indicator32, for example of an earlier clock, for determining the set control voltage indicator32′. One example of such an implementation is shown inFIG.8, wherein the amplitude42of the control voltage indicator32is used for determining the amplitude42′ of the set control voltage indicator32′, and the angle52of the control voltage indicator32is used for determining the angle52′ of the set control voltage indicator32′.

The feedback of the control voltage indicator32for determining the set control voltage indicator32′ can prevent that the set control voltage indicator32′ diverges due to a difference between the set control voltage indicator32′ and the control voltage indicator32that can exist in the case of limiting the set control voltage indicator32′ in the limiting module30.

According to embodiments, the regulation apparatus110is configured to determine the amplitude42′ and the angle52′ of the set control voltage indicator32′ by using respective integrators35,36. According to these embodiments, the regulation apparatus is configured to lead an integrator input quantity33of the integrator35used for determining the amplitude42′ of the set control voltage indicator32′ to zero in the case of a deviation of the amplitude42of the control voltage indicator32from the amplitude42′ of the set control voltage indicator32′, or to reinitialize the integrator35used for determining the amplitude42′ of the set control voltage indicator32′, for example with a suitable initial value. Further, according to these embodiments, the regulation apparatus110is configured to lead an integrator input quantity34of the integrator36used for determining the angle52′ of the set control voltage indicator32to zero in the case of a deviation of the angle52of the control voltage indicator32from the angle52′ of the set control voltage indicator32. Alternatively, the regulation apparatus can reinitialize the integrator36used for determining the angle52′ of the set control voltage indicator32in the case of the deviation, for example with a suitable initial value.

According to embodiments, the control quantity regulation20is configured to determine the amplitude42′ of the set control voltage indicator based on a difference of a measurement quantity Q describing a reactive power of an output power of the current converter80and a set value Q0for the reactive power. Further, according to this embodiment, the control quantity regulation20is configured to determine the angle52′ of the set control voltage indicator32′ based on a measurement quantity P describing an active power of the output power of the current converter and a set value P0for the active power, and further based on a difference between the amplitude42′ of the set control voltage indicator and a set value U* for an amplitude of the output power of the current converter80. One example of these embodiments is shown inFIG.8. By considering the amplitude42′ of the set control voltage indicator and the set value U* when determining the angle52′, the dynamics of the control quantity regulation20can be improved. It should be noted that considering the amplitude42′ of the set control voltage indicator and the set value U when determining the angle52′ can be implemented independent of the type of feedback or the anti-windup as illustrated inFIG.8.

According to embodiments, the current converter80, for which the regulation apparatus110described with reference toFIGS.1to8determines the control voltage32, is a multi-phase current converter. The multi-phase current converter is configured to provide a respective voltage for each of a plurality of phases. In embodiments, the current converter80is configured to provide the respective voltages for the plurality of phases based on the control voltage32. In alternative embodiments, the regulation apparatus110is configured to provide a respective control voltage32for each of the phases, and the current converter80is configured to adjust the voltage for the respective phase based on the control voltage32allocated to the respective phase. In the following, an example of a multi-phase current converter as well as different embodiments of the regulation apparatus110for a multi-phase current converter will be described.

FIG.9illustrates an embodiment of the current converter80as multi-phase current converter. According to an embodiment ofFIG.9, the current converter80, a three-phase current converter, is configured to provide one voltage each for a first phase U, a second phase V and a third phase W of a three-phase grid. Via a first internal impedance861, a first switching node881is coupled to a first terminal point where the current converter80is connected to the first phase of the grid. Via a second internal impedance862, a second circuit node882is connected to a second terminal point822where the current converter80is coupled to the second phase of the grid. Via a third internal impedance863, a third circuit node883is coupled to a third terminal point823where the current converter80is connected to the third phase W of the grid. This means that, for each of the plurality of phases, the current converter80comprises a circuit node88allocated to the respective phase. Via a respective internal impedance86, the circuit nodes88are coupled to a terminal point82allocated to the phase allocated to the respective terminal point88.

According to the example ofFIG.9, the current converter80comprises a half bridge for each of the phases (half bridges831,832,833for the first, second and third phase U, V, W), which are controlled by means of respective modulation (e.g., pulse width modulation (PWM) based on the control voltage Us1, Us2, Us3allocated to the respective phase to provide the respective indicated voltage Ui1, Ui2, Ui3(also referred to as respective bridge voltage, cf. bridge voltage87inFIG.18). For example, the half bridges83provide the bridge voltage based on an intermediate circuit voltage89applied to the half bridges, which can be applied between intermediate circuit voltage supplies. The intermediate circuit voltage can be a direct voltage. Optionally, the current converter can comprise an intermediate circuit not shown inFIG.9, which is arranged between intermediate circuit voltage supplies.

The current converter80can be configured to obtain or determine the control voltages Us1, Us2, Us3for the respective phases U, V, W, based on a control voltage32provided by the regulation apparatus110, or can alternatively be configured to obtain or determine the respective control voltages Us1, Us2, Us3based on several control voltages provided by the regulation apparatus110.

The implementation of the current converter80shown inFIG.9can represent a three-phase jumper and can represent an example for an implementation of the equivalent diagram of the current converter80shown inFIG.4A. For example, inFIG.4A, the illustrated voltage Uiand the output voltage U0can each represent a geometrical space indicator which is represented by the respective set voltages Ui1, Ui2, Ui3or the respective output voltages U01, U02, U03for the phases U, V, W.

As illustrated inFIG.9, the reference point for the measurement of the set voltages (i.e., the indicated voltages)88can be different from a reference point for the measurement of the output voltages for the phases U, V, W. This potential difference can be considered in examples when determining66the amplitude62and the angle64for the limitation of the control voltage, such as shown inFIG.5but also inFIGS.12and13, where the potential difference UNMbetween the reference point M for the indicated voltages and the reference point N for the output voltages can be considered in the form of a correction term72, which can exist, for example, in the form of a voltage indicator.

In other words, the circuit diagram ofFIG.9can represent an example for the current converter ofFIG.4A, wherein the controlled voltage Uiand the output voltage U0are considered instead of an illustration by means of geometrical space indicators, the controlled bridge voltage Uiand the used output voltage U0separately for each phase. Depending on the hardware topology, when implementing the method, the reference point of the measurement of the used output voltage and the reference point of the controlled voltage at the half bridges (HB 1,2,3) is to be considered. If these two reference points have a potential difference, the allowable environmental range around this voltage (UNM) is to be corrected. For example, the potential difference can be caused by a different neutral point shift.

The control voltageUs, of which the PWM control is formed, and the result, the controlled voltageUiat the output of the bridges (bridge output voltage) are to be distinguished. Depending on the type of modulation and voltage proportions of 50 Hz and 100 Hz in the intermediate circuit, for example, an additional contribution to the fundamental oscillation of Uican result. This deviation is referred to as ΔUand can be added when determining the limiting values, for example in the form of the correction term71inFIG.5. In this context, the relevant frequency portions can be extracted from the voltage values of the divided intermediate circuit (for example by a Fourier analysis, transformation).

On the other hand, the above stated deviation between control voltage Usand the bridge voltage Uican also be considered when implementing the modulation, for example by adapting the pulse width depending on the additional oscillation in the intermediate circuit.

In embodiments, the limitation of the control voltage indicator32, for example according to the control quantity limitation based onFIG.5, can be implemented both for the fundamental oscillation as well as for the harmonic in a parallel structure. This can, for example, mean to perform the control quantity determination31separately for the fundamental oscillation and for the harmonic.

It should further be noted that implementing the current converter80by means of the intermediate circuit81is possible on a single-phase current converter or in an equivalent manner a current converter having any number of phases.

According to embodiments, the current converter80comprises an intermediate circuit811. The intermediate circuit811is configured to provide a bridge voltage Ui1indicated by the control voltage, based on the control voltage Us1, for example the control voltage32, and an intermediate circuit voltage89at the circuit node881coupled to the terminal point821of the current converter80via the internal impedance861of the current converter80.

Here, the regulation apparatus80can be configured to consider, when determining the reference voltage indicator60, a potential difference UNMbetween a reference voltage M of the bridge voltages Uiand a reference voltage N of the output voltages U0, for example as described with respect toFIGS.18to20.

Alternatively or additionally, the regulation apparatus110can be configured to consider, when determining the reference voltage indicator60, a contribution of harmonics of a voltage fundamental oscillation in the intermediate circuit to the bridge voltage, for example as described with respect toFIGS.18to20.

FIG.10illustrates a control range determination as it can be implemented in examples of the regulation apparatus110for regulating a multi-phase current converter80, in particular the regulation apparatus110according toFIG.11. According to the embodiment inFIG.10, the regulation apparatus110determines an amplitude control range44and an angle control range54for each of a plurality of phases of the current converter80, for example for each of three phases U, V, W of a three-phase current converter, for example the three-phase current converter80ofFIG.9. According to the embodiment ofFIG.10, the regulation apparatus110determines, based on one or several measurement quantities84describing the output voltages of the plurality of phases of the current converter80, for example a space voltage indicator U0,abc, a respective reference voltage indicator for each of the phases of the current converter. For the example of the three-phase current converter, the regulation apparatus110can determine, as shown inFIG.10, a first reference voltage indicator601for the first phase, a second reference voltage indicator602for the second phase and a third reference voltage indicator603for the third phase. Optionally, the regulation apparatus110can consider one or several of the correction factors71,71, for determining the reference voltage indicator601,602,603, as described with reference toFIGS.5and9. Here, in examples, the correction factors can be determined separately for each of the phases and can be considered in the respective control quantity determination31for the phases. The reference voltage indicators for the respective phases can each be subject to a coordinate transformation1101, for example a Clarke transformation to obtain the respective reference voltage indicator in αβ coordinates. Alternatively, the reference voltage indicators can also be subject to a Park transformation to obtain the reference voltage indicator in dq coordinates. According to the example ofFIG.10, the reference voltage indicators601,602,603are each supplied to a control quantity determination module31as described with respect toFIG.5to determine the respective amplitude control range44and the respective angle control range54for the respective phase of the current converter.

In other words, according to the example ofFIG.10, the control quantity determination is performed, in a phase separate manner, i.e., separately in the individual phases or individually for the individual phases. For the example of the three-phase current converter, this means that a first control quantity determination module311determines, based on the reference voltage indicator601for the first phase, the amplitude control range441and the amplitude control range541for a control quantity for the first phase. Accordingly, a second control quantity determination module312determines, based on the reference voltage indicator602, the amplitude control range442and the angle control range542for the second phase and a third control quantity determination module313, based on the reference voltage indicator603, the amplitude control range443and the angle control range543for the third phase. The first control quantity determination module311can use an amplitude421of the control voltage indicator for the first phase for determining the angle control range541or alternatively, the amplitude of the reference voltage indicator601. This means the control range determination modules31for the respective phases can use, for determining the respective angle control range54for the respective phase, the amplitude421,422,423of the control voltage indicator for the respective phase or the amplitude of the respective reference voltage indicator601,602,603of the respective phase.

In other words, according to embodiments of the regulation apparatus110, starting from the three-phase output voltage U0,abcof the current converter that has been determined by means of measurement technology, to which optionally the voltageUNMand/or the voltage ΔUcan be added, first, the individual phases are separated. Subsequently, the same are decomposed into αβ coordinates. In alternative embodiments, decomposition into dq coordinates takes place. One method for decomposition into αβ coordinates is offered by the usage of SOGI (Second Order Generalized Integrator) [5]. In the method for decomposition of individual signals, it is decisive that the time constant for the quadrature process is below the time constant of the internal impedance. When the signals are provided in a Clarke-transformed illustration, calculation of the respective phase angles ∠Ũo,a, ∠Ũo,b, ∠Ũo,cand their amplitudes |Ũo,k| (with k=a, b, c) is performed. Additionally, the control amplitudes |Us,k| (with k=a, b, c) are inferred dynamically for calculating the control quantity limitation from the three-phase amplitudes of the control signals according toFIG.11. Subsequently, the control quantity limitations Umin,k, Umax,k, ϑmin,k, ϑmax,k, with k=a, b, c will be calculated, as described with reference toFIG.5.

FIG.11illustrates an embodiment of the regulation apparatus110according to which the regulation apparatus110provides one control voltage indicator each for a plurality of phases. In the example shown inFIG.11for a three-phase current converter, the regulation apparatus110is configured to provide a first control voltage indicator with amplitude421and angle521for the first phase, a second control voltage indicator with amplitude422and angle522for the second phase, and a third control voltage indicator with amplitude423and angle523for the third phase. The amplitudes421,422,423and the angles521,522,523of the control voltage indicators for the plurality of phases are each limited separately, wherein the respective amplitude control ranges441,442,443and the angle control ranges541,542,543can be determined separately for the individual phases, for example, as described with reference toFIG.10.

According to the embodiment inFIG.11, the set control voltage indicator32′ describes the set control voltage for the plurality of phases and the regulation apparatus110is configured to determine, for each of the phases based on an amplitude42′ of the set control voltage indicator32′ a respective amplitude42′1,42′2,42′3and to determine an angle52′1,52′2,52′3for each of the phases based on an angle52′ of the set control voltage indicator32′. According to these embodiments, the regulation apparatus110limits the amplitudes and angles of the respective phases separately.

The determination of the set control voltage indicator32′ can take place by the regulation apparatus110according toFIG.11as described with respect to the regulation apparatus110according toFIG.8.

In other words,FIG.11illustrates a modified version of the grid-forming regulation method ofFIG.7. In examples, both regulation methods can comprise an equivalent system behavior, wherein TA·kp=Tmapplies for the constant. Further, the PT1 components ofFIG.7are implemented by integrators with a negative feedback loop. Additionally, the modified variation of the regulation method ofFIG.7is provided with saturation blocks in combination with the tracking anti-windup method of [6]. The factors kAWϑand kAWUmap the proportionality factors of [6]. The blocks “Satlogic” are provided with a logic forming the sum ΣSatϑsor ΣSat|Us|of the respective three input signals ΣSatϑkrespective ΣSat|Uk|with k=a, b, c as soon as these each have a valence unequal zero. Subsequently, the inputs of the respective integrators of the respective sums ΣSat|Ui|, ΣSatϑiare provided. The limits of the saturation blocks are dynamically determined according toFIG.10.

For phase-separate control quantity limitation, the control signals are transformed into a three-phase indicator illustration and subsequently used for controlling the power semiconductors with the help of different modulation methods. This can be obtained from the view of the respective control values of the phase ϑsby additional paths with phase shifts by −⅔π or − 4/3π. The control values of the amplitudes |Us| are also transformed into a three-phase indicator illustration and subsequently represent the amount of the single-phase voltage indicators |Us,a|, |Us,b|, |Us,c|. By separating the phases, an immediate control quantity limitation can be obtained based on the respective control quantities ofFIG.6. By the control quantity limitation of the control voltage amplitudes |Us,a|, |Us,b|, |Us,c| and the control angles ϑs,a, ϑs,b, ϑs,c, the control signals always fulfil equations Eq. 8 and Eq. 9:

The implementation with phase-separate control quantity limitation described with reference toFIGS.11and12and determination of a respective control voltage indicator for each of the plurality of phases can be particularly advantageous for grids where imbalance between the phases of the grids can occur.

For example, with reference to the current converter80ofFIG.9, the first control voltage Us1can be described by the amplitude421and the angle521, the second control voltage Us2can be described by the amplitude422and the angle522, and the third control voltage Us3can be described by the amplitude423and the angle522.

FIG.12illustrates an example of a control quantity determination for balanced three-phase grids. In the case of balanced three-phase grids, the control voltages, for example, the control voltages Us1, Us2, Us3ofFIG.9can be described by means of a common control voltage indicator. Analogously, the output voltages of the three phases, for example, U01, U02, U03ofFIG.9can be described by means of a common reference voltage indicator60. Accordingly, according to embodiments, in particular, embodiments for balanced grids, the regulation apparatus110can obtain, the reference voltage indicator60based on the one or several measurement quantities84describing the output voltages of the three phases, for example, the three phases U, V, W of the current converter80. Here, the regulation apparatus110can optionally consider the correction terms71and72as described with reference toFIGS.5and9. According to the embodiment ofFIG.12, the regulation apparatus110can transform the control voltage indicator60describing the three phases of the current converter80by means of a transformation1101and supply the transformed control voltage indicator to the control range determination module31. As described with reference toFIG.10, the transformation1101can be a Park transformation or a Clarke transformation. The control range determination31can be implemented as described with reference toFIG.5. This means, according to these embodiments, the regulation apparatus110can be configured to limit a common control voltage indicator for the three phases of the three-phase current converter80.

Embodiments of the regulation apparatus110for balanced grids can be configured as shown inFIG.8, wherein the control voltage indicator32, or in this case, the set control voltage indicator32′ represents a control voltage indicator for the three phases of a three-phase current converter. Based on the set control voltage indicator32determined by the regulation apparatus110, the current converter80can determine a respective control voltage for each of the three phases of the current converter. For example, the current converter80according toFIG.9can be configured to determine the first control voltage Us1, the second control voltage Us2and the third control voltage Us3based on the control voltage32.

In other words,FIG.8in combination withFIG.12can represent an embodiment for determining the dynamic control quantity limitation for three-phase balanced grids that can be implemented, for example, as described with reference toFIG.5.

For balanced grids, the control quantity limitations can be realized based on the sum of: the three-phase output voltage U0,abcof the current converter determined by measurement technology, the voltageUMNas well as the voltage ΔUand a subsequent Clarke transformation (Ũo,αβ0). The amplitude of the controlled voltage indicator |Us| is inferred dynamically according toFIG.8. Subsequently, the calculation of the control quantity limitation (Umax, Umin, ϑmax, ϑmin) takes place as described with reference toFIG.5. The grid-forming regulation method ofFIG.8can be implemented like the regulation method ofFIG.11and can comprise an equivalent or similar system behavior as the regulation method ofFIG.11, wherein here also TA·kp=Tmapplies for the constant. Deviating therefrom, the regulation method includes the control quantity specification ofFIG.12, i.e. limitation is performed together for all phases and the feedback loop for the anti-windup can be adapted accordingly. For example, saturation blocks are integrated and two integrators are provided with the tracking anti-windup method [6]. The factors kAWϑand kAWUadditionally form the proportionality factors of [6].

By the control quantity limitation of the control voltage amplitude |Us| and the control angle ϑs, the two control signals always fulfil the same equations Eq. 10 and Eq. 11:

According to embodiments, the current converter80is a multi-phase current converter and the reference voltage indicator60describes a plurality of output voltages U01, U02, U03, each allocated to a phase of a plurality of phases U, V, W of the current converter80. According to the embodiments, the current converter80is configured to provide a voltage Ui1, Ui2, Ui3indicated by the control voltage32for each of the phases. For example, the current converter80provides the voltage indicated by the control voltage32for the phases at the terminal point881,882,883allocated to the respective phase, which is connected to the terminal point of the respective phase by means of the internal impedance861,862,863.

FIG.13illustrates a further embodiment of the regulation apparatus110that is configured for a three-phase current converter, for example, for the current converter80according toFIG.9. According to the example ofFIG.13, the current converter is configured to provide, in dependence on the control voltage32, one voltage each for the first phase U, the second phase V and the third phase W of the three-phase current converter80. According to the embodiment ofFIG.13, the regulation apparatus110is configured to regulate the control voltage32in positive-phase sequence system, negative-phase sequence system and zero-phase sequence system components. The regulation apparatus110according toFIG.13comprises a positive-phase sequence system regulation110pthat is configured to determine a positive-phase sequence system control voltage indicator32p. Further, the regulation apparatus110according toFIG.13comprises negative-phase sequence system regulation110nthat is configured to determine a negative-phase sequence system control voltage indicator32n. Optionally, the regulation apparatus110can comprise a zero-phase sequence system regulation1100that is configured to determine a zero-phase sequence system control voltage indicator320. The positive-phase sequence system control voltage indicator32p, the negative-phase sequence system control voltage indicator32nand the zero-phase sequence system control voltage indicator320describe together the control voltage32based on which the current converter80can determine a control voltage each for each of the three phases of the current converter80, for example, the first control voltage Us1, the second control voltage Us2and the third control voltage Us3(cf.FIG.9). The positive-phase sequence system regulation110pis configured to determine a positive-phase sequence system set control voltage indicator based on one or several measurement quantities84describing the output voltages of the three phases of the current converter (cf.FIG.1) and to limit an amplitude42′pand an angle52′pof the positive-phase sequence system control voltage indicator to determine an amplitude42pand an angle52pof the positive-phase sequence system control voltage indicator32p. For example, the positive-phase sequence system regulation110pcan be configured according to the regulation for balanced systems shown inFIG.8, wherein in the case of the positive-phase sequence system regulation110pthe regulated voltage describes the positive-phase sequence system of the output voltages of the three phases. The positive-phase sequence system110pcan be configured to limit the amplitude42′pto an amplitude control range44pto obtain the amplitude42p. Further, the positive-phase sequence system regulation110pcan be configured to limit the angle52′pto an angle control range54pto obtain the angle52p.

In the example ofFIG.13, the respective output voltages of the first, second and third phase of the current converter80can be described by means of a positive-phase sequence system reference voltage indicator60p, a negative-phase sequence system reference voltage indicator60n and a zero-phase sequence system reference voltage indicator600(cf.FIG.14). The positive-phase sequence system regulation110pcan be configured to regulate the positive-phase sequence system reference voltage indicator60p. In examples, the negative-phase sequence system regulation110ncan be configured to regulate the negative-phase sequence system reference voltage indicator60nto zero and the zero-phase sequence system regulation1100can be configured to regulate the zero-phase sequence system reference voltage indicator600to zero. For this, the negative-phase sequence system regulation110nand the zero-phase sequence system regulation1100can comprise a negative-phase sequence system control110nor a zero-phase sequence system control1100. The negative-phase sequence system control110nprovides an amplitude42′nand an angle52′nof a negative-phase sequence system set control voltage indicator. The negative-phase sequence system regulation110nis configured to limit the amplitude42′nto an angle control range44nto obtain an amplitude42nof the negative-phase sequence system control voltage indicator32n. Further, the negative-phase sequence system regulation110nis configured to limit an angle52′nof the negative-phase sequence system set control voltage indicator to an angle control range54nto determine an angle52nof the negative-phase sequence system control voltage indicator32n. The zero-phase sequence system control1110is configured to determine an amplitude42′0and an angle52′0of a zero-phase sequence system set control voltage indicator. The zero-phase sequence system regulation1100can be configured to limit the amplitude42′0to an amplitude control range420to determine an amplitude420of the zero-phase sequence system control voltage indicator320. Further, the zero-phase sequence system regulation1100can be configured to limit the angle52′0to an angle control range540to determine an angle520of the zero-phase sequence system control voltage indicator320.

In other words, according to embodiments, the control quantity limitation can be configured in positive-phase, negative-phase and zero-phase sequence system. According to standard, the grid-forming regulation is configured for the positive-phase sequence system. The limitation of the positive-phase sequence system can hence take place in examples analogously to the balanced case as described with reference toFIG.12orFIG.8. The negative-phase and zero-phase sequence system are controlled in these examples by the value zero to obtain ideal balancing. Depending on the imbalance of the grid, counter- or zero-currents of any amount can occur. Therefore, in examples, the regulation apparatus110comprises a regulation110nof the negative-phase sequence system and the regulation1100of the zero-phase sequence system of the control voltage that can limit or harmonize the balancing amount. In dependence on the regulation task with respect to the negative-phase or zero-phase sequence system, control limitation can be put down in a similar manner (cf.FIG.14).

FIG.14illustrates an example of a control range determination in the positive-phase, negative-phase and zero-phase sequence system. According to the example ofFIG.14, the regulation apparatus110is configured to determine the amplitude control range44pand the angle control range54pfor the positive-phase sequence system, the amplitude control range44nand the angle control range54nfor the negative-phase sequence system as well as the amplitude control range440and the angle control range540for the zero-phase sequence system. In other words, the regulation apparatus110can determine separate control quantity limits for the positive-phase, negative-phase and zero-phase sequence system. The regulation apparatus110can comprise a positive-phase sequence system control range determination31pthat is configured to determine the amplitude control range44pand the angle control range54pbased on a positive-phase sequence system reference voltage indicator60p. Accordingly, the regulation apparatus110can comprise a negative-phase sequence system control range determination31nthat is configured to determine the amplitude control range44nand the angle control range54nbased on a negative-phase sequence system reference voltage indicator60n. Further, the regulation apparatus110can comprise a zero-phase sequence system control range determination310that is configured to determine the amplitude control range440and the and the angle control range540based on a zero-phase sequence system reference voltage indicator60o. According to the embodiment ofFIG.14, the regulation apparatus110can comprise a positive-phase, negative-phase and zero-phase decomposition141, which can be configured to determine the positive-phase sequence system voltage indicator60p, the negative-phase sequence system reference voltage indicator60nand the zero-phase sequence system reference voltage indicator600based on a reference voltage indicator60. As described with reference toFIGS.5and9, also in these embodiments, the reference voltage indicator60can be determined based on the one or several measurement quantities84as well as optionally one or several of the correction terms71,72.

The control range determination31p,31n,310can be implemented, for example, according to the control range determination31ofFIG.5. Here, the first and second deviation limiting values can be determined separately for the positive-phase sequence system, the negative-phase sequence system and the zero-phase sequence system.

In other words, starting from the reference voltage indicatorU0to which optionally the voltage indicatorUNMas well as the voltage indicator ΔUcan be added, according to the embodiment ofFIG.13, a decomposition (for example according to [7]) into a positive-phase sequence system voltageŨopand a negative-phase sequence system voltageŨonand a zero-phase sequence system voltageŨo0for calculating the phase angles ∠Ũop, ∠Ũon, ∠Ũo0, and amplitudes |Ũop|, Ũon|, Ũo0| can take place. Analogously to embodiments ofFIGS.8and10, the capacitor voltage at the sinusoidal filter or the voltage at the grid coupling of the current converter can also be used. Additionally, the control voltage amplitudes for the positive-phase sequence system |Usp|, the negative-phase sequence system |Usn| and the zero-phase sequence system |Us0| are inferred from the respective control values. Subsequently, the control quantity limitations for the positive-phase sequence system (Umaxp, Uminp, ϑmaxp, ϑminp), and the negative-phase sequence system (Umaxn, Uminn, ϑmaxn, ϑminn) and optionally the zero-phase sequence system (Umax00, Uminp, ϑmax0, ϑmin0) can be determined as described with reference toFIG.5.

Here, the allowable corridors are also determined with the help of the respective factors kver. . .∈[0, 1]. For this, different sub variations are possible. On the one hand, the free areas for the respective systems can be distributed and predefined. In another realization, conditional free spaces can be used where a system (for example the positive-phase sequence system) is prioritized and the other ones result from the unused free spaces. In any case, it has to be kept in mind that the sum of all voltage differences does not leave the entire allowable voltage range.

FIG.15illustrates regulation apparatus210according to an embodiment. Optionally, the regulation apparatus210can correspond to the regulation apparatus10and can optionally comprise the features with reference toFIG.1. The regulation apparatus210comprises a limiting module230that is configured to determine a control voltage232for a current converter80in dependence on the output voltage of the current converter80. A control voltage indicator that is described by means of a first coordinate242and a second coordinate252represents the control voltage. Further, the limiting module230receives a reference voltage indicator260that is described by means of a first coordinate262and a second coordinate264and which describes the output voltage of the current converter80. The limiting module230includes a first coordinate limiting module241, configured to limit the first coordinate242of the control voltage indicator232to a first control range244around the first coordinate262of the reference voltage indicator260. Further, the limiting module230includes a second coordinate limiting module251, configured to limit the second coordinate252of the control voltage indicator232to a second control range254around the second coordinate264of the reference voltage indicator260. The first coordinate242of the control voltage indicator232and the first coordinate262of the reference voltage indicator260are related to a first coordinate axis of a coordinate system and the second coordinate252of the control voltage indicator232and the second coordinate264of the reference voltage indicator260are related to a second coordinate axis of the coordinate system. According to the embodiment ofFIG.15, the first coordinate axis and the second coordinate axis are orthogonal and rectilinear to each other. The coordinate system is, for example, a Cartesian coordinate system.

In other words, in contrary to the above-described embodiment, where the control voltage indicator32is limited to a control range determined in polar coordinates, the control range for the control voltage indicator232is determined with respect to coordinate axes that are orthogonal to each other in form of the first control range244and the second control range254. In that way, the control range can be determined in a particularly easy way. In particular, the effects described with respect to the polar coordinates that the amplitude and the angle depend on each other with respect to the first and second direction of Cartesian (or orthogonal) coordinates, e.g., dq coordinates, can be prevented. When using coordinates for the control range determination that are orthogonal to each other, the rectangular control range described with reference toFIG.4Bbut also the circular control range can be obtained in an easier way.

The regulation apparatus210is shown inFIG.15in the context of a current converter arrangement2with a current converter80and a control quantity regulation20, which can optionally be part of the regulation apparatus. The cooperation of regulation apparatus220with the control quantity regulation20and the current converter80can take place as described with respect to the above embodiments with respect toFIGS.1to14. For example, the control quantity regulation20according to the embodiment ofFIG.15can provide the set control voltage indicator232′ in orthogonal coordinates. Additionally, the regulation apparatus210can comprise the reference voltage indicator determination module78to provide the reference voltage indicator260in orthogonal coordinates.

Generally, the regulation apparatus210can optionally be supplemented by all features described with reference to the regulation apparatus110by using, instead of amplitude and angle, the first and second coordinates that are orthogonal to each other. For example, the functions of the control voltage indicator32,232of the reference voltage indicator60,260of the set control voltage indicator32′,232′ and the limiting module30,232can be identical with the exception of the used coordinates, wherein it should further be noted that the regulation apparatus210determines the first and second control range not necessarily depending on the situation but that the same can optionally also both be predetermined. Here, the first coordinate limiting module241can replace the amplitude limiting module41, the second coordinate limiting module251can replace the angle limiting module51, with respect to the control voltage indicator, the first coordinate242can replace the amplitude42and the second coordinate252can replace the angle52, the first control range244can replace the amplitude control range44, the second control range254can replace the angle control range54, a first control range determination module243can replace the amplitude control range determination module43, a second control range determination module253can replace the angle control range determination module53and, with respect to the reference voltage indicator, the first coordinate262can replace the amplitude62and the second coordinate264can replace the angle64.

For example, the regulation apparatus can comprise a first control range determination module243that determines the first control range244based on the first coordinate262of the reference voltage indicator260. Further, the regulation apparatus can comprise a second control range determination module253that determines the second control range254based on the first coordinate264of the reference voltage indicator260.

According to embodiments, the first control range determination module243adjusts the first control range244based on a first deviation limiting value (e.g.,246inFIG.16) to limit a deviation of the first coordinate242of the control voltage indicator232from the first coordinate262of the reference voltage indicator260to a first deviation limiting value. According to these embodiments, the second control range determination module253adjusts the second control range254based on a second deviation limiting value (e.g.256inFIG.16) to limit a deviation of the second coordinate252of the control voltage indicator232from the second coordinate264of the reference voltage indicator260to a second deviation limiting value.

For example, the first and the second deviation limiting value can fulfill the function as described with respect to the regulation apparatus110, for example with respect toFIG.4B. For example, the first and second deviation limiting values can state maximum deviations in the first and second direction, for example, in the direction of the first and second coordinate axis. For example, the regulation apparatus can determine the first and the second deviation limiting value depending on the situation.

For example, the first control range determination module243can determine a lower and an upper limit of the first control range, e.g., by adding and subtracting the first deviation limiting value from the first coordinate of the reference voltage indicator. Accordingly, the second control range determination module253can determine a lower and upper limit of the second control range, e.g., by adding and subtracting the second deviation limiting value from the second coordinate of the reference voltage indicator.

According to embodiments, the coordinate system of the first and second coordinate242,252can be static with respect to the reference voltage indicator260. For example, the first coordinate axis is parallel to the reference voltage indicator260and the second coordinate axis orthogonal to the reference voltage indicator.

FIG.16illustrates an example of a limiting value determination231(or control range determination231) in Cartesian coordinates, as it can be implemented in examples of the regulation apparatus210ofFIG.15. The control range determination231can represent the modules243,253ofFIG.15. According to the example ofFIG.16, the first control range244is provided in the form of an upper limiting value Uver,maxand a lower limiting value Uver,minfor the first coordinate242of the voltage indicator232. Analogously, the second control range254is provided in the form of an upper limiting value Uhor,maxand a lower limiting value Uhor,minfor the second coordinate252of the control voltage indicator232. According to the example ofFIG.16, the regulation apparatus210comprises a module266that is configured to provide the first coordinate262and the second coordinate264of the reference voltage indicator260. According to the example shown inFIG.16, the control range determination231is configured to determine the first deviation limiting value246based on the internal impedance86and to determine the lower and the upper limit of the first control range244based on the first deviation limiting value46. Further, the control range determination231according toFIG.16is configured to determine the second deviation limiting value256based on the internal impedance86and to determine the upper and the lower limit of the second control range based on the second deviation limiting value56.

In other words, the method described with respect toFIGS.2to14can be implemented also in Cartesian coordinates. Then, no decomposition and consideration of the voltage indicators in amplitude and angle has to take place, but this takes place in orthogonal components for example d, q components (vertical and horizontal). Determining the limiting values or limiting ranges becomes easier as the correct conversion for amplitude and angle can be omitted.

For this, the control voltage indicator232′,32′, for example from the grid-forming regulation, can be provided in Cartesian coordinates. In the easiest case, this can be realized by conversion based on common mathematical methods or the control/regulation of the control voltage indicator is already implemented directly in Cartesian coordinates.

FIG.17illustrates an embodiment of the regulation apparatus210. According to the example ofFIG.17, the regulation apparatus210is configured to limit the first coordinate242and the second coordinate252based on the first and second control ranges244,254as determined by means of the control range determination231ofFIG.16. In other words,FIG.17illustrates a limitation of the control voltage in Cartesian coordinates.

The different variations ofFIGS.8with12,10with11and13with14can be applied analogously, also the situation-dependent adaptation of the allowable ranges (rectangles and circles) that can be adjusted by the parameters kverand khor. The dependency of the limiting value parameters kverand khoron the actual deviation of the other components as needed, for example, in the circular range, is also maintained.

FIG.18illustrates a regulation apparatus310according to an embodiment. The regulation apparatus310is configured to provide a control quantity91for a current converter80. The current converter80comprises an intermediate circuit81. The intermediate circuit is connected to at least two intermediate circuit voltage supplies,94,95, or intermediate circuit terminals that are configured to provide an intermediate circuit voltage89. Further, the current converter80comprises a circuit node88coupled to a terminal point82of the current converter via an internal impedance86. The current converter is configured to provide a bridge voltage87(Ui) indicated by the control quantity91at the circuit node88. For this, for example, the current converter can comprise one or several half bridges83.

The regulation apparatus is configured to consider, for the control quantity91, a contribution of at least a voltage oscillation in the intermediate circuit81to the bridge voltage87. Alternatively or additionally, the regulation apparatus310is configured to consider a potential difference between a reference potential M of the bridge voltage87and a reference potential N of the output voltage85.

For example, the control signal91can be a duty cycle for a pulse with modulation by which the bridge voltage87is controlled, such as shown inFIG.9. For example, the regulation apparatus310can determine a control voltage, e.g., the control voltage32,233described with respect toFIGS.1to17, based on the output voltage85and/or one or several measurement quantities determined at the terminal point82, for example the measurement quantities84described with reference toFIG.1, and can determine the control quantity91based on the control voltage. The regulation apparatus310can consider the contribution of the voltage oscillation and/or the potential difference either when determining the control voltage or when determining the control quantity91.

As shown inFIG.18, the intermediate circuit81can optionally be configured in the form of one or several capacitor connected in series between intermediate circuit voltage supplies (cf. see alsoFIG.19). The intermediate circuit voltage89can essentially be a direct voltage. Even when the intermediate voltage89is constant, partial voltages dropping serially across the intermediate circuit89, for example a first partial voltage92between a first intermediate circuit voltage supply94and a center of the intermediate circuit and a second partial voltage93between a second intermediate circuit voltage supply95and the center of the intermediate circuit can vary in time. Here, oscillations of one or several frequencies can occur. Generally, the voltage oscillation can relate to an oscillation between a first intermediate circuit voltage supply94and a second intermediate circuit supply95or to an oscillation between one of the intermediate circuit voltage supplies94,95and a reference potential of the intermediate circuit. For example, voltage oscillations with the base frequency (the provided frequency of the output voltage) can preferably occur between one of the intermediate circuit voltage supplies and the reference potential, while voltage oscillations of higher orders of the base frequency can also occur between the intermediate circuit voltage supplies. The center of the intermediate circuit can be, for example, the center between the serial intermediate circuit capacitors. Here, the reference potential can be an average value of the potentials of the intermediate circuit voltage supplies.

The bridge voltage87is normally an alternating voltage whose frequency, i.e., the intended frequency can be referred to as fundamental oscillation. A voltage oscillation in the intermediate circuit81, for example one on the partial voltages91,92which has the frequency of the fundamental oscillation or a harmonic thereof, can result in a contribution to the bridge voltage. This contribution is, for example, an additional contribution to the bridge voltage, i.e., the one indicated by the control signal91, when it is assumed when determining the control signal that such oscillations are not present. For example, when determining the control voltage91, a control voltage indicator, e.g., the control voltage indicator32can be put in relation to one of the partial voltages92,93to consider the contribution of the voltage oscillation. Also, several voltage oscillations of different frequencies can be considered.

The output voltage85can be applied between the terminal point82and the reference potential N of the output voltage. Depending on the application case, the reference potential can be earth or a neutral conductor. The reference potential M of the bridge voltage can differ therefrom, which can have an effect on the deviation of the bridge voltage from the output voltage provided by the regulation apparatus310. It should be noted that the reference potential M does not necessarily have to be a physical potential but can also be determined theoretically, for example by a modulation method (space vector modulation). For example, in the case of a multi-phase system, cf.FIGS.19,20, the reference point M can be derived, also via the sum of the outer conductor voltages of the control voltages. Alternatively, the reference point M can be determined in relation to the intermediate circuit81, e.g., in relation to one or several of the intermediate circuit voltage supplies, for example as an average value of the potentials of the intermediate circuit voltage supplies.

Optionally, the regulation apparatus310can correspond to one of the regulation apparatuses,10,110,210described with reference toFIGS.1to17. Thus, the regulation apparatus310can be configured to limit the control voltage around a reference voltage indicator describing the output voltage85. Further, the current converter80ofFIG.18can optionally correspond to the current converter80described with reference toFIG.4A or9. The contribution of the voltage oscillation can be an example of the contribution71, which can optionally be considered in the control range determination. The potential difference between M and N can be an example of the contribution72, which can optionally be considered in the control range determination.

According to embodiments, the current converter80is a three-phase current converter, for example as described with respect toFIG.9. The regulation apparatus310can provide one control quantity91each for each of the three phases for the three-phase current converter, cf. control quantities911,912,923inFIG.19,FIG.20.

There are potentially different embodiments of a three-phase converter system. On the one hand, it can be differentiated whether the intermediate circuit is divided (by serial capacitors) and the center point is taken out or (virtually) connected to ground (cf.FIG.19). In another topology variation, a further half bridge can be implemented, whose output is connected to the center or the N conductor. Thereby, the zero current or the potential M can be controlled specifically. If, for example currents flow on the center conductor (zero sequence) into the intermediate circuit, there will be a shift of the intermediate circuit voltage. The same potential difference is applied in an unamended manner to the terminals DC+and DC−. A shift cannot be measured across the entire intermediate circuit. However, measured at DC+with respect to the center or DC−with respect to the center, there occurs an oscillation or a shift. On the (full) intermediate circuit voltage, the oscillations/shifts do not occur but exist in the intermediate circuit and can be shown, for example, by measuring the voltage at the intermediate circuit halves or can also be determined by theoretical considerations.

FIG.19illustrates an example of a configuration of a conductor converter system80with the taken-out intermediate circuit center. The taken-out intermediate circuit center can serve as reference potential M for the bridge voltage. If the taken-out intermediate circuit center is not connected to the N conductor, i.e., the potential N, the above-described potential difference can occur. The same can be determined, for example, by putting the sum of the measured outer conductor voltages851,852,853at the output, that are measured with respect to N (or are determined if the concatenated voltages are measured), in relation to the sum of the outer conductor voltages of the control voltages (e.g., the bridge voltages871,872,873).

FIG.20shows an equivalent circuit diagram of a hardware topology of an example of the current converter80. The reference point of the control voltage Ui, i.e. the bridge voltages is the center of the intermediate circuit. The same can be taken out physically, can exist virtually or can also be connected directly to the potential N. If the center is physically not localized, the potential corresponds to the virtual neutral point of the controlled three-phase voltage system (Ui1,Ui2,Ui3). Uiis compiled, for example, of the pulsed DC voltage and therefore shares the reference point. For considering of harmonics or the one or several voltage oscillations, the DC voltage to be pulsed and its reference point is decisive. If oscillation portions (particularly 50 Hz and 100 Hz) occur, the same provide, apart from the (pulse width) modulated portion, an additional contribution to the fundamental oscillation (50 Hz). This additional portion that only occurs after treating the control voltage is to be identified and considered accordingly, otherwise there will be undesired deviations between the voltage indicatorsUiandU0.

Further, depending on the implementation, the points M and N can be electrically connected or separate. In the latter case, the potential difference is also to be considered. This can be intended, for example, by modulation methods or can result by neutral point shift in unbalanced cases. This potential difference can be determined from the sum of the external conductor voltages.

In the following, further optional features as well as functions and advantages of the regulation apparatus10,110,210,310according toFIGS.1to20will be discussed.

For example, the current converter80is not limited by the innovative current limitation method of the regulation apparatus110,210ofFIGS.1to17for the normal operating range. The current converter can provide its grid-compatible contribution in a targeted manner and inherently up to a maximum limit and maintain the same as long as needed. However, the same can be free to react to a new situation. This method is suitable both for voltage drops and in case of frequency events (or phase angle events). The approach works both in the integrated grid as well as in the isolated grid.

Short-term transient current peaks of different types can additionally be remedied by pulse blocks of the semiconductors.

Common normative requirements (voltage dependent active power reduction, active power reduction in overfrequency and underfrequency, voltage-dependent reactive power provision) can also be implemented by a suitable selection of the geometrical control quantity limitations.

In contrary to other methods that try to directly treat the inverter current or at least use the inverter current to adjust the control voltage, in the regulation method presented herein, additional regulator loops or dynamics are prevented. In other words, the innovation of the inventive method lies in maintaining the controlled voltage indicator directly in a corridor for the output voltage, separated, for example, in amplitude and phase angle. This means that the actual inverter current does not have to be measured. The inventive regulation method can be implemented on all inverter-based systems that are to control a voltage behind an internal impedance. In particular, this applies for grid-forming or voltage-imprinted regulated current converters. Preferably, systems with electrical energy storage are selected, as the same can react to power changes in a flexible manner. In summary, among others, the following systems may be used: fixed battery converters, mobile battery converters (electric mobility), PV plants with supplement battery storage, wind power plants, STATCOM (Static Synchronous Compensator) with supercaps, AC grid connection of a HDVC. The method is suitable both for isolated grid applications as well as for usage in integrated operation.

FIG.21shows a flow diagram of a method1000for regulating a grid-coupled current converter, for example the current converter80. The method1000comprises a step1001of determining a control voltage32for the current converter depending on an output voltage of the current converter80. Step1001includes the steps1010to1030. Step1010includes limiting an amplitude42of a control voltage indicator32describing the control voltage to an amplitude control range44around an amplitude62of a reference voltage indicator60based on the output voltage. Step1020includes limiting an angle52of the control voltage indicator32to an angle control range54around an angle64of the reference voltage indicator60. Step1030includes situation-dependent adjusting of the amplitude control range44and the angle control range54. Step1010can be performed before, after or in parallel to step1020. Step1030can be performed before, after or between steps1010and1020.

FIG.22shows a flow diagram of a method200for regulating a grid-coupled current converter, for example the current converter80. The method1000comprises a step2001of determining a control voltage32for the current converter in dependence on an output voltage of the current converter80. Step2001includes steps2010and2020. Step2010includes liming a first coordinate242of a control voltage indicator232describing the control voltage to a first control range244around a first coordinate262of a reference voltage indicator60based on the output voltage. Step2010includes limiting a second coordinate252of the control voltage indicator232to a second control range254around a second coordinate264of the reference voltage indicator60. A first coordinate axis to which the first coordinates are related and a second coordinate axis to which the second coordinates are related are orthogonal to each other. Step2010can be performed before, after or in parallel to step2020.

FIG.23shows a flow diagram of a method300for regulating a grid-coupled current converter, for example the current converter80. The method3000includes step3001, which includes determining a control quantity91for the current converter80. Further, the method3000includes the step3002. Step3002includes providing a bridge voltage87indicated by the control quantity91at a circuit node88coupled to a terminal point82of the current converter via an internal impedance86of the current converter, wherein providing takes place based on the control quantity and an intermediate circuit voltage89of an intermediate circuit of the current converter. The method includes considering, for determining the control quantity, a contribution of at least a voltage oscillation in the intermediate circuit81to the grid voltage87and/or considering a potential difference between a reference potential M of the bridge voltage and the reference potential N of the output voltage85.

LIST OF FORMULAS

HB 1,2,3 Half bridges of the current converterZiEquivalent internal impedance of the current converterUsControl voltage as output of the current converter regulationUiResulting voltage at the half bridges of the grid-forming current converterU0Measurable output-side voltage indicator of the current converter or the grid terminal pointkpIncrease of the active power staticskqIncrease of the reactive power staticsU0Nominal value of the voltage amplitudef0Nominal value of the frequencykp′, kq′ Parameters for the phase pre-controlTaRun-up time constant (measure for inertia)ImaxConstant current amount indicated as permissibler Radius of the allowed circular area around the reference voltage indicator (starting from the equivalent internal impedance of the current converter)IoOutput current of the current converterd Portion in longitudinal direction or horizontal directionq Portion in transversal direction or vertical direction

REFERENCES

Although some aspects have been described in the context of an apparatus, it is obvious that these aspects also represent a description of the corresponding method, such that a block or device of an apparatus also corresponds to a respective method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or detail or feature of a corresponding apparatus.

Some or all of the method steps may be performed by a hardware apparatus (or using a hardware apparatus), such as a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some or several of the most important method steps may be performed by such an apparatus.

Some embodiments according to the invention include a data carrier comprising electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

The program code may, for example, be stored on a machine readable carrier.

Other embodiments comprise the computer program for performing one of the methods described herein, wherein the computer program is stored on a machine readable carrier. In other words, an embodiment of the inventive method is, therefore, a computer program comprising a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further embodiment of the inventive method is, therefore, a data carrier (or a digital storage medium or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier, the digital storage medium, or the computer-readable medium are typically tangible or non-volatile.

A further embodiment in accordance with the disclosure includes an apparatus or a system configured to transmit a computer program for performing at least one of the methods described herein to a receiver. The transmission may be electronic or optical, for example. The receiver may be a computer, a mobile device, a memory device or a similar device, for example. The apparatus or the system may include a file server for transmitting the computer program to the receiver, for example.

In some embodiments, a programmable logic device (for example a field programmable gate array, FPGA) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus. This can be a universally applicable hardware, such as a computer processor (CPU) or hardware specific for the method, such as ASIC.

In the preceding detailed description, various features have been grouped together in examples in part to streamline the disclosure. This type of disclosure should not be interpreted as intending that the claimed examples have more features than are explicitly stated in each claim. Rather, as the following claims reflect, subject matter may be found in fewer than all of the features of a single disclosed example. Consequently, the following claims are hereby incorporated into the detailed description, and each claim may stand as its own separate example. While each claim may stand as its own separate example, it should be noted that although dependent claims in the claims refer back to a specific combination with one or more other claims, other examples also include a combination of dependent claims with the subject matter of any other dependent claim or a combination of any feature with other dependent or independent claims. Such combinations are encompassed unless it is stated that a specific combination is not intended. It is further intended that a combination of features of a claim with any other independent claim is also encompassed, even if that claim is not directly dependent on the independent claim.