Patent Description:
As disclosed herein, power generating assets may take a variety of forms and may include power generating assets which rely on renewable and/or nonrenewable sources of energy. Those power generating assets which rely on renewable sources of energy may generally be considered one of the cleanest, most environmentally friendly energy sources presently available. For example, wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The nacelle includes a rotor assembly coupled to the gearbox and to the generator. The rotor assembly and the gearbox are mounted on a bedplate support frame located within the nacelle. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy and the electrical energy may be transmitted to a converter and/or a transformer housed within the tower and subsequently deployed to a utility grid. Modern wind power generation systems typically take the form of a wind farm having multiple wind turbine generators that are operable to supply power to a transmission system providing power to a power grid.

Wind turbines can be distinguished in two types: fixed speed and variable speed turbines. Conventionally, variable speed wind turbines are controlled as current sources connected to a power grid. In other words, the variable speed wind turbines rely on a grid frequency detected by a phase locked loop (PLL) as a reference and inject a specified amount of current into the grid. The conventional current source control of the wind turbines is based on the assumptions that the grid voltage waveforms are fundamental voltage waveforms with fixed frequency and magnitude and that the penetration of wind power into the grid is low enough so as to not cause disturbances to the grid voltage magnitude and frequency. Thus, the wind turbines simply inject the specified current into the grid based on the fundamental voltage waveforms. However, with the rapid growth of the wind power, wind power penetration into some grids has increased to the point where wind turbine generators have a significant impact on the grid voltage and frequency. When wind turbines are located in a weak grid, wind turbine power fluctuations may lead to an increase in magnitude and frequency variations in the grid voltage. These fluctuations may adversely affect the performance and stability of the PLL and wind turbine current control.

As such, it may be desirable to operate asynchronous power generating assets, such as some wind turbines, as a grid-forming asset. Generally, grid-forming type converters may provide a voltage-source characteristic, where the angle and magnitude of the voltage are controlled to achieve the regulation functions needed by the grid. With this structure, current will flow according to the demands of the grid while the converter contributes to establishing a voltage and frequency for the grid. This characteristic is comparable to conventional generators based on a turbine driving a synchronous machine. Thus, the asynchronous power generating assets may share the burden of grid formation with other grid-forming sources, such as fossil-fuel-based generators, connected to the grid.

In addition to providing grid-forming power to the power grid, the power generating assets generally also must conform to certain grid requirements. For example, power generating assets may be required to offer fault-ride through (e.g. low-voltage ride through) capability. This requirement may mandate that a power generating asset stay connected to the power grid during one or more transient grid events, such as a grid fault. As used herein, the terms "grid fault," "fault," or similar are intended to cover a change in the magnitude of a grid voltage for a certain time duration. For example, when a grid fault occurs, the voltage of the system can decrease by a significant portion for a short duration (e.g., typically less than <NUM> milliseconds). In addition, grid faults may occur for variety of reasons, including but not limited to a phase conductor being connected to a ground (i.e. a ground fault), short-circuiting between phase conductors, lightning and/or windstorms, and/or accidental transmission line grounding.

In the past, the wind turbine may have been immediately disconnected in response to the voltage reduction, but as the power production of the wind turbines has increased as a percentage of the power of the power grid, the desirability for the wind turbines to remain online and ride through the transient grid events has increased. However, the voltage reduction of the transient grid event may result in the torque of the generator being significantly reduced while the rotational speed of the rotor may remain essentially unchanged. As such, when the grid voltage returns to pre-fault levels, a mismatch between the torque of the generator and the inertia of the rotor may result in undesirable torsional vibrations in the drivetrain of the wind turbine. The torsional vibrations may manifest as oscillations in the power produced by the wind turbine which exceed certain power grid limits.

Typically, power generating assets may be equipped with damping systems, such as drivetrain dampers, which may generate a generator setpoint configured to rapidly damp the oscillations resulting from the transient grid event. However, when operating as a grid-forming asset, the commands from the damping system may interfere with, or be negated by, the setpoint commands of the power generating asset seeking to develop the grid voltage and frequency required to form the grid power. <CIT> describes a stator frequency control method of a DFIG system.

Thus, the present disclosure is directed to a system and method for addressing drivetrain damper oscillations while providing grid-forming control to the power grid to address the aforementioned issues.

In one aspect, the present disclosure is directed to a method for providing grid-forming control of a double-fed generator connected to a power grid. The method may include determining, via a frequency module of the controller, a stator-frequency error for the generator. The method may also include determining, via a controller shaping module of the frequency module, a torsional component and a stator component of the stator-frequency error. The torsional component may correspond to a drivetrain torsional vibration frequency. Additionally, the method may include determining, via the frequency module, a power output requirement for the generator based, at least in part, on the stator component of the stator-frequency error. The power output requirement may be combined, via the frequency module, with a damping power command to develop a consolidated power requirement for the generator. The damping power command may be generated in response to the torsional vibration frequency. Based, at least in part, on the consolidated power requirement, the controller may determine at least one control command for the generator. Additionally, the method may include changing an operating state of the generator in response to the control command(s) so as to output a grid-forming voltage and frequency.

In an embodiment, the stator-frequency error may include a difference between a reference frequency and a stator-output frequency.

In an additional embodiment, determining the control command(s) for the generator may include determining, via the controller, a rotor voltage setpoint based, at least in part, on the consolidated power requirement.

In a further embodiment, the method may include monitoring, via the controller, a three-phase stator voltage and current of the generator. Additionally, the method may include transforming the three-phase stator voltage and current via an abc-to-dq transfer module of the controller to a d-q reference frame so as to determine a d-component and a q-component for the current and voltage. The method may also include determining, via a phase locked loop module of the controller, the stator-output frequency based on the d-component of the stator voltage.

In yet a further embodiment, the stator component of the stator-output frequency may include a direct current (DC) value and the torsional component of the stator-output frequency may include a sinusoidal frequency.

In an embodiment, determining the torsional component and the stator component of the stator-frequency error may also include establishing, via the frequency module, a gain value of zero at the torsional vibration frequency, and establishing, via the frequency module, a non-zero gain value for values of the stator-frequency error which do not correspond to the torsional vibration frequency.

In an additional embodiment, the non-zero gain value may have a maximal value when the stator-frequency error has a minimal value and may decrease with an increase in the stator-frequency error.

In a further embodiment, the method may include determining, via a voltage module of the controller, a stator-voltage error for the generator. The stator-voltage error may include a difference between a reference voltage and a stator-output voltage. The stator-output voltage may be the q-component of the stator voltage. Additionally, the method may include determining, via the voltage module, a required rotor voltage d-component based, at least in part, on the stator-voltage error.

In yet a further embodiment, determining the control command(s) for the generator may include determining, via the frequency module, a required rotor voltage q-component based, at least in part, on the consolidated power requirement. Additionally, the method may include combining, via a dq-to-abc transform module of the controller, the required rotor voltage d-component and the required rotor voltage q-component to generate a rotor voltage setpoint.

In yet a further embodiment, the method may include receiving, via the controller, the reference frequency. The reference frequency may correspond to an output frequency of the generator required to support the frequency of the power grid. Additionally, the method may include receiving, via the controller, the reference voltage. The reference voltage may correspond to an output voltage magnitude of the generator required to support the power grid.

In an embodiment, the damping power command may be generated by a drivetrain-damping module configured to damp torsional vibrations resulting from a transient grid event.

In an additional embodiment, the method may include detecting, via the controller, an oscillation in a power output of the wind turbine during a transient-event recovery phase following the transient grid event. In response to detecting the oscillation, the method may include storing at least a portion of the oscillatory power in an energy storage device operably coupled to the generator.

In another aspect, the present disclosure is directed to a system for operating a power generating asset so as to provide grid forming control. The system may include a double-fed generator connected to a power grid, and a controller communicatively coupled to the power converter. The controller may include at least one processor and a plurality of modules configured to perform a plurality of operations. The plurality of operations may include any of the operations and/or features described herein.

Generally, the present disclosure is directed to systems and methods for providing grid-forming control of a double-fed generator of a power generating asset connected to a power grid. In particular, the systems and methods disclosed herein may be employed to address coordinate the damping of drivetrain oscillations while still providing the grid frequency and voltage required for grid forming. When configured to support grid forming, as opposed to being grid-following, a power generating asset may be provided with a reference (e.g. target) frequency and voltage for the power output of the power generating asset.

In order to provide the required frequency and/or voltage, a controller may, via a number of modules, compare a frequency of the stator output to the reference frequency and/or the stator voltage to the reference voltage. When the stator frequency and/or the stator voltage deviate from the corresponding reference value, the controller may generate a setpoint command. The setpoint command may affect the rotor of the generator thereby the output of the stator to bring the output into alignment with the reference frequency so as to support grid forming.

In addition to supporting grid forming, when the power generating asset encounters a transient grid event, a torsional vibration may develop during a recovery phase. It may be desirable to damp the torsional vibration to limit power fluctuations in the power delivered to the grid. In order to damp the torsional vibration, the power generating asset may be equipped with a module, such as a drivetrain-damping module which may generate a torque set point (e.g. a damping power command) for the generator in response to the detection of a transient grid event.

The torsional vibration may, however, be reflected in the stator-output frequency. As the controller may be configured to provide grid-forming control, which may be based on the deviation in the frequency relative to the reference frequency, the controller may establish at least one control command in reaction to the detected frequency deviation. As such, without the employment of the systems and methods disclosed herein, the controller may generate at least one control command which may conflict with, override, and/or negate the torque setpoint generated by the drivetrain-damping module. Such an interaction may result in the inadequate damping of the torsional vibration.

To facilitate the integration of the damping power command(s) related to the damping of the torsional vibration with the control command(s) directed at providing the grid forming frequency, the systems and methods disclosed herein may determine a frequency error corresponding differences between the reference frequency and the stator frequency. The controller may then determine the portion of the frequency error attributed to the torsional vibration (e.g. a torsional component to be damped by the damping module) and the portion attributable to the stator (e.g. a stator component to be brought into alignment with the reference frequency). A power output requirement may be determined based on the stator component of the frequency error. Once the power output requirement is determined based on stator component of the frequency error, the damping power command from the damping module may be added to the power output requirement to produce a consolidated power requirement for the generator. The controller may then utilize the consolidated power requirement to determine the control command(s) for the generator. It should be appreciated that combining of the damping power command with the power output requirement based on the stator component may preclude any conflict, overriding, and/or negation of the damping power command by the control command(s).

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a power generating asset <NUM> according to the present disclosure. As shown, the power generating asset <NUM> may be configured as a wind turbine <NUM>. In an additional embodiment, the power generating asset <NUM> may, for example, be configured as a solar power generating asset, a hydroelectric plant, a fossil fuel generator, and/or a hybrid power generating asset.

When configured as a wind turbine <NUM>, the power generating asset <NUM> may generally include a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM>, mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated embodiment, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. Each rotor blade <NUM> may be spaced about the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub <NUM> may be rotatably coupled to an electric generator <NUM> (<FIG>) of an electrical system <NUM> (<FIG>) positioned within the nacelle <NUM> to permit electrical energy to be produced.

The wind turbine <NUM> may also include a controller <NUM> centralized within the nacelle <NUM>. However, in other embodiments, the controller <NUM> may be located within any other component of the wind turbine <NUM> or at a location outside the wind turbine. Further, the controller <NUM> may be communicatively coupled to any number of the components of the wind turbine <NUM> in order to control the components. As such, the controller <NUM> may include a computer or other suitable processing unit. Thus, in several embodiments, the controller <NUM> may include suitable computer-readable instructions that, when implemented, configure the controller <NUM> to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals.

Referring now to <FIG>, wherein an exemplary electrical system <NUM> of the power generating asset <NUM> is illustrated. As shown, the generator <NUM> may be coupled to the rotor <NUM> for producing electrical power from the rotational energy generated by the rotor <NUM>. Accordingly, in an embodiment, the electrical system <NUM> may include various components for converting the kinetic energy of the rotor <NUM> into an electrical output in an acceptable form to a connected power grid <NUM>. For example, in an embodiment, the generator <NUM> may be a doubly-fed induction generator (DFIG) having a stator <NUM> and a generator rotor <NUM>. The generator <NUM> may be coupled to a stator bus <NUM> and a power converter <NUM> via a rotor bus <NUM>. In such a configuration, the stator bus <NUM> may provide an output multiphase power (e.g. three-phase power) from a stator of the generator <NUM>, and the rotor bus <NUM> may provide an output multiphase power (e.g. three-phase power) of the generator rotor <NUM> of the generator <NUM>. Additionally, the generator <NUM> may be coupled via the rotor bus <NUM> to a rotor side converter <NUM>. The rotor side converter <NUM> may be coupled to a line-side converter <NUM> which, in turn, may be coupled to a line-side bus <NUM>.

In an embodiment, the rotor side converter <NUM> and the line-side converter <NUM> may be configured for normal operating mode in a three-phase, pulse width modulation (PWM) arrangement using insulated gate bipolar transistors (IGBTs) as switching devices <NUM>. Other suitable switching devices may be used, such as insulated gate commuted thyristors, MOSFETs, bipolar transistors, silicone-controlled rectifiers, and/or other suitable switching devices. The rotor side converter <NUM> and the line-side converter <NUM> may be coupled via a DC link <NUM> across a DC link capacitor <NUM>.

In an embodiment, the power converter <NUM> may be coupled to the controller <NUM> configured as a converter controller <NUM> to control the operation of the power converter <NUM>. For example, the converter controller <NUM> may send control commands to the rotor side converter <NUM> and the line-side converter <NUM> to control the modulation of switching elements used in the power converter <NUM> to establish a desired generator torque setpoint and/or power output.

As further depicted in <FIG>, the electrical system <NUM> may, in an embodiment, include a transformer <NUM> coupling the power generating asset of <NUM> to the power grid <NUM> via a point of interconnect (POI) <NUM>. The transformer <NUM> may, in an embodiment, be a <NUM>-winding transformer which includes a high voltage (e.g. greater than <NUM> KVAC) primary winding <NUM>. The high voltage primary winding <NUM> may be coupled to the power grid <NUM>. The transformer <NUM> may also include a medium voltage (e.g. <NUM> KVAC) secondary winding <NUM> coupled to the stator bus <NUM> and a low voltage (e.g. <NUM> VAC, <NUM> VAC, etc.) auxiliary winding <NUM> coupled to the line bus <NUM>. It should be appreciated that the transformer <NUM> can be a three-winding transformer as depicted, or alternatively, may be a two-winding transformer having only a primary winding <NUM> and a secondary winding <NUM>; may be a four-winding transformer having a primary winding <NUM>, a secondary winding <NUM>, and auxiliary winding <NUM>, and an additional auxiliary winding; or may have any other suitable number of windings.

In an embodiment, the electrical system <NUM> may include various protective features (e.g. circuit breakers, fuses, contactors, and other devices) to control and/or protect the various components of the electrical system <NUM>. For example, the electrical system <NUM> may, in an embodiment, include a grid circuit breaker <NUM>, a stator bus circuit breaker <NUM>, and/or a line bus circuit breaker <NUM>. The circuit breaker(s) <NUM>, <NUM>, <NUM> of the electrical system <NUM> may connect or disconnect corresponding components of the electrical system <NUM> when a condition of the electrical system <NUM> approaches a threshold (e.g. a current threshold and/or an operational threshold) of the electrical system <NUM>.

As depicted in <FIG>, in an embodiment, the power generating asset <NUM> may include at least one operational sensor <NUM>. The operational sensor(s) <NUM> may be configured to detect a performance of the power generating asset <NUM>, e.g. in response to the environmental condition. In an embodiment, the operational sensor(s) <NUM> may be configured to monitor a plurality of electrical conditions, such as slip, stator voltage and current, rotor voltage and current, line-side voltage and current, DC-link charge and/or any other electrical condition of the power generating asset.

It should also be appreciated that, as used herein, the term "monitor" and variations thereof indicates that the various sensors of the power generating asset <NUM> may be configured to provide a direct measurement of the parameters being monitored or an indirect measurement of such parameters. Thus, the sensors described herein may, for example, be used to generate signals relating to the parameter being monitored, which can then be utilized by the controller <NUM> to determine a condition or response of the power generating asset <NUM>.

Referring to <FIG>, multiple embodiments of a system <NUM> for providing grid-forming control of the generator <NUM> of the power generating asset <NUM> according to the present disclosure are presented. As shown particularly in <FIG>, a schematic diagram of one embodiment of suitable components that may be included within the system <NUM> is illustrated. For example, as shown, the system <NUM> may include the controller <NUM> communicatively coupled to the sensor(s) <NUM>. Further, as shown, the controller <NUM> includes one or more processor(s) <NUM> and associated memory device(s) <NUM> configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like and storing relevant data as disclosed herein). Additionally, the controller <NUM>, may also include a communications module <NUM> to facilitate communications between the controller <NUM>, and the various components of the power generating asset <NUM>. Further, the communications module <NUM> may include a sensor interface <NUM> (e.g., one or more analog-to-digital converters) to permit signals transmitted from the sensor(s) <NUM> to be converted into signals that can be understood and processed by the processors <NUM>. It should be appreciated that the sensor(s) <NUM> may be communicatively coupled to the communications module <NUM> using any suitable means. For example, the sensor(s) <NUM> may be coupled to the sensor interface <NUM> via a wired connection. However, in other embodiments, the sensor(s) <NUM> may be coupled to the sensor interface <NUM> via a wireless connection, such as by using any suitable wireless communications protocol known in the art. Additionally, the communications module <NUM> may also be operably coupled to an operating state control module <NUM> configured to change at least one turbine operating state of the power generating asset <NUM>, such as an operating state of the generator <NUM>.

As used herein, the term "processor" refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) <NUM> may generally comprise memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) <NUM> may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) <NUM>, configure the controller <NUM> to perform various functions including, but not limited to, determining a power output requirement for the generator <NUM> based on the stator component of the stator-frequency error and combining the power output requirement with a damping power command to generate a consolidated power requirement for the generator <NUM> as described herein, as well as various other suitable computer-implemented functions.

In an embodiment, the controller <NUM> may employ a frequency module <NUM> to develop the required frequency component of the grid-forming control. For example, the frequency module <NUM> may receive a reference frequency <NUM> and a stator-output frequency <NUM>. The reference frequency <NUM> may correspond to the frequency of the power output of the power generating asset <NUM> necessary to provide the required grid-forming (e.g., the output frequency of the generator <NUM> required to support the frequency of the power grid <NUM>). A difference between the reference frequency <NUM> and the stator-output frequency <NUM> may be utilized to determine a stator-frequency error <NUM> a required power output for the stator <NUM>. The required power output may be converted to a component of current and compared to a corresponding current component for the stator <NUM>. In an embodiment, the frequency module <NUM> may utilize the comparison of the current component to the corresponding current component of the stator <NUM> to develop a rotor voltage q-component <NUM>, which may be utilized to generate such a rotor voltage setpoint <NUM> as may be necessary to deliver the required grid-forming control.

In an additional embodiment, the controller <NUM> may employ a voltage module <NUM> determine a rotor voltage d-component <NUM> corresponding to a difference between a reference voltage <NUM> and a stator-output voltage <NUM>. The reference voltage <NUM> may correspond to the voltage of the power output of the power generating asset <NUM> necessary to provide the required grid-forming (e.g., the output voltage magnitude of the generator <NUM> required to support the power grid <NUM>). In an embodiment, the difference between the reference voltage <NUM> and the stator-output voltage <NUM> may be utilized to determine a reference reactive power for the stator <NUM> of the generator <NUM>. The reference reactive power may be converted to a component of current and compared to a corresponding current component for the stator <NUM>. In an embodiment, the voltage module <NUM> may utilize the comparison of the current components to develop the rotor voltage d-component <NUM>. In an embodiment, the rotor voltage d-component <NUM> and the rotor voltage q-component <NUM> may be combined to generate the rotor voltage setpoint <NUM> necessary for the delivery of grid-forming control.

In an embodiment, the controller <NUM> may employ the frequency module <NUM> to determine a stator-frequency error <NUM> for the generator <NUM>. As depicted at <NUM>, in an embodiment, a controller shaping module <NUM> of the frequency module <NUM> may be employed by the system <NUM> to determine the frequency components of the stator-frequency error <NUM>. Accordingly, the controller shaping module <NUM> may determine at least a stator component <NUM> of the stator-frequency error <NUM>. For example, in an embodiment, the controller shaping module <NUM> may identify and/or filter out a torsional component <NUM> of the stator-frequency error <NUM>, therefore determining the stator component <NUM>. Based on the stator component <NUM> of the stator-frequency error <NUM>, the frequency module <NUM> may determine a power output requirement <NUM> for the generator <NUM>. The frequency module <NUM> may combine the power output requirement <NUM> with a damping power command <NUM>, which may be generated in response to the drivetrain torsional vibration frequency <NUM>, to develop a consolidated power requirement <NUM> for the generator <NUM>. The controller <NUM> may, in an embodiment, determine at least one control command <NUM> for the generator <NUM> based, at least in part, on the consolidated power requirement <NUM>. For example, in an embodiment, determining the control command(s) <NUM> may include determining the rotor voltage setpoint <NUM> based, at least in part, on the consolidated power requirement <NUM>. In response to the control command(s) <NUM> (e.g. the rotor voltage setpoint <NUM>), an operating state <NUM> of the generator may be changed/altered in order to output a grid-forming voltage and frequency.

As previously mentioned, in an embodiment, the system <NUM> may employ the frequency module <NUM> to determine a difference between the reference frequency for the generator <NUM> (e.g. the reference frequency for the stator <NUM> desirable for grid-forming) and the actual stator-output frequency <NUM>. In an embodiment, the stator-output frequency <NUM> may be obtained directly from the operational sensor(s) <NUM> and/or computed from additional parameters of the power generating asset <NUM> monitored by the operational sensor(s) <NUM>.

In an embodiment, wherein the stator-output frequency <NUM> may be computed, the controller <NUM> may monitor a three-phase stator voltage <NUM>. The three-phase stator voltage <NUM> may be expressed in terms of an abc-reference frame. As depicted at <NUM>, the controller <NUM> may employ an abc-to-dq transfer module <NUM>, to transform the three-phase stator voltage/current <NUM> from the abc-reference frame to a dq-reference frame. The transformation at step <NUM> may determine a d-component <NUM> and a q-component <NUM> for the stator current/voltage.

As disclosed herein, the controller <NUM> may, in an embodiment, include a phase locked loop module <NUM>. As depicted at <NUM>, the system <NUM> may, thus, employ the phase locked loop module <NUM> to determine the stator-output frequency <NUM>. In such an embodiment, the stator-output frequency <NUM> may be based on the d-component <NUM> of the three-phase stator voltage <NUM>.

In an embodiment the stator component <NUM> of the stator-output frequency <NUM> may be a DC value. However, in an embodiment wherein a torsional vibration <NUM> may be reflected in the stator-output frequency <NUM>, the torsional component <NUM> of the frequency error <NUM> may have a sinusoidal frequency. Accordingly, in an embodiment, to determine the stator component <NUM> of the stator-frequency error <NUM>, the frequency module <NUM> (via the controller shaping module <NUM>) may, establish a gain value of zero at the torsional vibration frequency <NUM>. Similarly, as depicted at <NUM>, the frequency module <NUM> may establish a non-zero gain value for values of the stator-frequency error which do not correspond to the torsional vibration frequency <NUM>.

In an embodiment, the non-zero gain value may have a maximal value when the stator-frequency error <NUM> has a minimal value and may decrease with an increase in the stator-frequency error <NUM>. For example, in an embodiment wherein the difference between the reference frequency <NUM> and the stator-output frequency <NUM> is relatively minor, a high likelihood may exist that the stator-output frequency <NUM> may be out of phase with the reference frequency <NUM>. In such an embodiment, it may be desirable to modify the rotor voltage setpoint <NUM> so as to bring the power output of the generator <NUM> into alignment with the required grid-forming parameters. However, a large difference between the frequencies <NUM>, <NUM> may indicate an increased likelihood that at least a portion of the stator-frequency error <NUM> should be damped or addressed via other control actions.

It should be appreciated that the torsional vibration frequency <NUM> may be a known value for the power generating asset <NUM> based on the structural and/or material characteristics of the power generating asset <NUM>. It should further be appreciated that the establishment of a gain value of zero at the torsional vibration frequency <NUM> may preclude the utilization of the torsional vibration frequencies <NUM> for the determination of the power output requirement <NUM> for the stator <NUM>.

In addition to the utilization of the frequency module, the system <NUM> may also include the voltage module <NUM>. Accordingly, in an embodiment, the voltage module <NUM> may be utilized to determine a stator-voltage error <NUM> for the generator <NUM>. The stator-voltage error <NUM> may correspond to a difference between the reference voltage <NUM> and the stator-output voltage <NUM>. In an embodiment, the stator-output voltage may be the q-component <NUM> of the three-phase stator voltage <NUM>. Additionally, the voltage module <NUM> may determine the required voltage d-component <NUM> based, at least in part, on the stator-voltage error <NUM>.

As disclosed herein, in order to determine the control command(s) <NUM>, the system <NUM> may, via the frequency module <NUM>, determine the rotor voltage q-component <NUM> based, at least in part, on the consolidated power requirement <NUM>. In an embodiment, rotor voltage q-component <NUM> determined by the frequency module <NUM> may be combined with the rotor voltage d-component <NUM> determined by the voltage module <NUM>. For example, in an embodiment, the rotor voltage q-component <NUM> and the rotor voltage d-component <NUM> may be combined via a dq-to-abc transform module <NUM> of the controller <NUM>. As depicted at <NUM>, the dq-to-abc transform module <NUM> may combine and transform the rotor voltage q-component <NUM> and the rotor voltage d-component <NUM> to generate the rotor voltage setpoint <NUM> expressed in the abc-reference frame.

In an embodiment, the system <NUM> may include a drivetrain-damping module <NUM>. As such, in an embodiment wherein the controller <NUM> detects, for example, a transient grid event <NUM>, the drivetrain-damping module <NUM> may be configured to damp any resulting torsional vibrations <NUM>. In order to damp the torsional vibrations <NUM>, the drivetrain-damping module <NUM> may generate a damping power command <NUM>. The damping power command <NUM> may, for example, establish an increased torque setpoint for the generator <NUM> relative to a torque setpoint prior to the transient grid event <NUM>. It should be appreciated that the damping power command <NUM> may have a proportional relationship to the torsional component <NUM> of the frequency error <NUM>.

It should further be appreciated that the damping power command <NUM> may be directed to achieving the desired level of damping without consideration for the reference frequency <NUM>. As such, the development of the consolidated power requirement <NUM> via the addition of the power output requirement <NUM> (based on the stator component <NUM> of the frequency error <NUM>) and the damping power command <NUM> (determined based on a damping requirement of the torsional vibrations <NUM>) may facilitate the simultaneous addressing of both the grid-forming control requirements and the damping requirements of the power generating asset <NUM>.

In an additional embodiment, the controller <NUM> may be configured to receive data indicative of a power output parameter <NUM> of the power generating asset <NUM>. Based on the power output parameter <NUM>, the controller <NUM> may detect a power output oscillation <NUM> in the power output of the power generating asset <NUM> during a transient-event recovery phase following the transient grid event <NUM>. As depicted at <NUM>, in response to detecting the power output oscillation <NUM>, the controller <NUM> may be configured to store at least a portion of the oscillatory power in an energy storage device <NUM> operably coupled to the generator <NUM>. For example, in an embodiment, the controller <NUM> may store a portion of the oscillatory power exceeding a pre-transient event power level so as to preclude the transmission of the oscillatory power to the power grid <NUM>.

Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Claim 1:
A method for providing grid-forming control of a double-fed generator connected to a power grid, the method comprising:
determining (<NUM>), via a frequency module of a controller, a stator-frequency error for the generator;
determining (<NUM>), via a controller shaping module of the frequency module, a torsional component (<NUM>) and a stator component (<NUM>) of the stator-frequency error, wherein the torsional component corresponds to a drivetrain torsional vibration frequency;
determining (<NUM>), via the frequency module, a power output requirement for the generator based, at least in part, on the stator component of the stator-frequency error;
combining, via the frequency module, the power output requirement with a damping power command (<NUM>) to develop (<NUM>) a consolidated power requirement for the generator, wherein the damping power command is generated in response to the drivetrain torsional vibration frequency;
determining (<NUM>), via the controller, at least one control command for the generator, based, at least in part, on the consolidated power requirement; and
changing (<NUM>) an operating state of the generator in response to the at least one control command so as to output a grid-forming voltage and frequency.