Patent Description:
<NPL>, relates to a state-feedback controller and observer design for grid-connected voltage source power converters with LCL-filter. An observer and state-feedback controller design for grid-connected voltage source power converters with LCL-filter under symmetric grid voltage variations is discussed where only the converter-side currents are available for feedback. The LCL-filter is modeled as lossy network including resistances, capacitance and converter-side and grid-side inductance. Observability and controllability of the system are analyzed. Controller and observer design are based on linear quadratic regulator (LQR) design with stability margin. The designed proportional-integral (PI) state-feedback controllers are extended by filter current decoupling control (FCDC) and by grid voltage feedforward compensation (GVFC). Simulation results illustrate (i) the control performance of a proportional integral and an integral state-feedback controller with and without FCDC and GVFC and (ii) the parameter sensitivity of the observer and the closed-loop system under parameter uncertainties of the inductances and the capacitance.

<NPL>, relates to high quality grid current control for LCL inverters using self-synchronizing inverter side current regulation. Current regulation of inductive-capacitive-inductive (LCL) grid-connected inverters typically require multiple current sensors to actively damp the filter resonance. Unfortunately, while inverter side current regulation avoids this issue because of its inherent LCL filter damping properties, it does not work well with distorted grids. Furthermore, both strategies require voltage sensors for grid synchronization. A current control strategy for LCL grid-connected inverters is proposed that requires only inverter side current sensors, with the grid voltage phase and capacitor current estimated from the Proportional Resonant current regulator to achieve self-synchronized indirect regulation of the grid-side current.

<CIT> relates to a three-phase grid-connected converter electric current loop AF panel control method based on twin nuclei. In order to eliminate DC component, the controller that parallel connection is composed in series by second order bandstop filter, low-pass first order filter and pi controller on the repetitive controller based on multinomial internal model, and provide the transmission function of three. The frequency response of each controller, selects each control gain of given tracking control unit and AF panel controller when according to control gain difference. <NPL>", IECON <NUM> - <NUM>th Annual Conference on IEEE Industrial.

Electronics Society, IEEE, <NUM> October <NUM> (<NUM>-<NUM>-<NUM>), pages <NUM>-<NUM>, relates to a robust active damping technique for three-phase PWM converter connected to power grid with unknown inductance. The PWM converter includes a low-pass filter in order to remove the high-frequency current that flows to the power grid. The low-pass filter is composed of two reactors and a capacitor (LCL-filter). The LCL-filter is the gain characteristic that attenuates by the high frequency band, and can eliminate the career ripple of the current. However, LCL-filter has a strong resonance characteristic. When the power grid current resonates with a high frequency, the equipments connected to the same power grid are harmfully affected. In order to control this resonance, passive damping and active damping are used. However, both methods suffer from several problems. A passive damping is a method of controlling the resonance by the damping resistance. The generation of heat by the loss of resistance becomes a problem often. The active damping is a control technology that controls the resonance without using the damping resistance. The active damping has both of the sensor method and the sensor-less method. The active damping methods with sensor require the use of an additional sensor. When active damping is used without a sensor, it becomes more sensitive to the power grid's inductance changes. Especially, in the case of an extreme increase in the power grid's inductance, problems with LCL resonance and ACR deterioration occur. When the ACR response is deteriorated, the power grid is affected by low frequency oscillation, making the power supply unstable. All equipment connected to this power grid is harmfully affected. There are few examples of low frequency oscillation in conventional active damping technologies. The proposed control method is achieved with tuning-less corresponding to the power grid's inductance.

<NPL>, relates to current control of voltage source converters connected to the grid through an LCL-filter. A current control of VSCs connected to the grid through an LCL-filter is proposed. The algorithm controls the grid current using only two sensors. Other variables are obtained with a state estimator, and the possible disturbances of the system are attenuated with active damping. The control algorithm has been proved for different disturbances, such as temporal variations in the components of the model and perturbations in the grid, and also with the linear and non-linear models.

It is the object of the present invention to simplify and improve a controller for a grid-tied power converter.

A component for dynamic resonance control of a grid-tied power converter is disclosed. A method and computer program product also perform the functions of the component. The component includes an adaptive estimator for a converter. The adaptive estimator includes a voltage input and a current input. The converter includes a switching rectifier connected to an inductor-capacitor-inductor ("LCL") filter including, for each phase of the converter, a converter inductor connected to the switching rectifier, a capacitor, and a grid inductor connected to a voltage source through a source conductor with an unknown inductance. The current input is from at least one converter inductor of a phase of the converter. The adaptive estimator includes an ideal LCL filter model and a disturbance compensator. The ideal LCL filter model is configured to generate, using a simple filter, a desired dynamic behavior of the converter and LCL filter. The component includes an LCL steady-state ("SS") compensation configured to model a steady-state effect of the LCL filter and source conductor. An output of the adaptive estimator is subtracted from an output of a feedback loop of the converter to form a preliminary voltage control signal. The preliminary voltage control signal is summed with an output of the LCL SS compensation to form a voltage control signal configured to control switching of the switching rectifier. The preliminary voltage control signal is the voltage input to the adaptive estimator.

A method for dynamic resonance control of a grid-tied power converter includes subtracting an output of an adaptive estimator from an output of a feedback loop of a converter to form a preliminary voltage control signal. The converter includes a switching rectifier and an LCL filter that includes, for each phase of the converter, a converter inductor connected to the switching rectifier, a capacitor, and a grid inductor connected to a voltage source through a source conductor with an unknown inductance. The adaptive estimator includes an ideal LCL filter model and a disturbance compensator. The ideal LCL filter model generates, using a simple filter, a desired dynamic behavior of the converter and LCL filter. The method includes inputting output current of the converter to the adaptive estimator. The output current of the converter is based on current of at least one converter inductor. The method includes summing the preliminary voltage control signal with output of an LCL SS compensation to form a voltage control signal. The voltage control signal controls switching of the switching rectifier. The LCL SS compensation models a steady-state effect of the LCL filter and source conductor. The preliminary voltage control signal is a voltage input to the adaptive estimator.

A system includes a converter and a controller for the converter. The converter includes a switching rectifier and an LCL filter that includes, for each phase of the converter, a converter inductor connected to the switching rectifier, a capacitor, and a grid inductor connected to a voltage source through a source conductor with an unknown inductance. The controller includes an adaptive estimator with a voltage input and a current input. The current input is from at least one converter inductor of a phase of the converter. The adaptive estimator includes an ideal LCL filter model and a disturbance compensator. The ideal LCL filter model is configured to generate, using a simple filter, a desired dynamic behavior of the converter and LCL filter. An LCL SS compensation is configured to model a steady-state effect of the LCL filter and source conductor. An output of the adaptive estimator is subtracted from an output of a feedback loop of the converter to form a preliminary voltage control signal. The preliminary voltage control signal is summed with an output of the LCL SS compensation to form a voltage control signal configured to control switching of the switching rectifier. The preliminary voltage control signal is the voltage input to the adaptive estimator.

In order that the advantages of the embodiments of the invention will be readily understood, a more particular description of the embodiments briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only some embodiments and are not therefore considered to be limiting of scope, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:.

The terms "including," "comprising," "having," and variations thereof mean "including but not limited to" unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise. The term "and/or" indicates embodiments of one or more of the listed elements, with "A and/or B" indicating embodiments of element A alone, element B alone, or elements A and B taken together.

Furthermore, the described features, advantages, and characteristics of the embodiments may be combined in any suitable manner. One skilled in the relevant art will recognize that the embodiments may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments.

These features and advantages of the embodiments will become more fully apparent from the following description and appended claims or may be learned by the practice of embodiments as set forth hereinafter. As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method, and/or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," "module," "estimator," "compensation," "controller," "system," etc. Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having program code embodied thereon.

Many of the functional units described in this specification have been labeled as an estimator, compensation, controller, or the like, in order to more particularly emphasize their implementation independence. For example, estimator, compensation, controller, etc. may be implemented a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. An estimator, compensation, controller, etc. may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

An estimator, compensation, controller, etc. may also be implemented in software for execution by various types of processors. An identified estimator, compensation, controller, etc. of program code may, for instance, comprise one or more physical or logical blocks of computer instructions which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified estimator, compensation, controller, etc. need not be physically located together but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the estimator, compensation, controller, etc. and achieve the stated purpose for the module.

Indeed, an estimator, compensation, controller, or the like of program code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within estimators, compensation, controllers, etc. and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set or may be distributed over different locations including over different storage devices, and may exist, at least partially, merely as electronic signals on a system or network. Where an estimator, compensation, controller, etc. or portions thereof are implemented in software, the program code may be stored and/or propagated on in one or more computer readable medium(s).

The computer readable medium may be a tangible computer readable storage medium storing the program code. The computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.

More specific examples of the computer readable storage medium may include but are not limited to a portable computer diskette, a hard disk, a random access memory ("RAM"), a read-only memory ("ROM"), an erasable programmable read-only memory ("EPROM" or Flash memory), a portable compact disc read-only memory ("CD-ROM"), a digital versatile disc ("DVD"), an optical storage device, a magnetic storage device, a holographic storage medium, a micromechanical storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, and/or store program code for use by and/or in connection with an instruction execution system, apparatus, or device.

The computer readable medium may also be a computer readable signal medium. A computer readable signal medium may include a propagated data signal with program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electrical, electromagnetic, magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport program code for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including but not limited to wireline, optical fiber, Radio Frequency (RF), or the like, or any suitable combination of the foregoing.

In one embodiment, the computer readable medium may comprise a combination of one or more computer readable storage mediums and one or more computer readable signal mediums. For example, program code may be both propagated as an electro-magnetic signal through a fiber optic cable for execution by a processor and stored on RAM storage device for execution by the processor.

Program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Python, Ruby, R, Java, Java Script, Smalltalk, C++, C sharp, Lisp, Clojure, PHP or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's controller for a converter, partly on the user's controller for a converter, as a stand-alone software package to be installed in a controller, etc..

The embodiments may transmit data between electronic devices. The embodiments may further convert the data from a first format to a second format, including converting the data from a non-standard format to a standard format and/or converting the data from the standard format to a non-standard format. The embodiments may modify, update, and/or process the data. The embodiments may store the received, converted, modified, updated, and/or processed data. The embodiments may provide remote access to the data including the updated data. The embodiments may make the data and/or updated data available in real time. The embodiments may generate and transmit a message based on the data and/or updated data in real time.

A component for dynamic resonance control of a grid-tied power converter is disclosed. A method and computer program product also perform the functions of the component. The component includes an adaptive estimator for a converter. The adaptive estimator includes a voltage input and a current input. The converter includes a switching rectifier connected to an inductor-capacitor-inductor ("LCL") filter including, for each phase of the converter, a converter inductor connected to the switching rectifier, a capacitor, and a grid inductor connected to a voltage source through a source conductor with an unknown inductance. The current input is from at least one converter inductor of a phase of the converter. The adaptive estimator includes an ideal LCL filter model and a disturbance compensator. The ideal LCL filter model is configured to generate, using a simple filter, a desired dynamic behavior of the converter and LCL filter. The component includes an LCL steady-state ("SS") compensation configured to model a steady-state effect of the LCL filter and source conductor. An output of the adaptive estimator is subtracted from an output of a feedback loop of the converter to form a preliminary voltage control signal. In some embodiments, the preliminary control signal compensates for any dynamic differences from the ideal model. The preliminary voltage control signal is summed with an output of the LCL SS compensation to form a voltage control signal configured to control switching of the switching rectifier. The preliminary voltage control signal is the voltage input to the adaptive estimator.

The output of the adaptive estimator, which is a disturbance estimate, includes any dynamic differences between an ideal model and the actual system, including unknown source inductances, nonlinearities, time variance, external disturbances, parameter perturbations, and slow degradation with age. When compensating for this disturbance in real time, the system is forced to behave with the desired dynamics of the ideal model.

In some embodiments, the LCL filter model is configured to generate the desired dynamic behavior of the converter and LCL filter with a model of an inductor that includes inductance of the converter inductor and the grid inductor without inductance of the source conductor. In other embodiments, the LCL filter model is further configured to generate the desired dynamic behavior of the converter and LCL filter with a model comprising effects of the switching rectifier. In other embodiments, the disturbance compensator includes at least proportional control. In other embodiments, an output of the ideal LCL filter model is subtracted from current in a converter inductor of at least one phase of the converter to form an input to the disturbance compensator. Output of the disturbance compensator is a disturbance estimate and the disturbance estimate is summed with the preliminary voltage control signal and a resultant signal is input to the ideal LCL filter model.

In some embodiments, compensation values of the disturbance compensator are related to compensation values of the feedback loop of the converter. In other embodiments, the component includes a scalar link that changes a proportional compensation value of the disturbance compensator by a scalar value of a proportional compensation value of the feedback loop of the converter and/or changes an integral compensation value of the disturbance compensator by a scalar value of an integral compensation value of the feedback loop of the converter. In other embodiments, compensation values of the feedback loop of the converter are derived based on the ideal LCL filter model. In other embodiments, output of the ideal LCL model is subtracted from a current reference signal to form an input to feedback compensation of the feedback loop of the converter. In other embodiments, an input to the switching rectifier is a direct current ("DC") source and the converter and LCL filter generate alternating current ("AC") current and voltage. In other embodiments, the switching rectifier is a full bridge rectifier with integrated circuit switches and the converter is bidirectional. In other embodiments, the converter is single phase, or three phase and each phase of the converter comprises an LCL filter where the converter is a three phase converter.

A method for dynamic resonance control of a grid-tied power converter includes subtracting an output of an adaptive estimator from an output of a feedback loop of a converter to form a preliminary voltage control signal. The converter includes a switching rectifier and an LCL filter that includes, for each phase of the converter, a converter inductor connected to the switching rectifier, a capacitor, and a grid inductor connected to a voltage source through a source conductor with an unknown inductance. The adaptive estimator includes an ideal LCL filter model and a disturbance compensator. The ideal LCL filter model generates, using a simple filter, a desired dynamic behavior of the converter and LCL filter. The method includes inputting output current of the converter to the adaptive estimator. The output current of the converter is based on current of at least one converter inductor. The method includes summing the preliminary voltage control signal with output of an LCL SS compensation to form a voltage control signal. The voltage control signal controlling switching of the switching rectifier. The LCL SS compensation models a steady-state effect of the LCL filter and source conductor. The preliminary voltage control signal is a voltage input to the adaptive estimator.

In some embodiments, the LCL filter model is configured to generate the desired dynamic behavior of the converter and LCL filter with a model of an inductor that includes inductance of the converter inductor and the grid inductor without inductance of the source conductor. In other embodiments, the LCL filter model is also configured to generate the desired dynamic behavior of the converter and LCL filter with a model comprising effects of the switching rectifier. In other embodiments, the method includes subtracting output of the ideal LCL model from a current reference signal and inputting a resultant signal to feedback compensation of the feedback loop of the converter. In other embodiments, the disturbance compensator includes at least proportional control. In other embodiments, the method includes subtracting an output of the ideal LCL filter model from current in a converter inductor of at least one phase of the converter to form an input to the disturbance compensator. An output of the disturbance compensator forms a disturbance estimate and the method includes summing the disturbance estimate with the preliminary voltage control signal and inputting a resultant signal to the ideal LCL filter model.

In some embodiments, the method includes setting a proportional compensation value of the disturbance compensator to be a scalar value of a proportional compensation value of the feedback loop of the converter and/or setting an integral compensation value of the disturbance compensator to be a scalar value of an integral compensation value of the feedback loop of the converter. In other embodiments, compensation values of the feedback loop of the converter are derived based on the ideal LCL filter model. In other embodiments, an input to the switching rectifier is a DC source and the converter and LCL filter generate AC current and voltage. The switching rectifier is a full bridge rectifier with integrated circuit switches and wherein the converter is bidirectional.

<FIG> is a schematic block diagram of a system <NUM> for dynamic resonance control for a single-phase grid-tied power converter according to an embodiment. <FIG> is a schematic block diagram of a system <NUM> for dynamic resonance control for a three-phase grid-tied power converter according to an embodiment. The system <NUM> with a three-phase grid-tied power converter is substantially similar to the system <NUM> of <FIG> except that the switching rectifier <NUM> and LCL filter <NUM> are three-phase and are connected to a three-phase voltage source Vsrc.

The systems <NUM>, <NUM> each include a switching rectifier <NUM> connected to an inductor-capacitor-inductor ("LCL") filter <NUM> which feeds a voltage source Vsrc through a source conductor <NUM>. The switching rectifier <NUM> may be single-phase or three-phase. The switching rectifier <NUM> and LCL filter <NUM> form a converter <NUM>, which is fed from a direct current ("DC") bus <NUM> through a conductor with line inductance Lline2. Both systems <NUM>, <NUM> of <FIG> each include a converter <NUM> with a DC input, which may be a DC bus <NUM>. In some embodiments, the DC bus <NUM> is fed from a DC source <NUM> through a conductor with a line inductance Lline. The DC source <NUM> may be a battery, solar panels, etc. In other embodiments, the DC bus <NUM> is fed from an alternating current ("AC") source <NUM> through an AC-to-DC converter <NUM>. The AC source <NUM> may be a generator or other AC source.

In some embodiments, the switching rectifier <NUM> is configured to be bi-directional so that power can flow in either direction through the converter <NUM> formed by the switching rectifier <NUM> and LCL filter <NUM>. The DC source <NUM> may be a battery, a solar panel system or other DC source. The AC source <NUM> may be a generator, a motor, a utility grid, a co-generation plant, or the like. The AC-to-DC converter <NUM>, in some embodiments, is bi-directional. In other embodiments, the AC-to-DC converter <NUM> is a motor controller. One of skill in the art will recognize other ways to provide DC power to the DC bus <NUM>.

The DC bus <NUM> includes a source capacitor Csrc, which typically stabilizes voltage on the DC bus <NUM>. In other embodiments, the DC bus <NUM> may include other elements, such as switchable resistor for controlling initial charging of the source capacitor Csrc, a snubber, transient voltage surge suppression, etc. In some embodiments, the DC bus <NUM> does not include a capacitor and a DC source <NUM> or output of an AC-to-DC converter <NUM> or other source of DC power stabilizes the DC bus <NUM>.

The switching rectifier <NUM>, in some embodiments, includes switches SW1-SW4 (or SW1-SW6) configured in a full-bridge rectifier. In other embodiments, the switching rectifier <NUM> includes switches arranged in a half-bridge rectifier. In some embodiments, the switches SW1-SW4 (or SW1-SW6) are semiconductor switches, such as a metal-oxide-semiconductor field-effect transistor ("MOSFET"), an insulated-gate bi-polar transistor ("IGBT"), and the like. In other embodiments, the switching rectifier <NUM> includes a transformer and may include other elements, such as capacitors, diodes, and the like. Control of switching of the switching rectifier <NUM> controls the converter <NUM>. Current or voltage feedback may be used in a feedback loop that changes switching of the converter <NUM>. In other embodiments, the switching rectifier <NUM> is of another topology and provides waveforms to the LCL filter <NUM> that are appropriate for filtering to produce an AC waveform.

The LCL filter includes a converter inductor Lconv, a capacitor CLCL and a grid inductor Lgrid. At the time of manufacture of the converter <NUM>, length, size, resistance and source inductance Lsource of the source conductor <NUM> are unknown. The LCL filter <NUM> with the source inductance Lsource form a resonance that varies with the source inductance Lsource. Determining parameters of a controller of the converter <NUM> may be difficult without knowing the source inductance Lsource. Typically, once the converter <NUM> is installed, a technician has to tune the controller of the converter <NUM> by adjusting parameters to compensate for the actual location of the resonant frequency formed by the LCL filter <NUM> and the source inductance Lsource of the source conductor <NUM>, which is undesirable.

In other embodiments, a control scheme that measures current in the capacitor CLCL may be used to compensate for the resonance formed when the converter <NUM> is installed. This control scheme uses a concept of a virtual resistor in series with the capacitor CLCL. However, measuring current in the capacitor CLCL introduces additional failure modes and cost. Embodiments described herein include a controller for the converter <NUM> that uses the concept of a disturbance observer to negate effects of the variable source inductance Lsource and has an additional benefit of reducing the second order effects of the LCL filter <NUM> to first order effects of an inductor.

<FIG> is a schematic block diagram of a model <NUM> of an LCL filter. The depicted model <NUM> is customized for the LCL filter <NUM> of the converter <NUM> and includes a converter voltage Vconv at the output of the switching rectifier <NUM>, a grid voltage Vgrid at the output of the converter <NUM> before the source conductor <NUM>, converter current iconv, which is the same as current in the converter inductor Lconv, grid current igrid, which is the current in the grid inductor Lgrid, voltage at the capacitor CLCL, the converter inductor Lconv and the grid inductor Lgrid. Note that the "q" variables are charge, which accumulates in the capacitor CLCL as qcap. The resistance R, in some embodiments, is parasitic resistance. The model <NUM> is a well-known LaPlace model and can be used to derive equations of the LCL filter <NUM>.

<FIG> is a schematic block diagram <NUM> depicting equations derived from the model <NUM> of <FIG>. Note that the upper equation has a numerator with a second order equation, which will result in a resonant frequency. Controlling a resonant frequency that moves based on length of the source conductor <NUM> is problematic. <FIG> is a schematic block diagram <NUM> depicting simplified equations derived from <FIG>. The numerator of the upper equation is simplified to a first order equation based on the combined inductance of the converter inductor Lconv and the grid inductor Lgrid. A physical system (e.g. "plant") that can be represented as a first-order system is much easier to manage than a second order system. While the actual plant, which is the converter <NUM>, source conductor <NUM> and voltage source vsrc, is in reality a second order system, embodiments described herein use an ideal "plant" in the form of a first order equation and a disturbance observer controller to filter out unknown second order effects to simplify control design. The diagram <NUM> of <FIG> becomes the basis for an idealized "plant" where that behaves like a first order system. A disturbance observer controller is used to derive a disturbance signal that includes source inductance Lsource of the source conductor <NUM> and a second order effect and then cancelling out the disturbance.

<FIG> is a schematic block diagram of a generic disturbance observer controller <NUM>. The physical system includes a plant P and a disturbance signal from an unknown source. The disturbance observer controller <NUM> also includes an ideal plant model Po that is simplified to reduce the plant P model and effects of the unknown disturbance to a known ideal plant model Po. The disturbance observer controller <NUM> determines an observed disturbance do, which is fed back to cancel the actual disturbance d. If the plant P is modeled as an ideal plant Po, everything different from the ideal plant model Po is treated as disturbance and rejected and the augmented system is forced to behave like the ideal plant model.

To derive the disturbance observer controller <NUM>, the physical system is modeled with an input u summed with a disturbance d and fed to the plant P, which represents a converter and other effects of a physical plant. An ideal form includes the input u summed with a disturbance estimation do and fed to the ideal plant model Po. A second step is to subtract an estimated state output xo(s) of the ideal plant model Po from the actual state output x(s) of the plant P to create an observer error signal eo(s). A third step is to at a controller, such as a proportional-integral ("PI") controller to the observer error signal eo(s), which creates the disturbance estimate signal do. A fourth step is to subtract the disturbance estimate signal do from an output of a feedback loop controlling the physical plant P. The result is that that feedback loop sees the ideal plant model Po, which includes known elements. As a result, design of the feedback loop compensator Cx is designed to control the ideal plant, which is simpler to control. In addition, because unknown elements of the physical plant P are eliminated, in some embodiments the feedback compensation Cx can be set when the converter is manufactured and does not need to be tuned after installation.

<FIG> is a schematic block diagram of an embodiment of a controller <NUM> for a dynamic resonance control for a grid-tied power converter <NUM> according to an embodiment. In some embodiments, the controller <NUM> is at least partially implemented in firmware. For example, the controller <NUM> may include firmware and a processor with signals input from the switching rectifier <NUM> and/or LCL filter <NUM> or other locations. In other embodiments, the controller <NUM> is implemented with hardware circuits. In other embodiments, the controller <NUM> is implemented with a programmable hardware device, such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

The converter <NUM> includes the switching rectifier <NUM> and LCL filter <NUM>. The controller <NUM> of <FIG> depicts a three-phase version with phases a, b and c. Note that signals of the controller <NUM> on the left are in a direct-quadrature ("d-q") domain while signals in and out of the converter <NUM> are in the time domain. Conversion between the d-q domain and time domain is well known to those of skill in the art. The voltage control signal vd,q is converted from a time domain voltage control signal va,b,c through the 2r/<NUM> block and converter current ia,b,c in the time domain is converted to a d-q domain converter current id,q with the <NUM>/2r block. A grid voltage Vgrid is fed to a phase-lock loop ("PLL") block, which is used by the 2r/<NUM> block and the <NUM>/2r block for conversion between the time domain and the d-q domain.

The grid voltage vgrid, in some embodiments, is a voltage at output terminals of the converter <NUM>, as depicted in <FIG>. The grid voltage Vgrid may be sensed using one or more wires connected to output terminals of the converter <NUM> and may be conditioned and scaled as is typical in the art. For example, the grid voltage Vgrid may fed through a transformer, voltage divider, etc. and may be conditioned using a capacitor to filter noise, etc. One of skill in the art will recognize ways to sense voltage of a converter <NUM>.

Converter current ia,b,c is also sensed and converted to the d-q domain and is represented as id,q. In the examples depicted herein, the converter current ia,b,c is sensed at the output of the switching rectifier <NUM> or through the converter inductor Lconv. Sensing may be accomplished using a current transformer, a hall-effect sensor, etc. Again, the converter current ia,b,c is conditioned for use by the controller <NUM>, for example using a filter, a snubber, a voltage divider, etc..

An adaptive estimator <NUM> of the controller <NUM> is similar to the Internal Model Form block of the disturbance observer controller <NUM> of <FIG>. The adaptive estimator <NUM> includes at least an ideal model of the LCL filter <NUM> and may include effects of the switching rectifier <NUM>. The adaptive estimator <NUM> has inputs of a preliminary voltage control signal v'd,q, which aligns with the input u except for steady-state effects of the LCL filter <NUM>, and the converter current id,q, which aligns with the actual state output x(s) of the plant P for the disturbance observer controller <NUM>. The adaptive estimator <NUM> has an output of a disturbance voltage v̂dist that roughly aligns with the disturbance estimation do of the disturbance observer controller <NUM>. The disturbance voltage v̂distcompensates for any dynamic differences from the ideal model embodied in the adaptive estimator <NUM>. The disturbance voltage v̂dist (disturbance estimate) includes any dynamic differences between the ideal model and the actual system, including unknown source inductances, nonlinearities, time variance, external disturbances, parameter perturbations, and slow degradation with age. When compensating for this disturbance in real time, the system <NUM>, <NUM> is forced to behave with the desired dynamics of the ideal model. The disturbance voltage v̂dist is subtracted from an output of feedback loop of the converter <NUM> to form the preliminary voltage control signal v'd,q.

The feedback controller within the converter <NUM> (not shown) may be proportional or proportional-integral control (represented by the P/PI block). The P/PI control is compensated using an adaptive estimator based on an ideal model of the LCL filter <NUM> and on an ideal model of the switching rectifier <NUM>, which is much simpler than compensation based on the actual LCL filter <NUM> and actual switching rectifier <NUM> with the unknown source inductance Lsource of the source conductor <NUM>. The feedback loop of the converter <NUM> includes a reference signal iconvd,q_ref that is fed into a second LCL SS comp block <NUM>.

The adaptive estimator <NUM> generates a desired dynamic behavior of the converter <NUM> using a simple filter to represent the LCL filter <NUM>. The adaptive estimator <NUM>, in some embodiments, includes a model of a simple filter to generate a desired dynamic behavior of LCL filter <NUM>. In some embodiments, the adaptive estimator <NUM> generates an ideal dynamic behavior. The simple filter, in some embodiments, is a lower order model than the actual plant, which is the converter <NUM> with an LCL filter <NUM>, the conductor <NUM>, grid voltage source Vsrc, etc. In other embodiments, the simple filter is a first order filter model of the LCL filter <NUM>. In other embodiments, the simple filter is a model of an inductor that includes inductance of the converter inductor Lconv and grid inductor Lgrid. In some embodiments, the simple filter includes effects of the switching rectifier <NUM> in addition to the LCL filter <NUM>.

In some embodiments, converter current id,q is subtracted from the output iconv_d,q* of the second LCL SS comp block <NUM> and a resulting signal is fed to the P/PI control. In other embodiments, output of the ideal LCL filter model of the adaptive estimator <NUM> generates an idealized output current of the converter <NUM> and is subtracted from the output iconv_d,q* of the second LCL SS comp block <NUM> and a resulting signal is fed to the P/PI control. Simulation results indicate that using the output of the ideal LCL filter model as input to the feedback loop of the converter <NUM> provides control of the converter similar to using output current of the converter <NUM>. A selector switch SW is depicted to point out the two options for input to the feedback loop of the converter <NUM>. The selector switch SW is not included where a designer picks one option or the other.

The preliminary voltage control signal v'd,q is summed with output Vgrid_d,q of an LCL steady-state ("SS") comp block <NUM> to form a voltage control signal vd,g, which controls switching of the switching rectifier <NUM>. The preliminary voltage control signal v'd,q is also input to the adaptive estimator <NUM>, as explained in more detail for the controller <NUM> of <FIG>. The LCL SS comp block <NUM> compensates for the steady-state effects of the LCL filter <NUM> due to a voltage difference between an output voltage of the converter <NUM> and an output voltage of the switching rectifier <NUM>. The LCL SS comp block <NUM> has a function that typically includes an input of the grid voltage vgrid, which is the output voltage of the converter <NUM>, and the converter current id,q (inputs to the LCL SS comp <NUM> not shown).

Beneficially, the adaptive estimator <NUM> negates the unknown source inductance Lsource and reduces the LCL filter <NUM> to a first-order model using a disturbance observer model specific to the converter <NUM>. Compensation (e.g. P/PI) for the feedback loop of the converter <NUM> is easier to derive because the P/PI block sees an ideal switching rectifier <NUM> and LCL filter <NUM> with a single inductor (converter inductance Lconv plus grid inductance Lgrid), which are both known values.

<FIG> is a schematic block diagram of another more detailed embodiment of a controller <NUM> for a dynamic resonance control for a grid-tied power converter <NUM> according to an embodiment. The controller <NUM> may be implemented in firmware, hardware circuits, a programable hardware device or a combination thereof and may be implemented in a similar way as the controller <NUM> of <FIG>. The controller <NUM> is a more detailed version of the controller <NUM> of <FIG> but is depicted in the d-q domain. The adaptive estimator <NUM> includes an ideal LCL filter model <NUM> that includes the converter inductance Lconv plus grid inductance Lgrid, as depicted in the numerator of the upper block of the equations of <FIG>. Other effects of the switching rectifier <NUM> are included in some embodiments.

The adaptive estimator <NUM> includes a disturbance compensator <NUM>. In some embodiments, the disturbance compensator <NUM> is a proportional-integral control, as depicted, with compensation values Ki and Kp. In other embodiments, the disturbance compensator <NUM> includes proportional control. In other embodiments, the disturbance compensator <NUM> includes proportional-integral-derivative control. Output of the disturbance compensator <NUM>, which is the disturbance voltage v̂dist, is subtracted from the output of the feedback loop of the converter <NUM>, as in the controller <NUM> of <FIG>. The disturbance voltage v̂dist is also summed with the preliminary voltage control signal v'd,q and is input to the ideal LCL filter model <NUM>, which matches with the disturbance estimate do summed with the input u and input to the ideal plant Po of the disturbance observer controller <NUM> of <FIG>.

In some embodiments, the compensation values Ki and Kp of the disturbance compensator <NUM> are related to compensation terms in the feedback loop of the converter <NUM>. For example, the compensation values Ki and Kp of the disturbance compensator <NUM> may be scaled by similar terms of a PI controller of the feedback loop of the converter <NUM> by using a scalar link <NUM> that makes changes to the compensation values Ki and Kp of the disturbance compensator <NUM> when changes to similar Ki and Kp terms of the controller of the feedback loop of the converter <NUM> are made. The scalar link <NUM>, in one embodiment, changes a proportional compensation value Kp of the disturbance compensator <NUM> by a scalar value of a proportional compensation value Kp of the feedback loop of the converter and/or changes an integral compensation value Ki of the disturbance compensator <NUM> by a scalar value of an integral compensation value Ki of the feedback loop of the converter <NUM>.

In other embodiments, the scalar link <NUM> scales the Ki and Kp terms of the disturbance compensator <NUM> using a more complex formula, such as a formula with an offset added to a product of a multiplier and a compensation value of the controller of the converter feedback loop. In other embodiments where the controller of the feedback loop of the converter <NUM> includes proportional control, the scalar link <NUM> sets the compensation values Ki and Kp of the disturbance compensator <NUM> in relation to a single Kp term of the controller of the converter feedback loop.

Using a disturbance observer controller for the converter <NUM> reduces complexity of controls for the converter <NUM> so that, in some embodiments, compensation values of the disturbance compensator <NUM> are related to compensation values of the converter feedback loop. In the embodiment, when compensation values of the controller of the converter feedback loop are adjusted, the scalar link <NUM> automatically adjusts the compensation values Ki and Kp of the disturbance compensator <NUM> so that an end user does not have to make adjustments to the compensation values Ki and Kp of the disturbance compensator <NUM>. This scalar link <NUM> reduces complexity of tuning of the controller <NUM> of the converter <NUM>.

<FIG> depicts simulation results of dynamic resonance control for a grid-tied power converter with an LCL filter for different source inductance values with open loop and closed loop results. The simulation results are an open loop forward bode plot from current command to current output. The simulation results each include a same LCL filter <NUM> with changes to the source inductance Lsource. A first trace <NUM> is for no source inductance Lsource and without the adaptive estimator <NUM>. Note that there is a resonance at around <NUM> hertz ("Hz"). A second trace <NUM> is for a source inductor Lsource of ten times the inductance of the grid inductor Lgrid and has a resonance at around <NUM>. The variation in the resonant frequency for various source inductances Lsource due to varying lengths and types of the source conductor <NUM> make compensation difficult and often requires tuning of the converter <NUM> after installation.

A third trace <NUM> is for no source inductance Lsource but with the adaptive estimator <NUM>. Note that no sizable resonance occurs in the third trace <NUM>. A fourth trace <NUM> is for a source inductor Lsource with an inductance often times the inductance of the grid inductor Lgrid and with the adaptive estimator <NUM>. Again, no resonance occurs in the fourth trace <NUM>. The simulation results contribute to validation of the idea that an adaptive estimator <NUM> improves manageability of a converter <NUM> with a switching rectifier <NUM> and an LCL filter <NUM>. Note that the adaptive estimator <NUM> does not require measurement of current of the capacitor CLCL of the LCL filter <NUM>, which is advantageous to increase reliability. Having a sensor and related hardware to measure capacitor current increases chances of failure.

<FIG> depicts closed loop simulation results of a dynamic resonance control for a grid-tied power converter <NUM> with and LCL filter <NUM>. The simulation results include a bode plot depicting closed loop results. The solid line <NUM> is for a conventional proportional-integral control. Notice that a resonant peak occurs at around <NUM>. The dashed line <NUM> includes closed loop results for a converter with an LCL filter where the feedback loop includes proportional-integral control and also includes the adaptive estimator <NUM>. Notice that the resonant peak is gone, which allows for much simpler controls.

<FIG> depicts simulation results and a Fast-Fourier transform for a converter <NUM> with an LCL filter <NUM> without compensation (upper plot (a)) and with an embodiment of a disturbance observer controller <NUM>, <NUM> depicted in <FIG> and <FIG> (lower plot (b)). The upper plot (a) depicts time-based capacitor CLCL current waveforms for <NUM> cycles on top and a Fast-Fourier transform ("FFT") analysis below for <NUM> cycles where the upper plot (a) is simulated without the adaptive estimator <NUM>. Note that the magnitude of the capacitor CLCL current waveform is over <NUM> amperes, which may damage the capacitor CLCL. The FFT analysis is based on <NUM> cycles shown in the upper waveform as hatched. The FFT analysis depicts a significant resonance point at around <NUM> with a total harmonic distortion of <NUM>%. The results indicate that compensation that does not include the adaptive estimator <NUM> or other means to dampen the resonance is unacceptable.

The lower plot (b) depicts time-based capacitor CLCL current waveforms for <NUM> cycles on top and a Fast-Fourier transform ("FFT") analysis below for <NUM> cycles where the lower plot (b) is simulated with the adaptive estimator <NUM>. Note that the magnitude of current in the capacitor CLCL is around <NUM> A, which indicates a significant reduction of current in the capacitor CLCL. The FFT analysis in the lower plot (b) shows no significant resonance at <NUM>. Note that the resonances depicted at around <NUM> are related to a switching frequency of the switching rectifier <NUM>. The lower plot (b) indicates a significant improvement in control of current in the capacitor CLCL using a method that does not include measurement of current in the capacitor CLCL.

Claim 1:
A controller (<NUM>, <NUM>) for a grid-tied power converter (<NUM>), the converter comprising a switching rectifier connected to an inductor-capacitor-inductor, LCL, filter (<NUM>) comprising, for each phase of the converter, a converter inductor connected to the switching rectifier, a capacitor, and a grid inductor connected to a voltage source through a source conductor with an unknown inductance, the controller comprising:
an adaptive estimator (<NUM>), the adaptive estimator comprising a voltage input and a current input, the current input being from at least one converter inductor of a phase of the converter, the adaptive estimator comprising an ideal LCL filter model (<NUM>) and a disturbance compensator (<NUM>), the ideal LCL filter model configured to generate, using a simple filter, a desired dynamic behavior of the converter and LCL filter, the adaptive estimator (<NUM>) generating an output current; and
an LCL steady-state, SS, compensation (<NUM>) configured to model a steady-state effect of the LCL filter and source conductor;
a selector switch (SW) for selecting one of an output current of the converter (<NUM>) and the output current of the adaptive estimator (<NUM>) as input to a feedback loop of the converter (<NUM>);
a scalar link (<NUM>) configured to adjust one or more compensation values of the disturbance compensator (<NUM>), wherein the one or more compensation values are related to compensation terms in the feedback loop of the converter; and
a second LCL SS comp block (<NUM>) configured to output a current to the feedback loop of the converter, wherein a reference current signal is fed into the second LCL SS comp block,
wherein a disturbance output voltage of the adaptive estimator (<NUM>) is subtracted from an output of the feedback loop of the converter to form a preliminary voltage control signal,
wherein the preliminary voltage control signal is summed with an output of the LCL SS compensation to form a voltage control signal configured to control switching of the switching rectifier, and
wherein the preliminary voltage control signal is the voltage input to the adaptive estimator.