System and method for mitigating subsynchronous oscillations in inverter-based resources

Abstract

A method for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection includes determining, via a controller, one or more rotor current commands for a power converter of the inverter-based resource. The method further includes applying, via a software module of the controller, the at least one stator current component to the one or more rotor current commands to provide active damping to mitigate subsynchronous power oscillations in the inverter-based resources. Further, the method includes determining, via the controller, at least one voltage command for the inverter-based resource from the one or more rotor current commands and the at least one stator current component. Further, the method includes controlling, via a controller, an inverter-based resource based at least in part on the voltage command.

Description

Technical Field

[0001] The present disclosure relates generally to inverter-based resources such as wind turbine power systems, and more particularly to systems and methods for mitigating subsynchronous oscillations in inverter-based resources connected to a series compensation network for grid forming and grid tracking. Background Art

[0002] Wind power is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines have gained increasing attention in this regard. Modern wind turbines typically include a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture the kinetic energy of the wind using the known airfoil principle. For example, the rotor blades typically have an airfoil cross-sectional profile so that during operation, air flows over the blades, creating a pressure difference between the two sides. As a result, a lift force directed from the pressure side to the suction side acts on the blades. The lift force generates a torque on the main rotor shaft, which is typically meshed with a generator for generating electricity.

[0003] Wind turbines can be divided into two types: fixed speed turbines and variable speed turbines. Traditionally, variable speed wind turbines are controlled as current sources connected to the power grid. In other words, variable speed wind turbines rely on the grid frequency detected by a phase locked loop (PLL) as a reference and inject a specified amount of current into the grid. Traditional current source control of wind turbines is based on the following assumptions: the grid voltage waveform is a basic voltage waveform with a fixed frequency and amplitude, and the penetration of wind power into the grid is low enough so as not to interfere with the grid voltage amplitude and frequency. Therefore, the wind turbine simply injects a specified current into the grid based on the basic voltage waveform. However, with the rapid growth of wind power, the penetration of wind power into some grids has increased to the extent that wind turbine generators have a significant impact on the grid voltage and frequency. When a wind turbine is located in a weak grid, wind turbine power fluctuations may result in an increase in the amplitude and frequency changes of the grid voltage. These fluctuations may adversely affect the performance and stability of the PLL and wind turbine current control.

[0004] Many existing renewable power generation converters, such as doubly-fed wind turbine generators, operate in a "grid tracking" mode. Grid tracking devices utilize a fast current regulation loop to control the active and reactive power exchanged with the grid. More specifically, FIG. 1 illustrates the basic elements of the main circuit and converter control structure for a grid tracking doubly-fed wind turbine generator. As shown, an active power reference to the converter is generated by an energy source regulator (e.g., a turbine control portion of a wind turbine). This is transmitted as a torque reference, which represents the lesser of the maximum power available from the energy source at that moment, or a reduction command from a higher-level grid controller. The converter then controls a current reference that determines the active component of the current to achieve the desired torque. Therefore, the doubly-fed wind turbine generator includes the functionality of managing voltage and reactive power in a manner that generates a command for the reactive component of the current. A wide bandwidth current regulator then generates a command for the voltage to be applied to the system by the converter so that the actual current closely tracks the command.

[0005] Alternatively, a grid-forming converter provides a voltage source characteristic in which the angle and amplitude of the voltage are controlled to achieve the regulation function required by the grid. With this structure, current will flow according to the needs of the grid, while the converter helps to establish the voltage and frequency for the grid. This characteristic is comparable to that of a conventional generator based on a turbine driving a synchronous machine. Therefore, a grid-forming source must include the following basic functions: (1) support grid voltage and frequency (both real and reactive) for any current flow within the rating of the device; (2) prevent operation beyond the voltage or current capability of the device by allowing the grid voltage or frequency to change without disconnecting the device (disconnection is only allowed when the voltage or frequency is outside the limits established by the grid entity); (3) remain stable for any grid configuration or load characteristics, including serving isolated loads or connecting to other grid-forming sources, and switching between such configurations; (4) share the total load of the grid among other grid-forming sources connected to the grid; (5) ride through both major and minor grid disturbances, and (6) meet requirements (1)-(5) without requiring rapid communication with other control systems present in the grid, or externally generated logic signals related to changes in grid configuration.

[0006] In the early 1990s, basic control structures for achieving the above-mentioned grid forming goals were developed and field-proven for battery systems (e.g., see U.S. Patent No. 5,798,633, entitled “Battery Energy Storage Power Conditioning System”). Applications to full-converter wind generators and solar generators are disclosed in U.S. Patent No. 7,804,184, entitled “System and Method for Control of a Grid Connected Power Generating System” and U.S. Patent No. 9,270,194, entitled “Controller for controlling a power converter”. Applications to grid forming control for doubly-fed wind turbine generators are disclosed in PCT / US2020 / 013787, entitled “System and Method for Providing Grid-Forming Control for a Doubly-Feb Wind Turbine Generator”.

[0007] To be effective, grid forming (GFM) inverter based resources (IBR) must be able to maintain internal voltage phasors that do not move rapidly when there are changes in grid conditions, such as sudden addition / removal of loads, opening or closing of grid connections that cause phase jumps and / or rapid changes in frequency. In other words, the power from the grid forming resources must be able to change suddenly to stabilize the grid, with subsequent slow reset of power being commanded from higher level control functions. In addition, the grid forming resources must be able to quickly implement power limits that exist due to constraints on the power processing portion of the device, such as DC voltage / current in batteries, solar arrays, and / or wind power generation systems. Such a response is required for severe disturbances on the grid, such as faults where power limits will be dynamically adjusted to coordinate with grid conditions for safe recovery from the fault. In addition, the grid forming resources should be able to quickly track changes in commands from higher level controls, for example, for damping mechanical vibrations in wind turbines. However, such requirements may be difficult to achieve.

[0008] In addition, at least some known utility grids include one or more series compensated transmission lines. Doubly fed induction generator (DFIG) wind turbines connected to series compensated transmission lines are susceptible to subsynchronous oscillations. Therefore, in some instances, under subsynchronous conditions, the control system associated with the DFIG wind turbine may present a negative resistance to the grid. This is primarily caused by the high bandwidth rotor current control loop, which increases the effective rotor side resistance. Unexpected subsynchronous active power oscillations can lead to instability and equipment damage in the system. This subsynchronous phenomenon involving the grid, DFIG, power converter, and control loop can effectively disconnect the wind turbine from the grid.

[0009] In view of the foregoing, improved systems and methods that address the aforementioned problems would be welcomed in the art.Accordingly, the present disclosure is directed to systems and methods for mitigating subsynchronous power oscillations in inverter-based resources for grid forming and grid tracking connected to a series compensation network. Summary of the invention

[0010] The aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned by practice of the invention.

[0011] In one aspect, the present disclosure is directed to a method for mitigating subsynchronous power oscillations in an inverter-based resource connected to an electric power grid via a series compensation grid connection. The inverter-based resource has a power converter and a generator. The method includes determining one or more rotor current commands for the power converter via a controller. The method also includes applying at least one stator current component to the one or more rotor current commands via a software module of the controller to provide active damping to mitigate subsynchronous power oscillations in the inverter-based resource. In addition, the method includes determining at least one voltage command for the inverter-based resource based on the one or more rotor current commands and at least one stator current component via the controller. In addition, the method includes controlling the inverter-based resource via the controller at least partially based on the voltage command. It should be understood that the method may further include any of the additional features and / or steps described herein.

[0012] In another aspect, the present disclosure is directed to a method for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection. The inverter-based resource has a power converter and a generator. The method includes receiving, via a controller, an indication that the generator is experiencing a negative resistance under a subsynchronous condition. In addition, the method includes compensating for the negative resistance by reducing an effective rotor resistance under the subsynchronous condition, via the controller, wherein reducing the effective rotor resistance is achieved by placing a virtual resistance in parallel with the effective rotor resistance. It should be understood that the method may further include any of the additional features and / or steps described herein.

[0013] In yet another aspect, the present disclosure is directed to a converter controller for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection. The inverter-based resource has a power converter and a generator. The converter controller includes at least one controller having at least one processor. The processor(s) are configured to perform a plurality of operations, including but not limited to determining one or more rotor current commands for the power converter, applying at least one stator current component to the one or more rotor current commands to provide active damping to mitigate subsynchronous power oscillations in the inverter-based resource, determining at least one voltage command for the inverter-based resource based on the one or more rotor current commands and at least one stator current component, and controlling the inverter-based resource based at least in part on the voltage command. It should be understood that the converter controller may further include any of the additional features and / or steps described herein.

[0014] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and together with the description serve to explain the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A complete and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0016] 1 illustrates a single-line diagram of a double-feed wind turbine generator with a structure for converter control for grid tracking applications, according to a conventional configuration;

[0017] Figure 2 illustrates a perspective view of one embodiment of a wind turbine according to the present disclosure;

[0018] Figure 3 illustrated an interior view of a simplified interior view according to one embodiment of the nacelle of the present disclosure;

[0019] Figure 4 A schematic diagram of an embodiment of a wind turbine electric power system suitable for use with the wind turbine shown in FIG. 1 ;

[0020] Figure 5 A schematic diagram of one embodiment of a wind farm with a plurality of wind turbines according to the present disclosure;

[0021] Figure 6 Figures a block diagram of an embodiment of a controller according to the present disclosure;

[0022] Figure 7 Figured a single-line diagram of a double-feed wind turbine generator with converter control for grid formation applications according to the present disclosure;

[0023] Figure 8 Figured a single-line system diagram of a system for providing grid formation control of a double-feed generator of a wind turbine according to the present disclosure;

[0024] Fig. 9 Figured a simplified grid-forming control loop block diagram of a system according to the present disclosure;

[0025] Fig.10 Figures a grid-forming control loop diagram of a system according to the present disclosure, particularly a voltage control loop and a frequency control loop;

[0026] Fig.11 Figured a flowchart of an embodiment of a method for mitigating subsynchronous power oscillation in an inverter-based resource connected to a power grid via a series compensation power grid connection according to the present disclosure;

[0027] Fig.12 illustrating an equivalent circuit diagram of a doubly-fed induction generator for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection in accordance with the present disclosure;

[0028] Fig.13 Figures illustrate an embodiment of the present disclosure for use by placing a parallel resistor R, according to an embodiment of the present disclosure x To compensate for negative R eq (R r ), so that R eq The influence of the system can be reduced and the total resistance of the system (considering the stator and network resistance) becomes positive;

[0029] Fig.14 A schematic diagram of an embodiment of a damping control loop for a grid formation mode based on an inverter resource according to the present disclosure;

[0030] Fig.15A schematic diagram of an embodiment of a damping control loop for a grid formation mode based on an inverter resource according to the present disclosure;

[0031] Fig.16 A schematic diagram of an embodiment of a damping control loop for a grid formation mode of a power converter applied to an inverter-based resource according to the present disclosure;

[0032] Fig.17 A schematic diagram of another embodiment of a damping control loop for a grid formation mode based on an inverter-based resource according to the present disclosure;

[0033] Fig.18 A schematic diagram of another embodiment of a damping control loop for grid formation mode of a power converter applied to an inverter-based resource according to the present disclosure;

[0034] Fig.19 A schematic diagram of an embodiment of a damping control loop for a grid formation mode based on an inverter resource according to the present disclosure;

[0035] Fig. 20 A schematic diagram illustrating an embodiment of a grid tracking mode based on inverter-based resources according to the present disclosure;

[0036] Fig.21 A schematic diagram of an embodiment of a grid tracking mode applied to a power converter based on an inverter-based resource according to the present disclosure;

[0037] Fig. 22 A schematic diagram of an embodiment of a damping control loop for a grid tracking mode based on an inverter-based resource according to the present disclosure;

[0038] Fig.23 Figured a schematic diagram of another embodiment of a damping control loop for grid tracking mode of a power converter applied to an inverter-based resource according to the present disclosure; and

[0039] Fig.24 A flowchart of one embodiment of a method for mitigating subsynchronous power oscillation in an inverter-based resource connected to a power grid via a series compensation power grid connection according to the present disclosure. DETAILED DESCRIPTION

[0040] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explaining the present invention, rather than by way of limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature illustrated or described as part of one embodiment may be used together with another embodiment to produce yet another embodiment. Therefore, it is intended that the present invention covers such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0041] In general, the present disclosure is directed to systems and methods for mitigating subsynchronous power oscillations in inverter-based resources connected to a series compensation network for grid formation and grid tracking. In particular, the negative resistance presented by a DFIG wind turbine under subsynchronous conditions can be compensated by reducing the effective rotor resistance. This is achieved by placing a virtual resistance in parallel with the effective rotor resistance. Grid formation control for wind turbines is designed to have two outer loops, a voltage loop and a frequency loop. However, if the loop bandwidth is kept low, the frequency loop may sometimes fail to mitigate oscillations due to series compensation. Even for higher bandwidth frequency loops, subsynchronous oscillations become prominent when the active power command becomes saturated to its maximum value. While the grid tracking controlled wind turbine does not have any frequency regulation loop, it shows oscillations when the magnitude of the equivalent rotor resistance under subsynchronous conditions exceeds the sum of the stator and network resistances. Therefore, the present disclosure is configured to mitigate oscillations by providing active damping by adding the filtered and amplified stator current to the rotor current command for both the d component and the q component.

[0042] Now referring to the accompanying drawings, Figure 2 A perspective view of one embodiment of a wind turbine 10 according to the present disclosure is illustrated. As shown, the wind turbine 10 generally includes a tower 12 extending from a support surface 14, a nacelle 16 mounted on the tower 12, and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to the hub 20 and extending outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in alternative embodiments, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotating the rotor 18, thereby enabling kinetic energy to be converted from the wind into usable mechanical energy, and subsequently into electrical energy. For example, the hub 20 may be rotatably coupled to a generator 24 ( Figure 3 ), to allow the generation of electrical energy.

[0043] The wind turbine 10 may also include a wind turbine controller 26 centralized within the nacelle 16. However, in other embodiments, the controller 26 may be located within any other component of the wind turbine 10, or at a location external to the wind turbine 10. In addition, the controller 26 may be communicatively coupled to any number of components of the wind turbine 10 in order to control the operation of such components and / or implement corrective or control actions. Thus, the controller 26 may include a computer or other suitable processing unit. Thus, in several embodiments, the controller 26 may include suitable computer-readable instructions that, when implemented, configure the controller 26 to perform a variety of different functions, such as receiving, transmitting and / or executing wind turbine control signals. Thus, the controller 26 may generally be configured to control various operating modes (e.g., startup or shutdown sequences), reduce or increase the ratings of the wind turbine and / or individual components of the wind turbine 10.

[0044] Reference now Figure 2 , a simplified internal view of one embodiment of the nacelle 16 of the wind turbine 10 shown in FIG. 1 is illustrated. As shown, the generator 24 may be disposed within the nacelle 16 and supported on top of the base 46. Typically, the generator 24 may be coupled to the rotor 18 for generating electrical power from the rotational energy generated by the rotor 18. For example, as shown in the illustrated embodiment, the rotor 18 may include a rotor shaft 34 coupled to the hub 20 for rotation therewith. The rotor shaft 34 may, in turn, be rotatably coupled to a generator shaft 36 of the generator 24 through a gearbox 38. As is generally understood, in response to the rotation of the rotor blades 22 and the hub 20, the rotor shaft 34 may provide a low-speed, high-torque input to the gearbox 38. The gearbox 38 may then be configured to convert the low-speed, high-torque input into a high-speed, low-torque output to drive the generator shaft 36, and thus the generator 24.

[0045] The wind turbine 10 may also have one or more pitch drive mechanisms 32 communicatively coupled to the wind turbine controller 26, wherein each pitch adjustment mechanism(s) 32 is configured to rotate a pitch bearing 40, and thus rotate an individual rotor blade(s) 22 about its respective pitch axis 28. Additionally, as shown, the wind turbine 10 may include one or more yaw drive mechanisms 42 configured to change the angle of the nacelle 16 relative to the wind (e.g., by engaging a yaw bearing 44 of the wind turbine 10, which is disposed between the nacelle 16 and the tower 12 of the wind turbine 10).

[0046] In addition, the wind turbine 10 may also include one or more sensors 66, 68 for monitoring various wind conditions of the wind turbine 10. For example, the wind direction 52, wind speed, or any other suitable wind condition near the wind turbine 10 may be measured, such as by using a suitable weather sensor 66. Suitable weather sensors may include, for example, a sound detection and ranging ("SODAR") device, an anemometer, a wind vane, a barometer, or any other sensing device that can provide wind direction information now known in the art or later developed. Still other sensors 68 may be used to measure additional operating parameters of the wind turbine 10, such as voltage, current, vibration, etc., as described herein.

[0047] Reference now Figure 4 , a schematic diagram of one embodiment of a wind turbine power system 100 is illustrated in accordance with aspects of the present disclosure. Although references will be made in this article Figure 4 The system 100 shown in FIG. 1 generally describes the present disclosure, but one of ordinary skill in the art using the disclosure provided herein should understand that aspects of the present disclosure may also be applicable to other power generation systems, and as mentioned above, the present invention is not limited to wind turbine systems.

[0048] exist Figure 4 In the embodiment and as mentioned, the wind turbine 10( Figure 2 ) can be optionally coupled to a gearbox 38, which in turn is coupled to a generator 102, which can be a doubly fed induction generator (DFIG). As shown, the DFIG 102 can be connected to a stator bus 104. In addition, as shown, a power converter 106 can be connected to the DFIG 102 via a rotor bus 108 and to the stator bus 104 via a line-side bus 110. Therefore, the stator bus 104 can provide output multi-phase power (e.g., three-phase power) from the stator of the DFIG 102, and the rotor bus 108 can provide output multi-phase power (e.g., three-phase power) from the rotor of the DFIG 102. The power converter 106 may also include a rotor side converter (RSC) 112 and a line side converter (LSC) 114. The DFIG 102 is coupled to the rotor side converter 112 via the rotor bus 108. Furthermore, the RSC 112 is coupled to the LSC 114 via the DC link 116 , across which is a DC link capacitor 118 . The LSC 114 is in turn coupled to the line side bus 110 .

[0049] The RSC 112 and the LSC 114 may be configured for a normal operating mode in a three-phase pulse width modulation (PWM) arrangement using one or more switching devices such as insulated gate bipolar transistor (IGBT) switching elements. In addition, the power converter 106 may be coupled to a converter controller 120 to control the operation of the rotor side converter 112 and / or the line side converter 114 as described herein. It should be noted that the converter controller 120 may be configured as an interface between the power converter 106 and the turbine controller 26 and may include any number of control devices.

[0050] In a typical configuration, various line contactors and circuit breakers, including, for example, grid breaker 122, may also be included for isolating various components as necessary for normal operation of DFIG 102 during connection to and disconnection from a load, such as power grid 124. For example, system circuit breaker 126 may couple system bus 128 to transformer 130, which may be coupled to power grid 124 via grid breaker 122. In alternative embodiments, fuses may replace some or all of the circuit breakers.

[0051] In operation, the AC power generated at the DFIG 102 by rotating the rotor 18 is provided to the power grid 124 via a dual path defined by the stator bus 104 and the rotor bus 108. On the rotor bus side 108, sinusoidal multi-phase (e.g., three-phase) alternating current (AC) power is provided to the power converter 106. The rotor power side converter 112 converts the AC power provided from the rotor bus 108 into direct current (DC) power, and provides the DC power to the DC link 116. As generally understood, the switching elements (e.g., IGBTs) used in the bridge circuit of the rotor side power converter 112 can be modulated to convert the AC power provided from the rotor bus 108 into DC power suitable for the DC link 116.

[0052] In addition, the line-side converter 114 converts the DC power on the DC link 116 into an AC output power suitable for the power grid 124. In particular, the switching elements (e.g., IGBTs) used in the bridge circuit of the line-side power converter 114 can be modulated to convert the DC power on the DC link 116 into AC power on the line-side bus 110. The AC power from the power converter 106 can be combined with the power from the stator of the DFIG 102 to provide a multi-phase power (e.g., three-phase power) having a frequency that is substantially maintained at the frequency of the power grid 124 (e.g., 50 Hz or 60 Hz).

[0053] In addition, various circuit breakers and switches (such as grid breaker 122, system breaker 126, stator synchronizing switch 132, converter breaker 134, and line contactor 136) may be included in wind turbine power system 100 to connect or disconnect corresponding busbars, such as when excessive current flows and may damage components of wind turbine power system 100 or for other operational considerations. Additional protection components may also be included in wind turbine power system 100.

[0054] In addition, the power converter 106 may receive control signals from, for example, a local control system 176 via the converter controller 120. The control signals may be based, among other things, on a sensed state or operating characteristic of the wind turbine power system 100. Typically, the control signals provide control over the operation of the power converter 106. For example, feedback in the form of a sensed speed of the DFIG 102 may be used to control the conversion of the output power from the rotor bus 108 to maintain a correct and balanced multi-phase (e.g., three-phase) power supply. Other feedback from other sensors may also be used by the (one or more) controllers 120, 26 to control the power converter 106, including, for example, stator and rotor bus voltage and current feedback. Using various forms of feedback information, switch control signals (e.g., gate timing commands for IGBTs), stator synchronization control signals, and circuit breaker signals may be generated.

[0055] Power converter 106 also compensates or adjusts the frequency of the three-phase power from the rotor for variations in, for example, wind speed at hub 20 and rotor blades 22. Thus, the mechanical and electrical rotor frequencies are decoupled, and electrical stator and rotor frequency matching is facilitated substantially independent of mechanical rotor speed.

[0056] In some states, the bidirectional nature of power converter 106, and in particular the bidirectional nature of LSC 114 and RSC 112, facilitates feeding back at least some of the generated electrical power into the generator rotor. More specifically, electrical power may be transmitted from stator bus 104 to line-side bus 110, and then through line contactor 136 and into power converter 106, in particular into LSC 114, which acts as a rectifier and rectifies the sinusoidal three-phase AC power into DC power. The DC power is transmitted into DC link 116. Capacitor 118 facilitates mitigation of DC link voltage amplitude variations by facilitating mitigation of DC ripple that is sometimes associated with three-phase AC rectification.

[0057] The DC power is then transmitted to the RSC 112, which converts the DC electric power into three-phase sinusoidal AC electric power by adjusting the voltage, current and frequency. This conversion is monitored and controlled via the converter controller 120. The converted AC power is transmitted from the RSC 112 to the generator rotor via the rotor bus 108. In this way, generator reactive power control is facilitated by controlling the rotor current and voltage.

[0058] Reference now Figure 5 , the wind turbine power system 100 described herein may be part of a wind farm 50. As shown, the wind farm 50 may include a plurality of wind turbines 52 (including the wind turbine 10 described above) and an overall farm-level controller 56. For example, as shown in the illustrated embodiment, the wind farm 50 includes twelve wind turbines, including the wind turbine 10. However, in other embodiments, the wind farm 50 may include any other number of wind turbines, such as less than twelve wind turbines or more than twelve wind turbines. In one embodiment, the turbine controllers of the plurality of wind turbines 52 are communicatively coupled to the farm-level controller 56, for example, via a wired connection (such as by connecting the turbine controller 26 via a suitable communication link 54 (e.g., a suitable cable). Alternatively, the turbine controllers may be communicatively coupled to the farm-level controller 56 via a wireless connection (such as by using any suitable wireless communication protocol known in the art). In further embodiments, the farm level controller 156 is configured to send and receive control signals to and from the various wind turbines 52 , such as, for example, to distribute real and / or reactive power demands across the wind turbines 52 of the wind farm 50 .

[0059] Reference now Figure 6 , illustrates a block diagram of one embodiment of suitable components that may be included within a controller (such as any of the converter controller 120, turbine controller 26, and / or farm level controller 56 described herein) according to example aspects of the present disclosure. As shown, the controller may include one or more processors 58, computers or other suitable processing units and associated memory device(s) 60 that may include suitable computer-readable instructions that, when implemented, configure the controller to perform a variety of different functions, such as receiving, transmitting, and / or executing wind turbine control signals (e.g., performing the methods, steps, calculations, etc. disclosed herein).

[0060] As used herein, the term "processor" refers not only to what is known in the art as an integrated circuit included in a computer, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Additionally, the memory device(s) 60 may typically include memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk read-only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVD), and / or other suitable memory elements.

[0061] (One or more) such memory devices 160 may generally be configured to store suitable computer-readable instructions that, when implemented by (one or more) processors 58, configure the controller to perform various functions as described herein. Additionally, the controller may also include a communication interface 62 that facilitates communication between the controller and various components of the wind turbine 10. The interface can include one or more circuits, terminals, pins, contacts, conductors, or other components for sending and receiving control signals. In addition, the controller may include a sensor interface 64 (e.g., one or more analog-to-digital converters) that allows signals transmitted from the sensors 66, 68 to be converted into signals that can be understood and processed by (one or more) processors 58.

[0062] Reference now Figure 7-10 , various diagrams of grid formation control for providing a double feed generator for wind turbines according to the present disclosure. In particular, Figure 7 A schematic diagram illustrating one embodiment of a system 200 for providing grid forming control of a doubly-fed generator of a wind turbine according to the present disclosure, and in particular illustrating a single line diagram of a DFIG 102 having a high-level control structure for grid forming features. Figure 8 A single-line system diagram of a system 200 for providing grid formation control of a double-feed generator of a wind turbine according to the present disclosure. Fig. 9 A simplified grid formation control loop block diagram of system 200 according to the present disclosure is illustrated. Fig.10 The grid formation control loop diagram of the system 200 according to the present disclosure is illustrated, in particular the voltage control loop and the frequency control loop.

[0063] Special References Figure 7-9 , the system 200 may include the Figure 41 , where components have the same reference numerals representing similar components. In addition, as shown, the system 200 may include a control structure for controlling a line side converter, and the control structure for controlling the line side converter is similar to the control structure shown in Figure 1. More particularly, as shown, the line side converter control structure may include a DC voltage regulator 212 and a line current regulator 214. Therefore, the DC voltage regulator 212 is configured to generate a line side current command (e.g., ILCmdx) for the line current regulator 214. The line current regulator 214 then generates a line side voltage command (e.g., VLCmdx, VLCmdy) for the modulator 218. The modulator 218 also receives an output from the phase-locked loop 216 (e.g., the phase-locked loop angle θ PLL ) to generate one or more gate pulses for line-side converter 114 . The phase-locked loop 216 typically generates its output using a voltage feedback signal.

[0064] Furthermore, as shown, system 200 may also include a unique control structure for controlling rotor-side converter 112 using grid formation characteristics. In particular, such as Figure 7 As shown in , the system 200 may include a stator voltage regulator 206 for providing such grid forming characteristics. In addition, as shown, the system 200 may include a grid voltage / VAR regulator 202, an inertial power regulator 204, a rotor current regulator 208, and a modulator 210. Therefore, in an embodiment, as shown, the system 200 is configured to determine (one or more) voltage commands (e.g., VS_MAG_Cmd and VS_ANGLE_Cmd) via the voltage / VAR regulator 202 and / or the inertial power regulator 204 using, for example, one or more reference commands from an external controller. In such an embodiment, the external controller may include, for example, the turbine controller 26 of the wind turbine 10 or the farm-level controller 56 of the wind farm 50. In addition, as shown, the (one or more) reference commands may include at least one of a voltage reference (e.g., VT_Ref) or a VAR reference from the farm-level controller 56 and / or a power reference (e.g., Power_Ref) from the turbine controller 26.

[0065] refer to Figure 7, the stator voltage regulator 206 of the system 200 is configured to determine one or more rotor current commands (e.g., IRCmdy and IRCmdx) based on the magnetizing current command 238 and / or the stator current feedback signal 240 of the DFIG 102. Therefore, the output (one or more) from the stator voltage regulator 206 (e.g., rotor current commands IRCmdy, IPCmdx) can be implemented in the rotor current regulator 208 by generating rotor voltage commands (e.g., VRCmdx and VRCmdy) for the modulator 210. The modulator 210 also receives the phase-locked loop angle and the reference angle (e.g., θ) from the phase-locked loop 216. FFBK ) to generate one or more gate pulses for rotor-side converter 112 .

[0066] Special References Fig. 9 and Fig.10 And as mentioned, the grid formation control scheme 250 includes a voltage-frequency control strategy that is used to operate the DFIG 102 in a grid formation mode (GFM), where v* and f* are instantaneous voltage and frequency references along the PCC space vector direction, Qs* and Qs are reference reactive power and feedback reactive power, ΔQ and ΔP are outputs of the voltage and frequency regulation loops, Ps* is the active power command, Pmax and Pmin are the maximum and minimum limits of the active power command, T* em is the torque command, i rd *、i rd is the d component of the rotor current command and feedback, i rq *、i rd is the d component of the rotor current command and feedback, ψs is the stator flux, ωr is the rotor angular frequency, and v rd *、v rq * are the d and q components of the rotor voltage command.

[0067] As shown, GFM control 250 is based on a reference system derived from an instantaneous point of common coupling (PCC) dynamics. An instantaneous reference space vector is established along the direction of the PCC space vector. Thus, the deviation of the PCC space vector (in terms of magnitude and angular velocity) relative to the reference space vector is controlled via the GFM loop. For example, as shown, the voltage control loop 252 generates the d component (v rd *) 256, and the frequency control loop 254 generates a q component of the rotor voltage (v rq *)258. More specifically, the voltage control loop 252 is based on v sqand v* generate an incremental reactive power value ΔQ 260. Similarly, the frequency control loop 254 generates an incremental active power value ΔP 262 based on fs and f*. Thus, as shown, the voltage control loop 252 generates a reactive power reference Q based on Qs* 264 and the incremental reactive power value ΔQ 260. ref 265. Similarly, the frequency control loop 254 generates an active power reference P based on Ps*266 and incremental active power value ΔP 262. ref 267. Therefore, the voltage and frequency control loops 252, 254 are each configured to generate the d component and the q component (i) of the rotor current commands 268, 270 rd *、i rq *). Thus, as shown, the d component and q component of the rotor current commands 268, 270 (i) rd *、i rq *) Then, it is used to generate the d component of the rotor voltage (v rd *)256 and the q component of the rotor voltage (v rq *)258.

[0068] Series capacitors are often installed in long distance AC transmission lines to increase the power transfer capability of the line. The series capacitor creates a resonant circuit that may interact with the converter control of the power electronics. Figure 7 Doubly-fed wind turbines such as those illustrated in FIG. 5 may be susceptible to this type of interaction. Without proper damping, the oscillations may be unstable and cause the wind farm 50 to trip. Thus, the systems and methods of the present disclosure are directed to mitigating subsynchronous power oscillations in inverter-based resources connected to the power grid via a series compensation grid connection, such as Figure 7-9 The structure / schematic diagram shown in .

[0069] In particular and now with reference to Fig.11 , a flow chart of one embodiment of a method 300 for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection is provided. The inverter-based resource as described herein may include, for example, a wind turbine power system, a solar power system, an energy storage power system, or a combination thereof. Generally, reference is made herein to Figure 2-10 The wind turbine 10 describes the method 300 . However, it will be appreciated that the disclosed method 300 can be implemented with a wind turbine with any other suitable configuration. In addition, although Fig.11The steps performed in a particular order are depicted for purposes of illustration and discussion, but the methods discussed herein are not limited to any particular order or arrangement. Using the disclosure provided herein, those skilled in the art will appreciate that the various steps of the methods disclosed herein may be omitted, rearranged, combined, and / or adjusted in various ways without departing from the scope of the present disclosure.

[0070] As shown at (302), method 300 includes determining, via a controller, one or more rotor current commands for a power converter. In such embodiments, the controller may be a turbine controller, a converter controller, or any other suitable controller as part of an inverter-based resource or separate from an inverter-based resource.

[0071] As shown at (304), the method 300 includes applying at least one stator current component to (one or more) rotor current commands via a software module of the controller to provide active damping to mitigate subsynchronous power oscillations in the inverter-based resource. In an embodiment, for example, applying the (one or more) stator current components to the (one or more) rotor current commands may include applying a d-component stator current component and a q-component stator current component to the d component and q-component of the (one or more) rotor current commands, respectively. In such an embodiment, the (one or more) stator current components may include a d-component stator current component and a q-component stator current component. In an alternative embodiment, applying the (one or more) stator current components to the (one or more) rotor current commands may include applying only the q-component stator current component to the q-component of the (one or more) rotor current commands. In such an embodiment, the (one or more) stator current components may include a q-component stator current component.

[0072] In a further embodiment, the method 300 may include filtering and amplifying the d-component stator current component and the q-component stator current component before applying the d-component stator current component and the q-component stator current component to the d-component and the q-component of the one or more rotor current commands, respectively. In another embodiment, the method 300 may include filtering and amplifying the q-component stator current component before applying the q-component stator current component to the q-component of the (one or more) rotor current commands.

[0073] Still reference Fig.11 As shown at (306), the method 300 includes determining, via a controller, at least one voltage command for the inverter-based resource based on the one or more rotor current commands and the at least one stator current component. As shown at (308), the method 300 includes controlling, via the controller, the inverter-based resource based at least in part on the voltage command.

[0074] In certain embodiments, method 300 may include controlling inverter-based resources using grid forming control. In such embodiments, determining rotor current command(s) for the power converter may include determining rotor current command(s) based on a magnetizing current command and / or a stator current feedback signal of the generator.

[0075] refer to Figure 12-19 Better understanding Fig.11 Method 300. Special references Fig.12 , a schematic diagram 400 illustrating the proposed method for mitigating subsynchronous power oscillations in inverter-based resources connected to a power grid via a series compensation grid connection. More specifically, a grid voltage frequency ω is provided. s Analysis in the synchronous synchronous reference system. In addition, equations (1) and (2) provide Fig.12 The relationship between voltage and current illustrated in this can be used to calculate the d component of the rotor voltage (v rd *)256 and the q component of the rotor voltage (v rq *)258, as described herein.

[0076] Where Rr is the rotor resistance referred to the stator, ωr is the rotor angular frequency, σLr is the transient inductance of the rotor, where σ is the leakage coefficient of the machine, Lm is the magnetizing inductance, Ls is the stator inductance, Lr is the rotor inductance, and ψds is the stator flux.

[0077] In particular, the equivalent rotor resistor R at the subsynchronous frequency eq becomes negative, which can inject negative damping into the system, leading to oscillations. This is mainly due to the high bandwidth rotor current control loop that adds effective rotor side resistance. Therefore, to prevent oscillations, damping needs to be positive. Therefore, compensation for negative resistance is required. Therefore, if Fig.13 As shown in eq (R r ) is by placing a parallel resistor R x , so that R eq The influence of the system can be reduced and the total resistance of the system (considering the stator and network resistance) becomes positive, i.e. positive damping. This relationship is also represented by the following equation (3).

[0078] Reference now Figure 14-16 , schematic diagram of an embodiment of the damping control loop 500 according to the present disclosure, wherein R is r is the rotor resistance related to the stator, ω r is the rotor angular frequency, σLr is the transient inductance of the rotor, where σ is the leakage coefficient of the machine, L m is the magnetizing inductance, L s is the stator inductance, L r is the rotor inductance, and ψ ds is the stator flux, k p and k i is the proportional and integral gain of the rotor current regulator loop, k 1s is the gain of the filtered stator current loop.

[0079] In particular, as shown, the damping control can be achieved by filtering and amplifying the stator current (i.e., i.e. ds and i qs ) and (one or more) rotor current commands (i.e., i dr * and i qr *) are added to provide. Considering i qr * and i dr *With internal current loop and small k i Compared with slow dynamics, the voltage across the leakage rotor inductor can be expressed by the following equations (4) and (5):

[0080] The d and q components of the rotor current can be expressed by the following equations (6) and (7) according to the stator current:

[0081] Therefore, equations (6) and (7) can be modified using the following equations (8) and (9), where the dotted circle portion represents the effective rotor resistance:

[0082] Taking into account the proportional gain kp, the effective rotor resistor can be found using the following equation (10): R′ r =k p +R r Equation (10)

[0083] Therefore, in such an embodiment, in order to place the parallel resistor R x , use the following equation (11) to calculate the value of ks1:

[0084] Therefore, reference Figure 14-16 , provides a method similar to Fig. 9 and 10The grid formation mode of the grid formation mode (GFM) operates the grid formation control scheme 550 of the voltage-frequency control strategy of the DFIG 102 . Furthermore, as shown, the grid formation control scheme 550 may include Fig. 9 and 10 272, 274, wherein the same components have similar reference numerals. However, as shown, the grid forming control scheme 550 further includes the filtered and amplified d and q components (i.e., i ds and i qs ) and (one or more) rotor current commands (i.e., i dr * and i qr *) add, this is Fig. 9 and 10 does not exist in it. Thus, the filtered and amplified d and q components of the stator currents 272, 274 provide damping control as described herein. In particular, such as Fig.14 and 15 As shown in , the filtered and amplified d and q components of the stator currents 272 , 274 may be filtered via high pass filters 276 , 278 or any other suitable filter followed by respective amplifiers 280 , 282 .

[0085] Reference now Figure 17-19 , schematic diagram of another embodiment of the damping control loop 600 according to the present disclosure, wherein v*, f* are instantaneous voltage and frequency references along the PCC spatial vector direction, Q ref , Q s is the reference and feedback reactive power, P ref is the active power command, T* em is the torque command, kp and ki are the proportional and integral gains of the rotor current regulator loop, ks is the gain of the filtered q component of the stator current loop, Rr is the rotor resistance involved in the stator, ωr is the rotor angular frequency, σLr is the transient inductance of the rotor, σ is the leakage coefficient of the machine, L m is the magnetizing inductance, L s is the stator inductance, L r is the rotor inductance, and ψ ds is the stator flux.

[0086] In particular, as shown, the damping control can be performed by filtering and amplifying the stator current (ie, i.e. qs ) and (one or more) q component rotor current command (i.e., i qr *) are added to provide. Considering i qr *With internal current loop and small k iCompared with slow dynamics, the voltage across the leakage rotor inductor can be represented by the following equations (12), (13) and (14), where R in equation (14) is r +k p -k p k s1 (L m / L s ) represents the q component of the effective rotor resistance:

[0087] The reduction of rotor equivalent resistance is achieved by introducing k s *i qs To place the value R x The parallel resistance, k s The value of , can be selected from equation (14). Furthermore, in such embodiments, a high pass filter (HPF) may be used to filter the steady-state component of the stator current.

[0088] Therefore, reference Figure 17-19 , provides a method similar to Figure 9-10 and 14-16 of the grid formation mode (GFM) grid formation mode operation DFIG 102 voltage-frequency control strategy of the grid formation control scheme 650. In addition, as shown, the grid formation control scheme 650 may include Figure 9-10 14-16, where the same components have similar reference numerals. However, as shown, the grid forming control scheme 650 only includes the filtered and amplified q component (i.e., i qs ) and the q-component rotor current command (i.e., i qr *) addition, which is different from Figure 9-10 and 14-16 embodiments. Thus, the filtering and amplified q component of the stator current 274 provides damping control as described herein. In particular, such as Fig.17 and 19 As shown in this, the filtered and amplified q component of the stator current 274 may be filtered via high pass filter 278 or any other suitable filter and amplified via amplifier 282 .

[0089] In alternative embodiments, the systems and methods described herein may include using grid tracking control to control inverter-based resources. In particular, Fig. 20 Figure 750 of the grid tracking control loop diagram 750 based on the inverter-based resource according to the present disclosure, and Fig.21 The grid tracking control loop diagram 750 for inverter-based resources applied to power converter 106 according to the present disclosure. Therefore, Figure 20-21In the figure, a schematic diagram of a traditional grid tracking control 750 based on the resource of the inverter is illustrated, wherein Q ref , Q s is the reference and feedback reactive power, P ref is the active power command, T* em is the torque command, i rd *、i rd is the d component of the rotor current command and feedback, i rq *、i rq is the q component of the rotor current command and feedback, ψs is the stator flux, ωr is the rotor angular frequency, and v rd *、v rq * is the d and q components of the rotor voltage command. In particular, as shown, the grid tracking mode receives reactive power and active power references (Q ref , P ref ) and adjust the reactive and active power references via various proportional integral regulators (PIs) to obtain the d component and q component of the rotor voltages 256, 258 (v rd *、v rq *).

[0090] Therefore, if Fig. 22 and 23 As shown in , a schematic diagram of another embodiment of a damping control loop 700 according to the present disclosure is illustrated, and the damping control loop 700 can be applied to a grid tracking control scheme, such as a grid tracking control 750. In particular, Fig. 22 and 23 800 is a diagram of a grid tracking control loop with a damping control 850 according to the present disclosure. In particular, as shown, the damping control 850 can be implemented by converting the filtered and amplified d and q components (i.e., i ds and i qs ) and (one or more) rotor current commands (i.e., i dr * and i qr *) are added to provide, which in Fig. 9 and 10 does not exist in it. Thus, the filtering and amplified d and q components of the stator currents 272, 274 provide damping control as described herein. In particular, such as Fig. 22 As shown in , the filtered and amplified d and q components of the stator currents 272 , 274 may be filtered via high pass filters 276 , 278 or any other suitable filter followed by respective amplifiers 280 , 282 .

[0091] Reference now Fig.24, a flow chart of one embodiment of a method 900 for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection is provided. Figure 2-10 The wind turbine 10 describes the method 900. However, it will be appreciated that the disclosed method 800 can be implemented with a wind turbine with any other suitable configuration. Also, although Fig.24 The steps performed in a particular order are depicted for purposes of illustration and discussion, but the methods discussed herein are not limited to any particular order or arrangement. Using the disclosure provided herein, those skilled in the art will appreciate that the various steps of the methods disclosed herein may be omitted, rearranged, combined, and / or adjusted in various ways without departing from the scope of the present disclosure.

[0092] As indicated at (902), the method 900 includes receiving, via a controller, an indication that the generator is experiencing a negative resistance under a subsynchronous condition. As indicated at (904), the method 900 includes compensating, via the controller, for the negative resistance under the subsynchronous condition by reducing an effective rotor resistance, wherein reducing the effective rotor resistance is accomplished by placing a virtual resistance in parallel with the effective rotor resistance.

[0093] Further aspects of the invention are provided by the subject matter of the following clauses: Clause 1. A method for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection, the inverter-based resource having a power converter and a generator, the method comprising: Determine one or more rotor current commands for the power converter via the controller; applying, via a software module of the controller, at least one stator current component to the one or more rotor current commands to provide active damping to mitigate the subsynchronous power oscillations in the inverter-based resource; determines at least one voltage command for the inverter-based resource via the controller based on the one or more rotor current commands and the at least one stator current component; and The inverter-based resource is controlled via the controller based at least in part on the voltage command. Clause 2. The method of Clause 1, wherein applying the at least one stator current component to the one or more rotor current command further comprises: A d-component stator current component and a q-component stator current component are applied to the d-component and q-component of the one or more rotor current commands, respectively, and the at least one stator current component includes the d-component stator current component and the q-component stator current component. Clause 3. The method according to clause 2 further includes filtering and amplifying the d-component stator current component and the q-component stator current component before applying the d-component stator current component and the q-component stator current component to the d-component and the q-component of the one or more rotor current commands, respectively. Clause 4. The method as claimed in any of the preceding clauses, wherein applying the at least one stator current component to the one or more rotor current command further comprises: The q component stator current component is applied to the q component of the one or more rotor current commands, the at least one stator current component including the q component stator current component. Clause 5. The method of clause 4, further comprising filtering and amplifying the q-component stator current component before applying the q-component stator current component to the q-component of the one or more rotor current commands. Article 6. The method as set forth in any of the preceding clauses further comprises controlling the inverter-based resources using grid formation control. Clause 7. The method of Clause 6, wherein determining the one or more rotor current command for the power converter further comprises: The one or more rotor current commands are determined based on one or more power signals, wherein the one or more power signals are determined based on at least one of one or more frequency or voltage signals. Article 8. The method as set forth in any of the preceding clauses further comprises controlling the inverter-based resources using grid tracking control. Clause 9. The method of any of the preceding clauses, wherein the inverter-based resource comprises at least one of a wind turbine power system, a solar power system, an energy storage power system, or a combination thereof. Clause 10. The method of Clause 9, wherein the controller comprises at least one of a turbine controller or a converter controller of the wind turbine power system. Clause 11. A method for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection, the inverter-based resource having a power converter and a generator, the method comprising: Receive via the controller that the generator is experiencing a negative resistance under subsynchronization conditions; The negative resistance is compensated by reducing an effective rotor resistance via the controller under the subsynchronous condition, wherein reducing the effective rotor resistance is achieved by placing a dummy resistance in parallel with the effective rotor resistance. Clause 12. A converter controller for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection, the inverter-based resource having a power converter and a generator, the converter controller comprising: At least one controller, which includes at least one processor, the at least one processor configured to perform a plurality of operations, the plurality of operations including: Determine one or more rotor current commands for the power converter; Apply at least one stator current component to the one or more rotor current commands to provide active damping to alleviate the subsynchronous power oscillation in the inverter-based resource; determining at least one voltage command for the inverter-based resource based on the one or more rotor current commands and the at least one stator current component; and controlling the inverter-based resource based at least in part on the voltage command. Clause 13. The converter controller of Clause 12, wherein applying the at least one stator current component to the one or more rotor current command further comprises: A d-component stator current component and a q-component stator current component are applied to the d-component and q-component of the one or more rotor current commands, respectively, and the at least one stator current component includes the d-component stator current component and the q-component stator current component. Clause 14. The converter controller of Clause 13, wherein the plurality of operations further comprises: The d-component stator current component and the q-component stator current component are filtered and amplified before being applied to the d-component and the q-component of the one or more rotor current commands, respectively. Clause 15. The converter controller of clause 12-14, wherein applying the at least one stator current component to the one or more rotor current command further comprises: The q component stator current component is applied to the q component of the one or more rotor current commands, the at least one stator current component including the q component stator current component. Clause 16. The converter controller of Clause 15, wherein the plurality of operations further comprises: The q component stator current component is filtered and amplified before applying the q component to the q component of the one or more rotor current commands. Clause 17. The converter controller of clause 12-16, wherein the plurality of operations further comprises controlling the inverter-based resources using grid formation control. Clause 18. The converter controller of Clause 17, wherein determining the one or more rotor current commands for the power converter further comprises: The one or more rotor current commands are determined based on one or more power signals, wherein the one or more power signals are determined based on at least one of one or more frequency or voltage signals. Clause 19. The converter controller of clause 12-18, wherein the plurality of operations further comprises controlling the inverter-based resources using grid tracking control. Clause 20. A converter controller as described in clauses 12-19, wherein the inverter-based resource includes at least one of a wind turbine power system, a solar power system, an energy storage power system, or a combination thereof, and wherein the controller includes at least one of a turbine controller or a converter controller.

[0094] This written description uses examples, including the best mode, to disclose the invention, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems, and performing any combined methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are expected to fall within the scope of the claims if they have structural elements that are identical to the literal language of the claims, or if they include equivalent structural elements that have insubstantial differences from the literal language of the claims.

Claims

1. A method for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection, the inverter-based resource having a power converter and a generator, the method comprising: determining, via a controller, one or more rotor current commands for the power converter; applying, via a software module of the controller, at least one stator current component to the one or more rotor current commands to provide active damping to mitigate the subsynchronous power oscillations in the inverter-based resource; determining, via the controller, at least one voltage command for the inverter-based resource based on the one or more rotor current commands and the at least one stator current component; as well as The inverter-based resource is controlled via the controller based at least in part on the voltage command.

2. The method according to claim 1, wherein: Applying the at least one stator current component to the one or more rotor current commands further comprises: A d-component stator current component and a q-component stator current component are applied to the d-component and q-component of the one or more rotor current commands, respectively, and the at least one stator current component includes the d-component stator current component and the q-component stator current component.

3. The method of claim 2, further comprising filtering and amplifying the d-component stator current component and the q-component stator current component before applying the d-component stator current component and the q-component stator current component to the d-component and the q-component of the one or more rotor current commands, respectively.

4. The method according to claim 1, wherein: Applying the at least one stator current component to the one or more rotor current commands further comprises: A q-component stator current component is applied to the q-component of the one or more rotor current commands, the at least one stator current component including the q-component stator current component. 5 . The method of claim 4 , further comprising filtering and amplifying the q-component stator current component before applying the q-component stator current component to the q-component of the one or more rotor current commands. 6 . The method of claim 1 , further comprising controlling the inverter-based resource using grid forming control.

7. The method according to claim 6, wherein: Determining the one or more rotor current commands for the power converter further comprises: The one or more rotor current commands are determined based on one or more power signals, wherein the one or more power signals are determined based on at least one of one or more frequency or voltage signals. 8 . The method of claim 1 , further comprising controlling the inverter-based resource using grid tracking control.

9. The method according to claim 1, wherein: The inverter-based resource includes at least one of a wind turbine power system, a solar power system, an energy storage power system, or a combination thereof.

10. The method according to claim 9, wherein: The controller includes at least one of a turbine controller or a converter controller of the wind turbine power system.

11. A method for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection, the inverter-based resource having a power converter and a generator, the method comprising: receiving, via a controller, an indication that the generator is experiencing negative resistance in a subsynchronous condition; The negative resistance is compensated by reducing an effective rotor resistance via the controller under the subsynchronous condition, wherein reducing the effective rotor resistance is achieved by placing a virtual resistance in parallel with the effective rotor resistance.

12. A converter controller for mitigating subsynchronous power oscillations in an inverter-based resource connected to a power grid via a series compensation grid connection, the inverter-based resource having a power converter and a generator, the converter controller comprising: At least one controller comprising at least one processor configured to perform a plurality of operations comprising: determining one or more rotor current commands for the power converter; applying at least one stator current component to the one or more rotor current commands to provide active damping to mitigate the subsynchronous power oscillations in the inverter-based resource; determining at least one voltage command for the inverter-based resource based on the one or more rotor current commands and the at least one stator current component; and The inverter-based resource is controlled based at least in part on the voltage command.

13. The converter controller according to claim 12, wherein: Applying the at least one stator current component to the one or more rotor current commands further comprises: A d-component stator current component and a q-component stator current component are applied to the d-component and q-component of the one or more rotor current commands, respectively, and the at least one stator current component includes the d-component stator current component and the q-component stator current component.

14. The converter controller according to claim 13, wherein: The plurality of operations further include: The d-component stator current component and the q-component stator current component are filtered and amplified before being applied to the d-component and the q-component of the one or more rotor current commands, respectively.

15. The converter controller according to claim 12, wherein: Applying the at least one stator current component to the one or more rotor current commands further comprises: A q-component stator current component is applied to the q-component of the one or more rotor current commands, the at least one stator current component including the q-component stator current component.

16. The converter controller according to claim 15, wherein: The plurality of operations further include: The q-component stator current component is filtered and amplified before being applied to the q-component of the one or more rotor current commands.

17. The converter controller according to claim 12, wherein: The plurality of operations further include controlling the inverter-based resource using grid forming control.

18. The converter controller according to claim 17, wherein: Determining the one or more rotor current commands for the power converter further comprises: The one or more rotor current commands are determined based on one or more power signals, wherein the one or more power signals are determined based on at least one of one or more frequency or voltage signals.

19. The converter controller of claim 12, wherein: The plurality of operations further include controlling the inverter-based resource using grid tracking control.

20. The converter controller of claim 12, wherein: The inverter-based resource comprises at least one of a wind turbine power system, a solar power system, an energy storage power system, or a combination thereof, and wherein the controller comprises at least one of a turbine controller or a converter controller.

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