System and method for controlling reactive power from a reactive power compensation device

Abstract

The present invention relates to systems and methods for controlling reactive power from a reactive power compensation device, and in particular a method for operating a power generation system that provides active and reactive power to a power grid includes receiving a reactive power demand made to the power generation system in operating conditions of the power generation system and the power grid. Further, the method includes separating reactive power control and voltage control between a generator and the reactive power compensation device in order to reduce an oscillatory response of the reactive power output from the reactive power compensation device and the generator. Further, the method includes operating the reactive power compensation device in a reactive power control mode via a device controller to generate at least a portion of the reactive power demand.

Description

Technical Field

[0001] This disclosure generally relates to power generation systems, and more particularly to systems and methods for controlling reactive power from reactive power compensation devices in a wind turbine system in order to reduce the oscillating response of reactive power output from both the reactive power compensation devices and the generator stator. Background Technology

[0002] Typically, during wind turbine operation, wind impacts the rotor blades, and the blades convert wind energy into mechanical rotational torque that drives a low-speed shaft. The low-speed shaft drives a gearbox, which then increases the low rotational speed of the low-speed shaft to drive a high-speed shaft at an increased rotational speed, whereby the high-speed shaft rotatably drives the generator rotor. In many conventional wind turbine configurations, the generator is electrically coupled to a bidirectional power converter, which includes a rotor-side converter (RSC) coupled to a line-side converter (LSC) via a regulated DC link. Each of the RSC and LSC typically includes a set of pulse-width modulated switching devices, such as insulated-gate bipolar transistors (IGBT modules). The LSC converts the DC power on the DC link to AC output power, which is combined with power from the generator stator to provide multiphase power at a frequency substantially maintained at the grid bus frequency (e.g., 50 Hz or 60 Hz).

[0003] The aforementioned system is commonly referred to as a doubly-fed induction generator (DFIG) system. Its operation involves rotor windings connected to the grid via slip rings and a power converter controlling the rotor current and voltage. Controlling the rotor voltage and current allows the generator to maintain synchronization with the grid frequency even as wind turbine speeds change (e.g., the rotor frequency may differ from the grid frequency). Furthermore, the primary source of reactive power from the DFIG system is from the RSC via the generator (rotor-side reactive power) and LSC (line-side reactive power). Using a power converter (specifically the RSC) to control the rotor current / voltage makes it possible to regulate the reactive power (and active power) fed to the grid from the RSC independently of the generator's rotational speed. Additionally, the generator can import or export reactive power, allowing the system to support the grid during periods of severe voltage fluctuations.

[0004] Typically, the amount of reactive power supplied from the wind farm to the grid under steady-state and transient conditions is established through code requirements specified by the grid operator, whereby the wind farm controller determines the reactive power demand for each wind turbine within the wind farm. A local controller at each wind turbine receives and distributes the reactive power demand among generator sources (e.g., between generator-side reactive power and line-side reactive power).

[0005] It is known to increase the reactive power capacity of wind farms by using reactive power compensation devices such as Static VAR Compensators (SVCs) or Static VAR Generators (SVGs) on one or more common collector buses shared by wind turbines. For example, U.S. Patent Application Publication No. 2017 / 0025858 describes a wind power plant connected to a power grid, comprising multiple wind turbine generators and a Static Synchronous Compensator (STATCOM) device on a common bus shared with the wind turbine generators. In a first control mode, the wind turbine generators and the STATCOM operate in a master-slave relationship for reactive power generation. A second control mode is implemented based on a trigger signal such as a low-voltage event on the grid, in which the wind turbine generators and the STATCOM are switched to a slave-master relationship for reactive power generation.

[0006] There is a need in industry for an improved system and approach that integrates local auxiliary reactive power sources with wind turbines and coordinates the generation of reactive power from different local sources at the wind turbine level. Summary of the Invention

[0007] Aspects and advantages of the invention will be set forth in part in the description which follows, or may be apparent from the description, or may be learned by practice of the invention.

[0008] In one aspect, this disclosure relates to a method for operating a power generation system that supplies active and reactive power to a power grid. The power generation system includes a generator coupled to a power conversion component and a dedicated reactive power compensation device. Furthermore, the power conversion component and the reactive power compensation device each include a converter controller and a device controller. The method includes receiving reactive power demands made by the power generation system under operating conditions of the power generation system and under grid conditions. Furthermore, the method includes separating reactive power control and voltage control between the generator and the reactive power compensation device to reduce oscillating responses of reactive power output from the reactive power compensation device and the generator. Additionally, the method includes operating the reactive power compensation device in a reactive power control mode via the device controller to generate at least a portion of the reactive power demand.

[0009] In one embodiment, the method may include operating the generator in voltage control mode via a converter controller to control the generator's terminal voltage. In such an embodiment, the reactive power control mode of the reactive power compensation device does not interfere with the generator's voltage control mode at the point of common coupling of the power generation system.

[0010] In one embodiment, operating the reactive power compensation device in reactive power control mode may include: determining the maximum reactive power capacity of each of the power conversion component, the generator, and the reactive power compensation device; and coordinating the supply of reactive power demand from the generator and the reactive power compensation device by prioritizing the reactive power compensation device as a first reactive power source and prioritizing the generator and / or the power conversion component as a second reactive power source.

[0011] In another embodiment, during the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation device, all reactive power demand can be supplied by the reactive power compensation device. Alternatively, during the coordination step, when the reactive power demand is greater than the maximum reactive power capacity of the reactive power compensation device, the maximum reactive power capacity of the reactive power compensation device can be supplied, and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation device can be allocated to the generator and / or power conversion components.

[0012] In another embodiment, the maximum reactive power capacity of the generator, power conversion components, and reactive power compensation equipment may be determined based on any one or a combination of the power system operating conditions, ambient temperature, or thermal constraints of the generator, rating limits of the power conversion components, or rating limits of the reactive power compensation equipment.

[0013] In an additional embodiment, the maximum reactive power capacity of the generator, power conversion components, and reactive power compensation equipment can be determined continuously or periodically.

[0014] In several embodiments, the power generation system may include wind turbines, and the generator may include a doubly-fed induction generator (DFIG). In a particular embodiment, the wind turbine may be one of multiple wind turbines within a wind farm that supplies active and reactive power to the grid. In such an embodiment, reactive power demand may be determined by a wind farm-level controller within the wind farm and transmitted to a local controller at the wind turbine.

[0015] In another aspect, this disclosure relates to a wind turbine system configured to supply active and reactive power to a power grid. The wind turbine system includes a wind turbine comprising a rotor, a hub, and a plurality of rotor blades coupled to the hub. The wind turbine system also includes a doubly-fed induction generator (DFIG) system coupled to the rotor. The DFIG system includes a generator coupled to power conversion components having a line-side converter (LSC) and a rotor-side converter (RSC), a reactive power compensation device operatively configured with the DFIG system to generate reactive power, and a converter controller. The reactive power compensation device further includes an equipment controller. Furthermore, the equipment controller is configured to: receive reactive power demands made by the wind turbine system under operating conditions and grid conditions; and to decouple reactive power control and voltage control between the generator and the reactive power compensation device to reduce the oscillating response of reactive power output from the reactive power compensation device and the generator.

[0016] In another aspect, this disclosure relates to a method for operating a power generation system that supplies active and reactive power to a power grid. The power generation system includes a generator connected to a power conversion component and a dedicated reactive power compensation device. The method includes receiving reactive power demands made by the power generation system under operating conditions and grid conditions. Furthermore, the method includes independently controlling the reactive power of the power generation system and the terminal voltage of the generator via separate controllers of the reactive power compensation device and the power conversion component, respectively, to reduce the oscillating response of the reactive power output from the reactive power compensation device and the generator.

[0017] Technical Solution 1. A method for operating a power generation system that supplies active and reactive power to a power grid, the power generation system comprising a generator connected to a power conversion component and a dedicated reactive power compensation device, the power conversion component and the reactive power compensation device respectively comprising a converter controller and a device controller, the method comprising:

[0018] Receive reactive power demands from the power generation system under the operating state and grid state of the power generation system;

[0019] Separating reactive power control and voltage control between the generator and the reactive power compensation device is intended to reduce the oscillating response of reactive power output from both the reactive power compensation device and the generator; and

[0020] The reactive power compensation device is operated in reactive power control mode via the device controller to generate at least a portion of the reactive power demand.

[0021] Technical Solution 2. The method according to Technical Solution 1, characterized in that it further includes: operating the generator in voltage control mode via the converter controller to control the terminal voltage of the generator, wherein the reactive power control mode of the reactive power compensation device does not interfere with the voltage control mode of the generator at the common coupling point of the power generation system.

[0022] Technical Solution 3. The method according to Technical Solution 2, characterized in that operating the reactive power compensation device in the reactive power control mode further includes:

[0023] Determine the maximum reactive power capacity of each of the power conversion component, the generator, and the reactive power compensation device; and

[0024] The supply of reactive power demand from the power conversion component, the generator, and / or the reactive power compensation device is coordinated by prioritizing the reactive power compensation device as a first reactive power source and prioritizing the generator and / or the power conversion component as a second reactive power source.

[0025] Technical Solution 4. The method according to Technical Solution 3, characterized in that, in the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation device, all the reactive power demand is supplied by the reactive power compensation device.

[0026] Technical Solution 5. The method according to Technical Solution 3, characterized in that, in the coordination step, when the reactive power demand is greater than the maximum reactive power capacity of the reactive power compensation device, the maximum reactive power capacity of the reactive power compensation device is supplied, and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation device is allocated to the generator and / or the power conversion component.

[0027] Technical Solution 6. The method according to Technical Solution 3, wherein the maximum reactive power capacity of the power conversion component, the generator and / or the reactive power compensation device is determined based on any one or a combination of the power system operating state, ambient temperature or thermal constraints of the generator, rated value limits of the power conversion component or rated value limits of the reactive power compensation device.

[0028] Technical Solution 7. The method according to Technical Solution 3, characterized in that the maximum reactive power capacity of the power conversion component, the generator and / or the reactive power compensation device is continuously or periodically determined.

[0029] Technical Solution 8. The method according to Technical Solution 1, characterized in that the power generation system includes a wind turbine, and the generator includes a doubly fed induction generator (DFIG).

[0030] Technical Solution 9. The method according to Technical Solution 8, characterized in that the wind turbine is one of a plurality of wind turbines in a wind farm that supplies active power and reactive power to the power grid, and wherein the reactive power demand is determined by a wind farm-level controller in the wind farm and transmitted to a local controller at the wind turbine.

[0031] Technical Solution 10. A wind turbine system configured to supply active and reactive power to the power grid, the wind turbine system comprising:

[0032] A wind turbine, comprising a rotor, a hub, and a plurality of rotor blades connected to the hub;

[0033] A doubly fed induction generator (DFIG) system coupled to the rotor, the DFIG system comprising a generator coupled to power conversion components having a line-side converter (LSC), a rotor-side converter (RSC), and a converter controller;

[0034] A reactive power compensation device, operably configured with the DFIG system to generate reactive power, the reactive power compensation device including a device controller configured to:

[0035] Receive reactive power demands from the wind turbine system under its operating state and grid conditions; and

[0036] The reactive power control and voltage control between the generator and the reactive power compensation device are separated in order to reduce the oscillating response of the reactive power output from the reactive power compensation device and the generator.

[0037] Technical Solution 11. The wind turbine system according to Technical Solution 10, characterized in that the equipment controller is further configured to: operate the reactive power compensation device in a reactive power control mode to generate at least a portion of the reactive power demand.

[0038] Technical Solution 12. The wind turbine system according to Technical Solution 11, characterized in that the converter controller is configured to operate the generator in the voltage control mode in order to control the terminal voltage of the generator, wherein the reactive power control mode of the reactive power compensation device does not interfere with the voltage control mode of the generator at the common coupling point of the power generation system.

[0039] Technical Solution 13. The wind turbine system according to Technical Solution 11, characterized in that the equipment controller is further configured to:

[0040] Determine the maximum reactive power capacity of each of the power conversion component, the generator, and the reactive power compensation device; and

[0041] The supply of reactive power demand from the power conversion component, the generator, and / or the reactive power compensation device is coordinated by prioritizing the reactive power compensation device as a first reactive power source and prioritizing the generator and / or the power conversion component as a second reactive power source.

[0042] Technical Solution 14. The wind turbine system according to Technical Solution 13, characterized in that the maximum reactive power capacity of the power conversion component, the generator and / or the reactive power compensation device is determined based on any one or a combination of the power system operating state, ambient temperature or the thermal constraint of the generator, the rated value limit of the power conversion component or the rated value limit of the reactive power compensation device.

[0043] Technical Solution 15. The wind turbine system according to Technical Solution 10, characterized in that the wind turbine is one of a plurality of wind turbines in a wind farm that supplies active power and reactive power to the power grid, and wherein the reactive power demand is determined by a wind farm-level controller in the wind farm and transmitted to a local controller at the wind turbine.

[0044] Technical Solution 16. A method for operating a power generation system that supplies active and reactive power to a power grid, the power generation system comprising a generator connected to power conversion components and dedicated reactive power compensation equipment, the method comprising:

[0045] Receive reactive power demands from the power generation system under its operating state and grid conditions; and

[0046] The reactive power of the power generation system and the terminal voltage of the generator are independently controlled by independent controllers of the reactive power compensation device and the power conversion component, respectively, in order to reduce the oscillating response of the reactive power output from the reactive power compensation device and the generator.

[0047] Technical Solution 17. The method according to Technical Solution 16, characterized in that it further includes:

[0048] The reactive power compensation device is operated in reactive power control mode via a device controller to generate at least a portion of the reactive power demand; and

[0049] The generator is operated in voltage control mode via a converter controller to control the terminal voltage of the generator, wherein the reactive power control mode of the reactive power compensation device does not interfere with the voltage control mode of the generator at the common coupling point of the power generation system.

[0050] Technical Solution 18. The method according to Technical Solution 17, characterized in that operating the reactive power compensation device in the reactive power control mode further includes:

[0051] Determine the maximum reactive power capacity of each of the power conversion component, the generator, and the reactive power compensation device; and

[0052] The supply of reactive power demand from the power conversion component, the generator, and / or the reactive power compensation device is coordinated by prioritizing the reactive power compensation device as a first reactive power source and prioritizing the generator and / or the power conversion component as a second reactive power source.

[0053] Technical Solution 19. The method according to Technical Solution 18, characterized in that, in the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation device, all the reactive power demand is supplied by the reactive power compensation device; and when the reactive power demand is greater than the maximum reactive power capacity of the reactive power compensation device, the maximum reactive power capacity of the reactive power compensation device is supplied; and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation device is allocated to the generator and / or the power conversion component.

[0054] Technical Solution 20. The method according to Technical Solution 16, characterized in that the power generation system includes a wind turbine, and the generator includes a doubly fed induction generator (DFIG).

[0055] It should be understood that methods and systems may also include any combination of additional features and / or steps described herein.

[0056] These and other features, aspects, and advantages of the invention will become more readily understood with reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. Attached Figure Description

[0057] The complete and feasible disclosure of the invention, including its best mode, is set forth in the description with reference to the accompanying drawings, which are intended for those skilled in the art.

[0058] Figure 1 A perspective view of one embodiment of a wind turbine according to the present disclosure is shown;

[0059] Figure 2 It shows the relationship with Figure 1 A schematic diagram of an embodiment of a wind turbine DFIG system used in conjunction with a wind turbine;

[0060] Figure 3 A schematic diagram of one embodiment of a power converter for a wind turbine according to the present disclosure is shown;

[0061] Figure 4 A schematic diagram depicting the active and reactive power flows in a wind turbine DFIG system according to various aspects of this disclosure is shown.

[0062] Figure 5 Figures are shown illustrating embodiments of a wind turbine controller according to various aspects of this disclosure;

[0063] Figure 6 Figures are shown illustrating alternative wind turbine controller embodiments according to various aspects of this disclosure;

[0064] Figure 7 A schematic diagram depicting various locations of reactive power compensation devices in a wind turbine DFIG system is shown;

[0065] Figure 8 A flowchart of one embodiment of the method according to this disclosure is shown;

[0066] Figure 9 A control scheme for an embodiment of the device controller of a power compensation device according to the present disclosure is shown; and

[0067] Figure 10 A flowchart of one embodiment of the method according to this disclosure is shown. Detailed Implementation

[0068] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not as a limitation thereof. Indeed, it will be apparent to those skilled in the art that various modifications and variations may be made to the invention without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used with another embodiment to produce yet another embodiment. Therefore, the invention is intended to cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0069] In general, this disclosure relates to a system and method for operating a power generation system supplying active and reactive power to a power grid, as discussed above, wherein the power generation system includes a generator with a power converter and a dedicated, separately integrated reactive power compensation device. The power generation system may be configured as a wind turbine with a DFIG system, wherein the wind turbine may be one of multiple wind turbines in a wind farm. Typically, the reactive power compensation device operates in either a reactive power control mode or a voltage control mode depending on the wind farm operating conditions. However, when the reactive power compensation device is integrated at the LSC and operates in voltage control mode, the device interacts with the voltage controller of the DFIG, resulting in an oscillating response of reactive power output from both the reactive power compensation device and the generator stator. Therefore, the method of this disclosure includes separating the control actions of the DFIG and the reactive power compensation device to reduce the oscillating response of reactive power output from the reactive power compensation device. The reactive power control mode of the reactive power compensation device's controller does not interfere with voltage control at the common point connected by the DFIG converter, ensuring no control interaction between the generator, power converter, and reactive power compensation device.

[0070] Furthermore, reactive power compensation equipment operating in reactive power control mode can achieve faster response during low voltage ride-through (LVRT) and / or high voltage ride-through (HVRT) events. This ensures the required reactive power injection under both normal and abnormal operating conditions. Moreover, due to direct reactive power control under both normal and abnormal operating conditions, the separation of reactive power control and voltage control between the generator and the reactive power compensation equipment provides a faster reactive power response for the equipment.

[0071] While not limited to such a configuration, for the purposes of explanation, this method and system aspect of the invention is described herein with reference to a wind turbine power generation system, and more particularly with a wind turbine DFIG system that supplies active and reactive power to the grid.

[0072] Now refer to the attached diagram, Figure 1A perspective view of one embodiment of a wind turbine 10 is shown. As shown, the wind turbine 10 typically 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 and extending outward 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 fewer than three rotor blades 22. Each rotor blade 22 may be spaced apart around the hub 20 to facilitate rotation of the rotor 18, thereby enabling kinetic energy to be converted from wind energy into usable mechanical energy, and subsequently into electrical energy. For example, as will be described below, the rotor 18 may be rotatably coupled to a generator 120 (…). Figure 2 ), used to generate electrical energy.

[0073] Wind power generation typically consists of a large number (usually 100 or more) of wind turbines 10 and associated wind turbine generators 120. Figure 2 The wind farm provides power for each individual wind turbine 10, where each individual wind turbine 10 typically experiences unique wind conditions. Therefore, the output power of each individual wind turbine generator 120 can vary from one wind turbine 10 to another within the wind farm.

[0074] As is generally understood, active power (P) and reactive power (Q) are generated by each wind turbine generator system (e.g., Figure 2 The system 100 depicted in the figure is provided. In some embodiments, a wind farm-level controller 177 ( Figure 5 The reactive power command (Qcmd) is provided to the wind turbine generator system based on the transmission grid demand (which may be specified by the grid operator or determined based on the grid voltage). The reactive power command may be the same for each wind turbine generator. In alternative control methods, the reactive power command may be individually tailored for each wind turbine generator 120 in the wind farm based on the different power generation characteristics of the respective wind turbine generator 120, as described, for example, in U.S. Patent Publication No. 2015 / 0295529. It should be understood that the present invention is not limited to the manner or method of generating reactive power commands for each wind turbine generator 120.

[0075] Now for reference Figure 2 This disclosure provides schematic diagrams of a wind turbine generator system as an implementation of a wind turbine DFIG power system 100 (“wind turbine system”) according to various aspects of this disclosure. Although this disclosure will be generally referenced herein... Figure 2 The system 100 shown is described herein, but those skilled in the art who use the disclosure provided herein should understand that aspects of this disclosure can also be applied to other power generation systems, and as mentioned above, the present invention is not limited to wind turbine systems.

[0076] exist Figure 2 In the embodiment, the wind turbine 10 ( Figure 1 The rotor 18 of the DFIG 120 can optionally be connected to a gearbox 118, which in turn is connected to a generator 120, which may be a doubly-fed induction generator (DFIG). Furthermore, as shown, the DFIG 120 can be connected to a stator bus 154. Additionally, as shown, a power conversion assembly 162 can be connected to the DFIG 120 via a rotor bus 156 and to the stator bus 154 via a line-side bus 188. Accordingly, the stator bus 154 is configured to provide multiphase power output (e.g., three-phase power) from the stator of the DFIG 120, and the rotor bus 156 provides multiphase power output (e.g., three-phase power) from the rotor of the DFIG 120. The power conversion assembly 162 may also include a rotor-side converter (RSC) 166 and a line-side converter (LSC) 168. Therefore, as shown, the DFIG 120 can be connected to the rotor-side converter 166 via the rotor bus 156. Additionally, RSC 166 is connected to LSC 168 via DC link 136, with DC link capacitor 138 spanning link 136. LSC 168 is then connected to line-side bus 188.

[0077] RSC 166 and LSC 168 can be configured for normal operating mode in a three-phase pulse-width modulation (PWM) arrangement using insulated-gate bipolar transistor (IGBT) switching elements, as referenced. Figure 3 To be discussed in more detail.

[0078] Furthermore, as shown in the figure, the power conversion assembly 162 can be coupled to the converter controller 174 to control the operation of the rotor-side converter 166 and the line-side converter 168. It should be noted that the converter controller 174 can be configured as an interface between the power conversion assembly 162 and the local wind turbine controller (control system) 176, and includes any number of control devices. In one embodiment, the controller 174 may include a processing device (e.g., a microprocessor, microcontroller, etc.) that executes computer-readable instructions stored in a computer-readable medium. When executed by the processing device, the instructions can cause the processing device to perform operations, including providing control commands (e.g., switching frequency commands) to the switching elements of the power conversion assembly 162.

[0079] As mentioned, for each DFIG wind turbine power generation system 100, reactive power is mainly supplied by RSC via generator 120 and LSC.

[0080] In a typical configuration, various line contactors and circuit breakers may also be included, including, for example, a grid circuit breaker 182, for isolating various components necessary for the normal operation of DFIG 120 during connection to and disconnection from loads such as grid 184. For example, a system circuit breaker 178 may connect system bus 160 to transformer 180, which may be connected to grid 184 via grid circuit breaker 182. In alternative embodiments, fuses may replace some or all of the circuit breakers.

[0081] In operation, the AC power generated at DFIG 120 by rotating rotor 18 is provided to grid 184 via a dual path defined by stator bus 154 and rotor bus 156. On rotor bus side 156, sinusoidal multiphase (e.g., three-phase) AC power is provided to power conversion assembly 162. Rotor-side power converter 166 converts the AC power provided from rotor bus 156 into direct current (DC) power and provides the DC power to DC link 136. As generally understood, the switching elements (e.g., IGBTs) used in the bridge circuit of rotor-side power converter 166 can be modulated to convert the AC power provided from rotor bus 156 into DC power suitable for DC link 136.

[0082] Furthermore, the line-side converter 168 converts the DC power on the DC link 136 into AC output power suitable for the power grid 184. Specifically, the switching elements (e.g., IGBTs) used in the bridge circuit of the line-side power converter 168 can be modulated to convert the DC power on the DC link 136 into AC power on the line-side bus 188. The AC power from the power conversion assembly 162 can be combined with the power from the stator of the DFIG 120 to provide multiphase power (e.g., three-phase power) with a frequency substantially maintained at the frequency of the power grid 184 (e.g., 50Hz or 60Hz).

[0083] Additionally, various circuit breakers and switches, such as grid circuit breaker 182, system circuit breaker 178, stator synchronizing switch 158, converter circuit breaker 186, and line contactor 172, may be included in the wind turbine power system 100 to connect or disconnect corresponding buses, for example, when excessive current may damage components of the wind turbine power system 100 or for other operational considerations. Additional protective components may also be included in the wind turbine power system 100.

[0084] Furthermore, the power conversion component 162 can receive control signals from, for example, a local control system 176 via the converter controller 174. These control signals can be based, in particular, on sensed conditions or operating characteristics of the wind turbine power system 100 and provide control over the operation of the power conversion component 162. For example, feedback in the form of sensed speed from the DFIG 120 can be used to control the conversion of output power from the rotor bus 156 to maintain an appropriate and balanced multiphase (e.g., three-phase) power source. Other feedback from other sensors can also be used by the controller 174 or the control system 176 to control the power conversion component 162, including, for example, stator and rotor bus voltage and current feedback. Using various forms of feedback information, switching control signals (e.g., gate timing commands for IGBTs), stator synchronization control signals, and circuit breaker signals can be generated.

[0085] The power conversion assembly 162 also compensates for or regulates the frequency of the three-phase power from the rotor in response to variations in wind speed, for example, at hub 20 and blades 22. Thus, the mechanical and electrical rotor frequencies are separated, and electrical stator and rotor frequency matching is facilitated substantially independently of the mechanical rotor speed.

[0086] In some cases, the bidirectional nature of the power conversion component 162, and specifically the bidirectional nature of LSC 168 and RSC 166, facilitates the feedback of at least some of the generated electrical power back to the generator rotor. More specifically, electrical power is transferred from stator bus 154 to line-side bus 188, and then via line contactor 172 into power conversion component 162, specifically LSC 168, which acts as a rectifier and rectifies the sinusoidal three-phase AC power into DC power. The DC power is then transferred to DC link 136. DC link capacitor 138 helps mitigate DC link voltage amplitude variations by mitigating DC ripple sometimes associated with three-phase AC rectification.

[0087] The DC power is then transmitted to RSC 166, which converts the DC power into three-phase sinusoidal AC power with predetermined voltage, current, and frequency. This conversion is monitored and controlled via converter controller 174. The converted AC power is then transmitted from RSC 166 to the generator rotor via rotor bus 156. In this way, reactive power control of the generator is facilitated by controlling the rotor current and voltage.

[0088] Now for reference Figure 3 According to various aspects of this disclosure, it is shown that Figure 2The diagram illustrates one embodiment of the power converter. As shown, the rotor-side converter (RSC) 166 includes multiple bridge circuits (e.g., H-bridge circuits), with each phase of the rotor bus 156 input to the rotor-side converter 166 connected to a single bridge circuit. Additionally, the line-side converter (LSC) 168 may also include multiple bridge circuits. Similar to the rotor-side converter 166, the line-side converter 168 also includes a single bridge circuit for each output phase of the line converter 168. In other embodiments, without departing from the scope of this disclosure, the line-side converter 168, the rotor-side converter 166, or both the line-side converter 168 and the rotor-side converter 166 may include parallel bridge circuits.

[0089] Each bridge circuit typically includes multiple switching elements (e.g., IGBTs) connected in series with each other. For example, as Figure 3 As shown, each bridge circuit includes an upper IGBT (e.g., IGBT 212) and a lower IGBT (e.g., IGBT 214). Additionally, diodes may be connected in parallel with each IGBT. In an alternative embodiment, parallel IGBTs and diodes may be used to increase the rated current of the converter. As generally understood, the line-side converter 168 and the rotor-side converter 166 may be controlled, for example, by providing control commands to the gates of the IGBTs using suitable drive circuitry. For example, the converter controller 174 may provide suitable gate timing commands to the gates of the IGBTs in the bridge circuit. The control commands may control the switching frequency of the IGBTs to provide the desired output. Those skilled in the art will understand that, as an alternative to the IGBTs, the power converter 162 may include any other suitable switching elements.

[0090] Now for reference Figure 4 A schematic diagram depicting the active (P) and reactive (Q) power flows in a wind turbine DFIG system 100 according to various aspects of this disclosure is shown. As understood in the art, the primary sources of reactive power in the DFIG system are from RSC 166 via generator 120 (generator stator-side reactive power (Qs)) and from RSC 166 via LSC 168 (generator line-side reactive power (Ql)). Furthermore, as shown, a harmonic distortion filter 175 can be configured in the line-side bus. Using power conversion components 162 (specifically RSC 166) to control the rotor current makes it possible to regulate the total reactive power (Qwtg) of the system 100 fed to the grid from RSC 166 independently of the rotational speed of generator 120. Furthermore, the DFIG 120 is capable of importing or exporting reactive power, which allows the system 100 to support the grid during periods of severe voltage fluctuations.

[0091] Still referencing Figure 4The wind turbine power system 100 includes a separate reactive power compensation device 200 (also referred to herein as a modular VAR box (MVB)) that generates auxiliary reactive power (Qmvb). In the depicted embodiment, the reactive power compensation device 200 may be connected to a line-side bus (with a harmonic distortion filter 175) such that (Qmvb) is combined with (Ql) on the line-side bus to form (Q), where (Q) and (Qs) are combined at a three-way transformer 202. Therefore, the total reactive power (Qwtg) from the wind turbine power system 100 is:

[0092] (Qwtg) = (Qs) + (Q), where

[0093] (Q) = (Ql) + (Qmvb)

[0094] Total reactive power (Qwtg) and total active power (Pwtg) are fed to the grid from transformer 202. Furthermore, the generator 120 and reactive power compensation device 200 described herein can each operate in reactive power control mode and voltage control mode based on the operating conditions of the wind turbine power system 100. The DFIG-based wind turbine with integrated MVB 200 at LSC 168 is configured to enhance wind turbine capabilities in several ways. For example, the reactive power contribution from the MVB 200 under steady-state conditions alleviates the reactive power compensation responsibility of RSC 166 and enables the DFIG 120 to generate more active power by operating at lower wind cut-in speeds. The dynamic reactive power reserve in the MVB 200 also enhances fault ride-through capability under varying grid conditions. In another embodiment, the MVB 200 can be connected to a grid or substation located remotely from the wind turbine or multiple wind turbines. In such an embodiment, the wind farm-level controller is configured to coordinate reactive power commands sent to the wind turbine and the MVB 200.

[0095] Figure 7 A diagram is provided depicting various operating locations of the reactive power compensation device 200 partially integrated with a separate wind turbine system 100. Dashed line "A" indicates that the reactive power compensation device 200 can be connected to the line-side bus 188 between LSC 168 and the three-way transformer 202. In this diagram, transformer 180 may be a substation transformer at the point of connection to the power grid (POI). Dashed line "B" indicates that the reactive power compensation device 200 can be connected (via transformer 204) downstream of the grid circuit breaker 182 (but immediately adjacent to the wind turbine system 100) or to bus 155 between the grid circuit breaker 182 and the three-way transformer 202. It should be understood that this disclosure is not limited to... Figure 7 The described integration location, and other suitable locations may be determined by those skilled in the art.

[0096] As mentioned, this method includes controlling a wind turbine 10 with a doubly fed induction generator (DFIG) system 120, wherein the wind turbine 10 may be one of multiple wind turbines in a wind farm that supplies active and reactive power to the grid. Therefore, refer to Figure 5 (Qcmd) is the reactive power demand, which is made to the wind turbine by the wind farm-level controller 177 within the wind farm and transmitted to the local controller 176 at the wind turbine 10. The local controller can then allocate (Qmvb) to the reactive power compensation device 200 (which may include a separate controller) and allocate (Qs) and (Ql) to the converter controller 174 to control the power conversion component 162 according to the corresponding reactive power demand.

[0097] Figure 6 In an alternative embodiment, the local wind turbine controller 176 receives a (Qcmd) request from the wind farm-level controller 177 and transmits the request to the power converter controller 174. The converter controller 174 allocates (Qmvb) to the reactive power compensation device 200 and controls the power conversion component 162 to generate (Qs) and (Ql).

[0098] It should be understood that the converter controller 174, the local wind turbine controller 176, and the wind farm-level controller 177 may each correspond to any suitable computing device and / or any combination of computing devices. For example, the controller may include one or more processors and one or more associated storage devices configured to perform various computer-implemented functions. As used herein, the term "processor" refers not only to an integrated circuit known in the art as contained in a computer, but also to a controller, microcontroller, microcomputer, programmable logic controller (PLC), application-specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) may generally include multiple 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 disc read-only memory (CD-ROM), magneto-optical disks (MOD), digital versatile discs (DVDs), and / or other suitable memory elements. Such memory devices(s) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the controller to perform various functions, such as the steps disclosed herein.

[0099] Now for reference Figure 8According to various aspects of this disclosure, flowcharts of embodiments of a method 300 for operating a power generation system are shown. Generally, method 300 is described herein as being implemented using a wind turbine system 100, such as the DFIG wind turbine power system 100 described above. However, it should be understood that the disclosed method 300 can be implemented using any other suitable power generation system configured to supply power (including reactive power) to loads such as a power grid. Furthermore, although for illustrative and discussion purposes, Figure 8 The steps described herein are executed in a specific order, but the methods described herein are not limited to any particular order or arrangement. Those skilled in the art will understand, using the disclosure provided herein, that the various steps of the methods can be omitted, rearranged, combined, and / or modified in various ways.

[0100] As shown in (302), method 300 includes receiving reactive power demands made by the wind turbine system 100 under operating and grid conditions. For example, in one embodiment, the reactive power demand may be determined by a wind farm-level controller 177 within the wind farm and transmitted to a local controller (e.g., controllers 174, 176) at the wind turbine 10. As shown in (304), method 300 includes decoupling reactive power control and voltage control between the generator 120 and the reactive power compensation device / MVB 200 to reduce the oscillating response of reactive power output from the reactive power compensation device 200 and the generator 120. As shown in (306), method 300 includes operating the MVB 200 in a reactive power control mode via device controller 206 to generate at least a portion of the reactive power demand.

[0101] For example, such as Figure 9 The diagram illustrates an MVB 200 operating in reactive power control mode. As shown, reactive power control mode typically refers to the current injection mode / Q control mode used for the MVB 200 to avoid control interaction between the MVB 200 and the DFIG 120. Therefore, as shown, during reactive power control mode, the device controller 206 may include a reactive power regulator 208 and a current regulator 210. Accordingly, the reactive power regulator 208 is configured to receive the reactive power demand (Qcmd) and the reactive power feedback signal (Qfbk) and determine the current command (Iycmd). The current regulator 210 is configured to receive the current command and the current feedback signal (Iyfbk) to generate a voltage command (Vcmd) for the MVB 200. Therefore, the voltage command (Vcmd) is configured to provide a portion (and in some cases, the majority) of the reactive power demand required by the wind farm under both normal and abnormal operating conditions. Furthermore, terminal voltage control is performed by the DFIG 120.

[0102] In an additional embodiment, the device controller 206 is configured to: determine the maximum reactive power capacity of each of the power conversion component 162, DFIG 120, and / or reactive power compensation device 200; and coordinate the supply of reactive power demand among the power conversion component 162, DFIG 120, and / or reactive power compensation device 200, for example, by prioritizing the reactive power compensation device 200 as a first reactive power source and prioritizing the DFIG 120 and / or power conversion component 162 as a second reactive power source.

[0103] In one embodiment, for example, during the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation device 200, all reactive power demand can be supplied by the reactive power compensation device 200. Alternatively, during the coordination step, when the reactive power demand is greater than the maximum reactive power capacity of the reactive power compensation device 200, the maximum reactive power capacity of the reactive power compensation device 200 can be supplied, and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation device 200 can be allocated to DFIG 120.

[0104] In another embodiment, the maximum reactive power capacity of the DFIG 120 and the reactive power compensation device 200 may be determined, for example, by their respective controllers based on any one or a combination of power system operating conditions, ambient temperature or generator thermal constraints, power conversion component rating limits, or reactive power compensation device rating limits. In an additional embodiment, the maximum reactive power capacity of the power conversion component 162, the DFIG 120, and / or the reactive power compensation device 200 may be determined continuously or periodically by their respective controllers.

[0105] Return to reference Figure 8 As shown in (308), method 300 includes operating DFIG 120 in voltage control mode via converter controller 174 to control the terminal voltage of DFIG 120. Accordingly, the reactive power control mode of reactive power compensation device 200 does not interfere with the voltage control mode of DFIG 120 at the point of common coupling of generation system 100. In other words, method 200 of this disclosure proposes a separate control strategy, wherein most of the reactive power demand required by the wind farm is allocated to MVB 200, and MVB 200 operates in reactive power control mode under both normal and abnormal operating conditions. Since the two different controllers separate the control objectives, there is no control interaction. Furthermore, no modifications are required in DFIG control. In addition, the system and method of this disclosure provide a faster reactive power response from MVB 200.

[0106] Now for reference Figure 10According to various aspects of this disclosure, a flowchart of another embodiment of a method 400 for operating a power generation system is shown. Generally, method 400 is described herein as being implemented using a wind turbine system 100, such as the DFIG wind turbine power system 100 described above. However, it should be understood that the disclosed method 400 can be implemented using any other suitable power generation system configured to supply power (including reactive power) for application to loads such as the power grid. Furthermore, although for illustrative and discussion purposes, Figure 10 The steps described herein are executed in a specific order, but the methods described herein are not limited to any particular order or arrangement. Those skilled in the art will understand, using the disclosure provided herein, that the various steps of the methods can be omitted, rearranged, combined, and / or modified in various ways.

[0107] As shown in (402), method 400 includes receiving reactive power demands made by the power generation system 10 under both the operating state of the power generation system and the grid state. As shown in (404), method 400 includes independently controlling the reactive power of the power generation system 100 and the terminal voltage of the generator 120 via separate controllers of the reactive power compensation device 200 and the power conversion component 162, respectively, to reduce the oscillating response of the reactive power output from the reactive power compensation device 200 and the generator 120. Therefore, interaction between the voltage controller of the reactive power compensation device 200 and the power conversion component 162 is prevented, thereby reducing the oscillating response of the reactive power output of both the reactive power compensation device 200 and the generator.

[0108] Various aspects and embodiments of the present invention are defined by the following numbered clauses:

[0109] Clause 1. A method for operating a power generation system that supplies active and reactive power to a power grid, the power generation system comprising a generator connected to a power conversion component and a dedicated reactive power compensation device, the power conversion component and the reactive power compensation device comprising a converter controller and a device controller, respectively, the method comprising:

[0110] Receive reactive power demands from the power generation system under its operating and grid conditions;

[0111] Separating reactive power control and voltage control between the generator and the reactive power compensation equipment reduces the oscillating response of the reactive power output from both the equipment and the generator; and

[0112] The reactive power compensation device is operated in reactive power control mode via the equipment controller to generate at least a portion of the reactive power demand.

[0113] Clause 2. The method according to Clause 1 further includes: operating the generator in a voltage control mode via a converter controller to control the terminal voltage of the generator, wherein the reactive power control mode of the reactive power compensation device does not interfere with the voltage control mode of the generator at the point of common coupling of the power generation system.

[0114] Clause 3. The method described in Clause 2, wherein operating the reactive power compensation device in reactive power control mode further includes:

[0115] Determine the maximum reactive power capacity of each of the power conversion components, generators, and reactive power compensation equipment; and

[0116] The supply of reactive power demand from power conversion components, generators, and / or reactive power compensation equipment is coordinated by prioritizing reactive power compensation equipment as the first reactive power source and prioritizing generators and / or power conversion components as the second reactive power source.

[0117] Clause 4. The method described in Clause 3, wherein, in the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation equipment, all reactive power demand is supplied by the reactive power compensation equipment.

[0118] Clause 5. The method according to Clause 3, wherein, in the coordination step, when the reactive power demand is greater than the maximum reactive power capacity of the reactive power compensation equipment, the maximum reactive power capacity of the reactive power compensation equipment is supplied, and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation equipment is allocated to the generator and / or power conversion components.

[0119] Clause 6. The method described in Clause 3, wherein the maximum reactive power capacity of the power conversion components, generators and / or reactive power compensation devices is determined based on any one or a combination of the power system operating conditions, ambient temperature or thermal constraints of the generator, power conversion component rating limits or reactive power compensation device rating limits.

[0120] Clause 7. The method described in Clause 3, wherein the maximum reactive power capacity of the power conversion components, generators and / or reactive power compensation equipment is determined continuously or periodically.

[0121] Clause 8. The method described in Clauses 1 to 7, wherein the power generation system includes a wind turbine and the generator includes a doubly fed induction generator (DFIG).

[0122] Clause 9. The method according to Clause 8, wherein the wind turbine is one of a plurality of wind turbines in a wind farm that supplies active and reactive power to the grid, and wherein the reactive power demand is determined by a wind farm-level controller within the wind farm and transmitted to a local controller at the wind turbine.

[0123] Clause 10. A wind turbine system configured to supply active and reactive power to a power grid, the wind turbine system comprising:

[0124] A wind turbine, which includes a rotor, a hub, and multiple rotor blades connected to the hub;

[0125] A doubly fed induction generator (DFIG) system coupled to a rotor, the DFIG system comprising a generator coupled to power conversion components having a line-side converter (LSC) and a rotor-side converter (RSC), and a converter controller;

[0126] A reactive power compensation device, operably configured with a DFIG system to generate reactive power, the reactive power compensation device including a device controller configured to:

[0127] Receive reactive power demands from the wind turbine system under both its operating and grid conditions; and

[0128] Separate reactive power control and voltage control between the generator and the reactive power compensation equipment to reduce the oscillating response of reactive power output from the reactive power compensation equipment and the generator.

[0129] Clause 11. The wind turbine system according to Clause 10, wherein the equipment controller is further configured to operate the reactive power compensation equipment in a reactive power control mode to generate at least a portion of the reactive power demand.

[0130] Clause 12. The wind turbine system according to Clause 11, wherein the converter controller is configured to operate the generator in a voltage control mode to control the generator's terminal voltage, wherein the reactive power control mode of the reactive power compensation device does not interfere with the generator's voltage control mode at the point of common coupling of the power generation system.

[0131] Clause 13. The wind turbine system pursuant to Clause 11, wherein the equipment controller is further configured to:

[0132] Determine the maximum reactive power capacity of each of the power conversion components, generators, and reactive power compensation equipment; and

[0133] The supply of reactive power demand from power conversion components, generators, and / or reactive power compensation equipment is coordinated by prioritizing reactive power compensation equipment as the first reactive power source and prioritizing generators and / or power conversion components as the second reactive power source.

[0134] Clause 14. The wind turbine system as described in Clause 13, wherein the maximum reactive power capacity of the power conversion components, generator and / or reactive power compensation equipment is determined based on any one or a combination of the power system operating conditions, ambient temperature or thermal constraints of the generator, power conversion component rating limits or reactive power compensation equipment rating limits.

[0135] Clause 15. The wind turbine system according to Clauses 10 to 14, wherein the wind turbine is one of a plurality of wind turbines in a wind farm that supplies active and reactive power to the grid, and wherein the reactive power demand is determined by a wind farm-level controller within the wind farm and transmitted to a local controller at the wind turbine.

[0136] Clause 16. A method for operating a power generation system that supplies active and reactive power to a power grid, the power generation system comprising a generator coupled to power conversion components and dedicated reactive power compensation equipment, the method comprising:

[0137] Receive reactive power demands from the power generation system under its operating and grid conditions; and

[0138] The reactive power of the power generation system and the terminal voltage of the generator are independently controlled by separate controllers of the reactive power compensation equipment and the power conversion component, in order to reduce the oscillating response of the reactive power output from the reactive power compensation equipment and the generator.

[0139] Clause 17. The method described pursuant to Clause 16 further includes:

[0140] The reactive power compensation equipment is operated in reactive power control mode via the equipment controller to generate at least a portion of the reactive power demand; and

[0141] The generator is operated in voltage control mode via the converter controller in order to control the generator's terminal voltage. The reactive power control mode of the reactive power compensation device does not interfere with the generator's voltage control mode at the point of common coupling of the power generation system.

[0142] Clause 18. The method according to Clause 17, wherein operating the reactive power compensation device in reactive power control mode further includes:

[0143] Determine the maximum reactive power capacity of each of the power conversion components, generators, and reactive power compensation equipment; and

[0144] The supply of reactive power demand from power conversion components, generators, and / or reactive power compensation equipment is coordinated by prioritizing reactive power compensation equipment as the first reactive power source and prioritizing generators and / or power conversion components as the second reactive power source.

[0145] Clause 19. The method according to Clause 18, wherein, in the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation equipment, all reactive power demand is supplied by the reactive power compensation equipment, and when the reactive power demand is greater than the maximum reactive power capacity of the reactive power compensation equipment, the maximum reactive power capacity of the reactive power compensation equipment is supplied, and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation equipment is allocated to the generator and / or power conversion components.

[0146] Clause 20. The method described in Clause 16, wherein the power generation system includes a wind turbine and the generator includes a doubly fed induction generator (DFIG).

[0147] This written description uses examples to disclose the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any incorporated methods. The patentability of the invention is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims.

Claims

1. A method for operating a power generation system that supplies active and reactive power to a power grid, the power generation system comprising a generator connected to a power conversion component and a dedicated reactive power compensation device, the power conversion component and the reactive power compensation device each comprising a converter controller and a device controller, the method comprising: Receive reactive power demands from the power generation system under the operating state and grid state of the power generation system; The reactive power control and voltage control between the generator and the reactive power compensation device are separated in order to reduce the oscillating response of the reactive power output from the reactive power compensation device and the generator; The reactive power compensation device is operated in reactive power control mode via the device controller to generate at least a portion of the reactive power demand; and The generator is operated in voltage control mode via the converter controller to control the generator's terminal voltage, wherein the reactive power control mode of the reactive power compensation device does not interfere with the generator's voltage control mode at the point of common coupling of the power generation system. The operation of the reactive power compensation device under the reactive power control mode also includes: Determine the maximum reactive power capacity of each of the power conversion component, the generator, and the reactive power compensation device; and The supply of reactive power demand from the power conversion component, the generator, and / or the reactive power compensation device is coordinated by prioritizing the reactive power compensation device as a first reactive power source and prioritizing the generator and / or the power conversion component as a second reactive power source.

2. The method according to claim 1, characterized in that, In the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation device, all the reactive power demand is supplied by the reactive power compensation device.

3. The method according to claim 1, characterized in that, In the coordination step, when the reactive power demand exceeds the maximum reactive power capacity of the reactive power compensation device, the maximum reactive power capacity of the reactive power compensation device is supplied, and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation device is allocated to the generator and / or the power conversion component.

4. The method according to claim 1, characterized in that, The maximum reactive power capacity of the power conversion component, the generator, and / or the reactive power compensation device is determined based on any one or a combination of the power system operating conditions, ambient temperature, thermal constraints of the generator, rating limits of the power conversion component, or rating limits of the reactive power compensation device.

5. The method according to claim 1, characterized in that, The maximum reactive power capacity of the power conversion component, the generator, and / or the reactive power compensation device is determined continuously or periodically.

6. The method according to claim 1, characterized in that, The power generation system includes a wind turbine, and the generator includes a doubly fed induction generator (DFIG).

7. The method according to claim 6, characterized in that, The wind turbine is one of multiple wind turbines in a wind farm that supplies active and reactive power to the power grid, wherein the reactive power demand is determined by a wind farm-level controller within the wind farm and transmitted to a local controller at the wind turbine.

8. A wind turbine system configured to supply active and reactive power to a power grid, the wind turbine system comprising: A wind turbine, comprising a rotor, a hub, and a plurality of rotor blades connected to the hub; A doubly fed induction generator (DFIG) system coupled to the rotor, the DFIG system comprising a generator coupled to power conversion components having a line-side converter (LSC), a rotor-side converter (RSC), and a converter controller; A reactive power compensation device, operably configured with the DFIG system to generate reactive power, the reactive power compensation device including a device controller configured to: Receive reactive power demands from the wind turbine system under its operating state and grid conditions; The reactive power compensation device is operated in reactive power control mode to generate at least a portion of the reactive power demand; and The reactive power control and voltage control between the generator and the reactive power compensation device are separated in order to reduce the oscillating response of the reactive power output from the reactive power compensation device and the generator. The converter controller is configured to operate the generator in a voltage control mode to control the generator's terminal voltage, wherein the reactive power control mode of the reactive power compensation device does not interfere with the generator's voltage control mode at the common coupling point of the DFIG system. The device controller is further configured to: Determine the maximum reactive power capacity of each of the power conversion component, the generator, and the reactive power compensation device; and The supply of reactive power demand from the power conversion component, the generator, and / or the reactive power compensation device is coordinated by prioritizing the reactive power compensation device as a first reactive power source and prioritizing the generator and / or the power conversion component as a second reactive power source.

9. The wind turbine system according to claim 8, characterized in that, The maximum reactive power capacity of the power conversion component, the generator, and / or the reactive power compensation device is determined based on any one or a combination of the power system operating conditions, ambient temperature, thermal constraints of the generator, rating limits of the power conversion component, or rating limits of the reactive power compensation device.

10. The wind turbine system according to claim 8, characterized in that, The wind turbine is one of multiple wind turbines in a wind farm that supplies active and reactive power to the power grid, wherein the reactive power demand is determined by a wind farm-level controller within the wind farm and transmitted to a local controller at the wind turbine.

11. A method for operating a power generation system that supplies active and reactive power to a power grid, the power generation system comprising a generator connected to power conversion components and dedicated reactive power compensation equipment, the method comprising: Receive reactive power demands from the power generation system under the operating state and grid state of the power generation system; The reactive power of the power generation system and the terminal voltage of the generator are independently controlled by separate controllers of the reactive power compensation device and the power conversion component, respectively, in order to reduce the oscillating response of the reactive power output from the reactive power compensation device and the generator; The reactive power compensation device is operated in reactive power control mode via the device controller to generate at least a portion of the reactive power demand; and The generator is operated in voltage control mode via a converter controller to control the generator's terminal voltage, wherein the reactive power control mode of the reactive power compensation device does not interfere with the generator's voltage control mode at the point of common coupling of the power generation system. The operation of the reactive power compensation device under the reactive power control mode also includes: Determine the maximum reactive power capacity of each of the power conversion component, the generator, and the reactive power compensation device; and The supply of reactive power demand from the power conversion component, the generator, and / or the reactive power compensation device is coordinated by prioritizing the reactive power compensation device as a first reactive power source and prioritizing the generator and / or the power conversion component as a second reactive power source.

12. The method according to claim 11, characterized in that, In the coordination step, when the reactive power demand is less than the maximum reactive power capacity of the reactive power compensation device, all the reactive power demand is supplied by the reactive power compensation device; and when the reactive power demand is greater than the maximum reactive power capacity of the reactive power compensation device, the maximum reactive power capacity of the reactive power compensation device is supplied, and the deficit between the reactive power demand and the maximum reactive power capacity of the reactive power compensation device is allocated to the generator and / or the power conversion component.

13. The method according to claim 11, characterized in that, The power generation system includes a wind turbine, and the generator includes a doubly fed induction generator (DFIG).

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