System and method for providing grid forming control for a doubly-fed wind turbine generator

Abstract

A method for providing grid formation control of a doubly-fed generator of a wind turbine includes receiving one or more voltage commands from an external controller via a stator voltage regulator of a converter controller. Further, the method includes determining one or more rotor current commands from a magnetizing current command and a stator current feedback signal of the doubly-fed generator via the stator voltage regulator. Accordingly, the method includes using the one or more rotor current commands to control a rotor voltage of the doubly-fed generator to achieve the one or more voltage commands.

Description

Technical Field

[0001] This disclosure generally relates to wind turbines, and more particularly to systems and methods for providing grid formation control for doubly-fed wind turbine generators. Background Technology

[0002] Wind power is considered one of the cleanest and most environmentally friendly energy sources available today, and wind turbines are receiving increasing attention in this area. A modern wind turbine typically consists of a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture the kinetic energy of the wind using the known airfoil principle. For example, rotor blades typically have an airfoil cross-sectional profile, such that during operation, air flowing over the blades creates a pressure difference between the sides. Therefore, lift, directed from the pressure side towards the suction side, acts on the blades. This lift generates torque on the main rotor shaft, which is typically geared to the generator to produce electricity.

[0003] Wind turbines can be classified into two types: constant-speed turbines and variable-speed turbines. Conventionally, 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. Conventional current source control of wind turbines is based on the assumption that the grid voltage waveform is a fundamental voltage waveform with a fixed frequency and amplitude, and that wind power penetration in the grid is low enough 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 fundamental voltage waveform. However, with the rapid growth of wind power, its penetration in some grids has increased to the point where wind turbine generators have a significant impact on grid voltage and frequency. When a wind turbine is located in a weak grid, wind turbine power fluctuations can lead to increased variations in the amplitude and frequency of the grid voltage. These fluctuations can adversely affect the performance and stability of the PLL and the wind turbine current control.

[0004] Furthermore, many existing renewable energy converters, such as doubly-fed wind turbines, operate in "grid-following" mode. Grid-following devices utilize fast current regulation loops to control the active and reactive power exchanged with the grid. More specifically, Figure 1The diagram illustrates the basic components of the main circuit and converter control structure of a grid-following doubly-fed induction generator (DFIG) wind turbine. As shown, the active power reference for the converter is generated by an energy source regulator (e.g., the turbine control section of the wind turbine). This is passed as a torque reference, representing the smaller of the maximum power available from the energy source at that moment or a reduction command from a higher-level grid controller. The converter controller then determines the current reference for the active component of the current to achieve the desired torque. Therefore, the DFIG wind turbine includes the function of managing voltage and reactive power in a manner that generates commands for the reactive component of the current. A wide-bandwidth current regulator then develops the commands by which the converter applies voltage to the system, such that the actual current closely follows the commands.

[0005] Alternatively, a grid-forming converter provides voltage source characteristics, where the angle and amplitude of the voltage are controlled to achieve the regulation functions required by the grid. In this configuration, current flows according to grid demand, while the converter helps establish voltage and frequency for the grid. This characteristic is comparable to that of a conventional generator based on a turbine driving a synchronous motor. Therefore, a grid forming source must include the following basic functions: (1) support grid voltage and frequency for any current (both active and reactive) within the rated value of the equipment; (2) prevent operation beyond the voltage or current capacity of the equipment by allowing changes in grid voltage or frequency rather than disconnecting the equipment (disconnection is only allowed when the voltage or frequency exceeds the boundary established by the grid entity); (3) maintain stability for any grid configuration or load characteristics, including serving isolated loads or connecting to other grid forming sources, and switching between these configurations; (4) share the total load of the grid among other grid forming sources connected to the grid; (5) traverse grid disturbances (both large and small disturbances); and (6) meet requirements (1)-(5) without requiring rapid communication with other control systems present in the grid or externally created logic signals related to changes in grid configuration.

[0006] The basic control structure for achieving the aforementioned grid formation goals was developed in the early 1990s and field-proven for battery systems (see, for example, U.S. Patent No. 5,798,633 entitled "Battery Energy Storage PowerConditioning System"). Applications to all-converter wind turbines and solar generators are disclosed in U.S. Publication No. 2010 / 0142237 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". However, such implementations have already been adopted in all-converter wind turbines.

[0007] In view of the foregoing, systems and methods for solving the aforementioned problems are welcome in the art. Therefore, this disclosure relates to a system and method for applying grid formation control to a doubly-fed wind turbine generator. Summary of the Invention

[0008] 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.

[0009] In one aspect, this disclosure relates to a method for providing grid formation control for a doubly-fed generator (DFIG) for a wind turbine. The method includes receiving one or more voltage commands via a stator voltage regulator of a converter controller. Furthermore, the method includes determining one or more rotor current commands via the stator voltage regulator based on a magnetizing current command and a stator current feedback signal from the DFIG. Therefore, the method includes using the one or more rotor current commands to control the rotor voltage of the DFIG to achieve the one or more voltage commands.

[0010] In embodiments, the voltage commands(s) may include, for example, a stator voltage amplitude command and / or a stator voltage angle command. More specifically, in embodiments, the method may include determining the voltage commands(s) ...

[0011] In another embodiment, the method may include receiving one or more reference commands from an external controller. In such an embodiment, the external controller may include a turbine controller for a wind turbine or a field-level controller for a wind farm, the wind farm comprising wind turbines and at least one additional wind turbine.

[0012] In another embodiment, the reference commands may include at least one of a voltage reference or a reactive current-voltage reference from the field-level controller or a power reference from the turbine controller.

[0013] In an embodiment, the method may include: converting (a plurality of) voltage commands into stator voltage commands via a stator voltage regulator; determining a magnetizing current feedforward signal via the stator voltage regulator based on the stator voltage commands and magnetization admittance, the magnetizing current feedforward signal facilitating a rapid response of the stator voltage to the stator voltage commands; and adding the magnetizing current feedforward signal to a magnetizing current correction signal to determine a magnetizing current command.

[0014] In an additional embodiment, the method may include: receiving a stator voltage feedback signal; determining the difference between the stator voltage feedback signal and the stator voltage command; and determining a magnetizing current correction signal via a proportional-integral regulator.

[0015] In another embodiment, the method may include adaptively fine-tuning the magnetization admittance by calculating the effective admittance based on the stator voltage feedback signal and the magnetization current command. More specifically, in an embodiment, calculating the effective admittance based on the stator voltage feedback signal and the magnetization current command may include: determining the absolute value of the magnetization current command; inverting the sign of the absolute value of the magnetization current command (e.g., from negative to positive or from positive to negative) to obtain a magnetization current value; determining the absolute value of the stator voltage feedback signal; dividing the magnetization current value by the absolute value of the stator voltage feedback signal to obtain a quotient; and filtering the quotient to remove noise and determine the effective admittance. In such an embodiment, the response of the effective admittance may be slower than the response of the magnetization current correction signal.

[0016] In another embodiment, determining the rotor current command(s) based on the magnetizing current command and the stator current feedback signal of the doubly-fed generator may include adding the magnetizing current command to the stator current feedback signal.

[0017] In other embodiments, controlling the rotor voltage of a doubly-fed generator using one or more voltage commands may include sending one or more rotor current regulator commands to a rotor current regulator of a converter controller via a stator voltage regulator, the converter controller providing control of the rotor voltage of the doubly-fed generator via a rotor-side power converter.

[0018] In another aspect, this disclosure relates to a converter controller for providing grid formation control for a doubly-fed generator (DFIG) of a wind turbine. The converter controller includes at least a stator voltage regulator having at least one processor. The processor(s) are configured to perform multiple operations, including but not limited to: receiving one or more voltage commands; determining one or more rotor current commands based on a magnetizing current command and a stator current feedback signal from the DFIG; and controlling the rotor voltage of the DFIG using the one or more rotor current commands to implement the one or more voltage commands. It should be understood that the converter controller may also include any of the additional features described herein.

[0019] In another aspect, this disclosure relates to a method for providing grid formation control for a doubly-fed generator (DFIG) for a wind turbine. The method includes measuring a stator current signal of the DFIG. Furthermore, the method includes feeding the stator current signal into a rotor current command of the DFIG to substantially decouple the stator response stator voltage from one or more grid characteristics. Additionally, the method includes controlling the rotor voltage of the DFIG using the rotor current command. It should be understood that the method may also include any of the additional features and / or steps described herein.

[0020] 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 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

[0021] 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.

[0022] Figure 1 The diagram shows a single-line diagram of a conventionally constructed doubly-fed wind turbine generator, which has a converter control structure for grid-following applications.

[0023] Figure 2 The figure is a perspective view of one embodiment of a wind turbine according to the present disclosure;

[0024] Figure 3 The figure shows a simplified interior view of a cabin according to an embodiment of the present disclosure;

[0025] Figure 4 The diagram is suitable for use with Figure 1 A schematic diagram of one embodiment of a wind turbine electric power system used in conjunction with the wind turbines shown in the figure;

[0026] Figure 5The figure is a schematic diagram of an embodiment of a wind farm with multiple wind turbines according to the present disclosure;

[0027] Figure 6 The figure shows a block diagram of one embodiment of the controller according to the present disclosure;

[0028] Figure 7 The figure shows a single-line diagram of a doubly-fed wind turbine generator with converter control for grid forming applications according to the present disclosure.

[0029] Figure 8 The figure shows a flowchart of one embodiment of a method for providing grid formation control for a doubly-fed generator for a wind turbine, according to the present disclosure;

[0030] Figure 9 The figure shows a schematic diagram of a simplified equivalent circuit of a doubly-fed wind turbine generator according to the present disclosure.

[0031] Figure 10 The figure is a schematic diagram of an embodiment of the logic for creating rotor current commands for stator voltage regulation according to the present disclosure.

[0032] Figure 11 The figure is a schematic diagram of an embodiment of the logic for creating an effective value of magnetization admittance for the predictive portion of the control of a doubly-fed wind turbine generator according to the present disclosure. Detailed Implementation

[0033] Reference will now be made in detail to embodiments of the invention, one or more of which are illustrated in the accompanying drawings. Each example is provided by way of explanation rather than limitation of the invention. 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 illustrated or described in part as one embodiment may be used with another embodiment to produce yet another embodiment. Therefore, the invention is intended to cover such modifications and variations and their equivalents as fall within the scope of the appended claims.

[0034] Generally, this disclosure relates to systems and methods for providing grid formation control for doubly-fed induction generator (DFIG) wind turbine generators. More specifically, the systems described herein include grid formation controls, such as inertial power regulators and terminal voltage regulators, which provide performance similar to synchronous generators and have the ability to set parameters as needed to meet grid requirements. These grid formation controls develop commands for the magnitude and angle of the voltage at the source side of the transformer connected to the grid. Therefore, the systems and methods of this disclosure implement voltage commands generated by grid formation control in DFIG wind turbine generators. In previous applications, voltage was achieved directly through a power electronic converter, while in DFIG wind turbine generators, voltage must be achieved indirectly via rotor voltage control. Therefore, this disclosure, its systems, and methods include an inner-loop current regulator structure and a fast stator voltage regulator to translate voltage commands from grid formation control into rotor current regulator commands.

[0035] Now refer to the attached diagram, Figure 2 The figure shows a perspective view of one embodiment of a wind turbine 10 according to the present disclosure. 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 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 into usable mechanical energy, and subsequently into electrical energy. For example, the hub 20 may be rotatably coupled to a generator 24 positioned within the nacelle 16. Figure 3 This allows for the generation of electrical energy.

[0036] 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 outside the wind turbine 10. Furthermore, the controller 26 may be communicatively coupled to any number of components of the wind turbine 10 to control the operation of such components and / or to perform corrective or control actions. Accordingly, the controller 26 may include a computer or other suitable processing unit. Therefore, in several embodiments, the controller 26 may include suitable computer-readable instructions that, when executed, configure the controller 26 to perform various functions, such as receiving, sending, and / or executing wind turbine control signals. Thus, the controller 26 may be generally configured to control various operating modes of the wind turbine 10 (e.g., start-up or shutdown sequences), derating or boosting of the wind turbine, and / or various components of the wind turbine 10.

[0037] Now for reference Figure 2 The illustration shows Figure 1 The diagram shows a simplified internal view of one embodiment of the nacelle 16 of the wind turbine 10. As shown, a generator 24 may be housed within the nacelle 16 and supported on top of a base plate 46. Generally, the generator 24 may be coupled to a rotor 18 to generate 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 a hub 20 for rotation therewith. The rotor shaft 34 may then be rotatably coupled to a generator shaft 36 of the generator 24 via a gearbox 38. As generally understood, the rotor shaft 34 may provide a low-speed, high-torque input to the gearbox 38 in response to rotation of the rotor blades 22 and the hub 20. 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, consequently, the generator 24.

[0038] The wind turbine 10 may also include one or more pitch drive mechanisms 32 communicatively coupled to the wind turbine controller 26, wherein each (multiple) pitch control mechanism 32 is configured to rotate the pitch bearing 40, and thus to rotate the respective rotor blades 22 about their respective pitch axis 28. Furthermore, 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 the yaw bearing 44 of the wind turbine 10 disposed between the nacelle 16 and the tower 12 of the wind turbine 10).

[0039] In addition, the wind turbine 10 may include one or more sensors 66, 68 for monitoring various wind conditions of the wind turbine 10. For example, the incoming wind direction 52, wind speed, or any other suitable wind conditions near the wind turbine 10 may be measured by using a suitable weather sensor 66. Suitable weather sensors may include, for example, light detection and ranging (“LIDAR”) devices, sound detection and ranging (“SODAR”) devices, anemometers, wind vanes, barometers, radar devices (such as Doppler radar devices), or any other sensing devices now known in the art or developed hereafter that can provide wind direction information. Additional sensors 68 may be used to measure additional operating parameters of the wind turbine 10, such as voltage, current, vibration, etc., as described herein.

[0040] Now for reference Figure 4 A schematic diagram of one embodiment of a wind turbine power system 100 is illustrated according to various aspects of this disclosure. Although this disclosure will be generally referenced herein... Figure 4The system 100 shown herein is described, 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 invention is not limited to wind turbine systems.

[0041] exist Figure 4 In the embodiments described above, the wind turbine 10 ( Figure 2 The rotor 18 of the DFIG 102 can optionally be connected to a gearbox 38, which in turn is connected to a generator 102, which may be a doubly-fed induction generator (DFIG). As shown, the DFIG 102 can be connected to a stator bus 104. Furthermore, 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. Accordingly, the stator bus 104 can provide multiphase output power (e.g., three-phase power) from the stator of the DFIG 102, and the rotor bus 108 can provide multiphase output 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 connected to the rotor-side converter 112 via the rotor bus 108. Additionally, RSC 112 is connected to LSC 114 via DC link 116, with DC link capacitor 118 spanning link 116. LSC 114 is then connected to line-side bus 110.

[0042] RSC 112 and LSC 114 can be configured for normal operating modes in a three-phase pulse-width modulation (PWM) arrangement using one or more switching devices such as insulated-gate bipolar transistors (IGBTs). Furthermore, power converter 106 can be coupled to converter controller 120 to control the operation of rotor-side converter 112 and line-side converter 114, as described herein. It should be noted that converter controller 120 can be configured as an interface between power converter 106 and turbine controller 26, and can include any number of control devices.

[0043] In a typical configuration, various line contactors and circuit breakers may also be included, including, for example, a grid circuit breaker 122, for isolating various components necessary for the normal operation of DFIG 102 during connection to and disconnection from loads such as power grid 124. For example, a system circuit breaker 126 may connect system bus 128 to transformer 130, which may be connected to power grid 124 via grid circuit breaker 122. In alternative embodiments, fuses may replace some or all of the circuit breakers.

[0044] In operation, the AC power generated at DFIG 102 by rotating rotor 18 is provided to power grid 124 via a dual path defined by stator bus 104 and rotor bus 108. On rotor bus side 108, sinusoidal multiphase (e.g., three-phase) AC power is provided to power converter 106. Rotor-side power converter 112 converts the AC power provided from rotor bus 108 into direct current (DC) power and provides the DC power to DC link 116. As generally understood, the switching elements (e.g., IGBTs) used in the bridge circuit of rotor-side power converter 112 can be modulated to convert the AC power provided from rotor bus 108 into DC power suitable for DC link 116.

[0045] Furthermore, the line-side converter 114 converts the DC power on the DC link 116 into AC output power suitable for the power grid 124. Specifically, 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 multiphase power (e.g., three-phase power) with a frequency substantially maintained at the frequency of the power grid 124 (e.g., 50Hz or 60Hz).

[0046] Additionally, various circuit breakers and switches, such as grid circuit breaker 122, system circuit breaker 126, stator synchronizing switch 132, converter circuit breaker 134, and line contactor 136, 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.

[0047] Furthermore, the power converter 106 may receive control signals from, for example, a local control system 176 via the converter controller 120. These control signals may be based, in particular, on sensed state or operating characteristics of the wind turbine power system 100. Typically, the control signals provide control for the operation of the power converter 106. For example, feedback in the form of sensed speed of the DFIG 102 may be used to control the conversion of output power from the rotor bus 108 to maintain an appropriate and balanced multiphase (e.g., three-phase) power source. Other feedback from other sensors may also be used by the controllers(s) 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, switching control signals (e.g., gate timing commands for IGBTs), stator synchronization control signals, and circuit breaker signals may be generated.

[0048] The power converter 106 also compensates for or regulates the frequency of the three-phase power from the rotor to accommodate variations in wind speed, such as at the 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 independently of the mechanical rotor speed.

[0049] In some states, the bidirectional nature of power converter 106, and specifically the bidirectional nature of LSC 114 and RSC 112, facilitates the feedback of at least some of the generated electrical power back to the generator rotor. More specifically, electrical power can be transferred from stator bus 104 to line-side bus 110, and then via line contactor 136 and into power converter 106 (specifically LSC 114, which acts as a rectifier and rectifies the sinusoidal three-phase AC power into DC power). The DC power is transferred to DC link 116. Capacitor 118 helps mitigate DC link voltage amplitude variations by facilitating the reduction of DC ripple sometimes associated with three-phase AC rectification.

[0050] The DC power is then transmitted to RSC 112, which converts the DC power into three-phase sinusoidal AC power by adjusting the voltage, current, and frequency. This conversion is monitored and controlled via converter controller 120. The converted AC power is then transmitted from RSC 112 to the generator rotor via rotor bus 108. In this way, reactive power control of the generator is facilitated by controlling the rotor current and voltage.

[0051] Now for reference 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 aforementioned wind turbine 10) and a total farm-level controller 56. For example, as shown in the illustrated embodiment, the wind farm 50 includes twelve wind turbines, including wind turbine 10. However, in other embodiments, the wind farm 50 may include any other number of wind turbines, such as fewer than twelve 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 via, for example, a wired connection, such as by connecting 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 another embodiment, the field-level controller 56 is configured to send and receive control signals to and from various wind turbines 52, such as allocating active and / or reactive power demands among the wind turbines 52 of the wind farm 50.

[0052] Now for reference Figure 6This diagram illustrates a block diagram of one embodiment of a controller (such as any of the converter controller 120, turbine controller 26, and / or field-level controller 56 described herein) according to exemplary aspects of this disclosure. As shown, the controller may include one or more processors 58, a computer or other suitable processing unit, and associated memory devices(s) 60, which may include suitable computer-readable instructions that, when implemented, configure the controller to perform various functions, such as receiving, sending, and / or performing wind turbine control signals (e.g., performing the methods, steps, calculations, etc., disclosed herein).

[0053] As used herein, the term "processor" refers not only to an integrated circuit known in the art as being contained in a computer, but also to a controller, microcontroller, microcomputer, programmable logic controller (PLC), application-specific integrated circuit (ASIC), and other programmable circuits. Additionally, the memory device(s) 60 may generally include (but are not limited to) 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 discs (MOD), digital versatile discs (DVDs), and / or other suitable memory elements.

[0054] Multiple such memory devices 60 may be generally configured to store suitable computer-readable instructions that, when implemented by the processors 58, configure the controller to perform various functions as described herein. Additionally, the controller may include a communication interface 62 to facilitate communication between the controller and various components of the wind turbine 10. The interface may include one or more circuits, terminals, pins, contacts, conductors, or other components for sending and receiving control signals. Furthermore, the controller may include a sensor interface 64 (e.g., one or more analog-to-digital converters) to allow signals transmitted from sensors 66, 68 to be converted into signals that can be understood and processed by the processors 58.

[0055] Now for reference Figure 7 and Figure 8 The illustration shows a system 200 and a method 250 for providing grid formation control for a doubly-fed generator for a wind turbine, according to the present disclosure. Figure 7 A schematic diagram of one embodiment of the system 200 according to the present disclosure is shown, and in particular a single-line diagram of a doubly fed wind turbine generator 120 having an advanced control structure for grid formation characteristics is shown. Figure 8 The illustration shows a flowchart of one embodiment of a method 250 for providing grid formation control for a doubly-fed generator 120.

[0056] Special reference Figure 7System 200 may include many of the features described herein. Figure 4 The same features, wherein components with the same reference numerals denote the same components. Furthermore, as shown, system 200 may include a control structure for controlling the line-side converter, which is similar to... Figure 1 The control structure shown is illustrated. More specifically, as shown, the line-side converter control structure may include a DC regulator 212 and a line current regulator 214. The DC regulator 212 is configured to generate a line-side current command for the line current regulator 214. The line current regulator 214 then generates a line-side voltage command for the modulator 218. The modulator 218 also receives an output (e.g., a phase-locked loop angle) from a phase-locked loop 216 to generate one or more gate pulses for the line-side converter 114. The phase-locked loop 216 typically uses a voltage feedback signal to generate its output.

[0057] Furthermore, as shown in the figure, system 200 may also include a unique control structure for controlling the grid-side converter 112 using grid formation characteristics. Specifically, as... Figure 8 As shown, system 200 may include a stator voltage regulator 206 for providing this grid formation characteristic. Additionally, as shown, system 200 may include a grid voltage / reactive power volt-ampere regulator 202, an inertial power regulator 204, a rotor current regulator 208, and a modulator 210. (Refer to...) Figures 8 to 11 This allows for a better understanding of such components and their operation.

[0058] More specifically, as will be explained, system 200 includes an inner-loop current regulator structure and a fast stator voltage regulator to translate voltage commands from grid forming control into rotor current regulator commands. Therefore, the systems and methods of this disclosure provide control of the rotor voltage of a doubly-fed wind turbine generator 120 to meet higher-level commands regarding the amplitude and angle of the stator voltage. This control must be relatively fast and insensitive to the current flowing in the stator of the doubly-fed wind turbine generator 120. Therefore, to explain the concept more clearly, in Figure 9 The simplified equivalent circuit of a doubly-fed wind turbine generator 120 is shown. More specifically, as shown in the figure, the simplified circuit neglects grid-side resistance, assumes zero stator leakage, and assumes a unity turns ratio between the rotor and stator. Therefore, the following relationship describes the physical system based on a rotating coordinate system synchronized with the grid connection (VT) via a phase-locked loop (PLL). Variables in italics are complex phase angles or impedances.

[0059] VS = VT + jXT*IT

[0060] IS = IT – IL

[0061] IR = IS + IM

[0062] IM = VS / (j Xm ) = j Bmag *VS

[0063] VR = slip ratio* ( VS + IR*( RR + j XR*Slip

[0064] VS_Cmd_xy = E I *[cos(δ IT ) + j sin(δ IT ) ]= VS_Cmd_x + j VS_Cmd_y

[0065] definition:

[0066] XT = Transformer reactance

[0067] Xmag = Magnetizing reactance

[0068] Bmag = -1 / Xmag

[0069] RR,XR = Rotor resistance and reactance

[0070] Slip = 1 - Rotor speed / Synchronous speed

[0071] E I = Targeting VS higher-level commands for amplitude

[0072] δ IT = Targeting VS Higher-level commands relative to the PLL angle

[0073] Now, especially for reference Figure 8 A flowchart of one embodiment of a method 250 for providing grid forming control for a doubly-fed generator 120 is provided. Generally, method 250 is referred to herein. Figures 2 to 7 The wind turbine 10 is described herein. However, it should be appreciated that the disclosed method 250 can be implemented using a wind turbine with any other suitable construction. Furthermore, although for illustrative and discussion purposes, Figure 8 The steps are described in a specific order, but the methods discussed herein are not limited to any particular order or arrangement. Those skilled in the art will recognize, using the disclosure provided herein, that various steps of the methods disclosed herein may be omitted, rearranged, combined, and / or modified in various ways without departing from the scope of this disclosure.

[0074] As shown in (252), method 250 includes receiving one or more voltage commands via stator voltage regulator 206. Furthermore, in embodiments, the voltage commands(s) may include stator voltage amplitude commands and / or stator voltage angle commands (i.e., Figure 7 (VS_Mag_Cmd and VS_Angle_Cmd). More specifically, in the embodiments, such as Figure 7 As shown, method 250 may include determining (multiple) voltage commands via at least one of voltage / reactive current-voltage regulator 202 or inertial power regulator 204 using one or more reference commands, for example, from an external controller. In an embodiment, the external controller may include, for example, turbine controller 26 of wind turbine 10 or field-level controller 56 of wind farm 50. Thus, as shown, (multiple) reference commands may include at least one of a voltage reference (e.g., VT_Ref) or reactive current-voltage reference from field-level controller 56 and / or a power reference (e.g., Power_Ref) from turbine controller 26.

[0075] Re-reference Figure 8 As shown in (254), method 250 includes determining one or more rotor current commands (e.g., based on magnetization current command 238 and / or stator current feedback signal 240 of doubly-fed generator 120) via stator voltage regulator 206. Figure 7 (IRCmdy and IRCmdx). It should be understood that the stator feedback current 240 is a strong indicator of the characteristics of the externally connected power system (i.e., the power grid). Therefore, the stator feedback current 240 can be used as a feedback signal to decouple the stator voltage response to changes from the characteristics of the power grid.

[0076] More specifically, such as Figure 10 The illustration shows a schematic diagram of one embodiment of an example component of a stator voltage regulator 206. In the illustrated embodiment, the signal is represented in x and y coordinates of the reference terminal voltage phase angle. Complex variable notation is used for clarity. Furthermore, as shown, the stator voltage regulator 206 may include a prediction path 220 and a corrector path 222. Moreover, as shown at the beginning of prediction path 220, the stator voltage regulator 206 is configured to receive a higher-level command (e.g., E) of the stator voltage amplitude. I ) and higher-level commands (e.g., δ) of the stator voltage relative to the phase-locked loop angle. ITFurthermore, continuing along prediction path 220, stator voltage regulator 206 can then convert (multiple) voltage commands into stator voltage commands (e.g., VS_Cmd_xy), as shown at 224. Stator voltage regulator 206 can then determine a magnetizing current feedforward signal (e.g., IM_FF_xy) based on the stator voltage commands and magnetization admittance (e.g., jBmag 226). In one embodiment, for example, magnetization admittance may correspond to magnetization susceptance. Accordingly, the magnetizing current feedforward signal is configured to facilitate a rapid response of the stator voltage to the stator voltage commands.

[0077] Referring specifically to correction path 222, stator voltage regulator 206 can also receive a stator voltage feedback signal (e.g., VS_Fbk_xy) and, as shown at 230, determine the difference between the stator voltage feedback signal and the stator voltage command from prediction path 220. Therefore, in an embodiment, as shown, stator voltage regulator 206 can also determine a magnetizing current correction signal (e.g., IM_Corr_xy) via proportional-integral regulator 232. Thus, as shown at 228 in prediction path 220, stator voltage regulator 206 can then add a magnetizing current feedforward signal to the magnetizing current correction signal to determine a magnetizing current command 238 (e.g., IM_Cmd_xy). In an alternative embodiment, magnetizing current command 238 can be a constant value.

[0078] Furthermore, as shown at 234, the stator voltage regulator 206 can determine (e.g., IM_Cmd_xy) rotor current commands based on the magnetizing current command 238 (e.g., IS_Fbk_xy) and the stator current feedback signal 240 (e.g., IS_Fbk_xy) of the doubly-fed generator 120. For example, in an embodiment, the stator current feedback signal 240 of the doubly-fed generator 120 can be measured. Therefore, in an embodiment, the measured stator current signal 240 of the doubly-fed generator 120 can be fed into the rotor current commands of the doubly-fed generator 120, as shown at 234, to substantially decouple the stator response stator voltage from one or more grid characteristics. More specifically, in a particular embodiment, as shown, the stator voltage regulator 206 can determine (e.g., multiple) rotor current commands 242 by adding the magnetizing current command 238 to the measured stator current feedback signal 240. Furthermore, as shown at 236, limiter 236 can appropriately limit the rotor current command to comply with (a plurality of) equipment ratings.

[0079] Therefore, re-reference Figure 8 As shown at (256), method 250 also includes using one or more rotor current commands to control the rotor voltage of the doubly-fed generator 120 to achieve (multiple) higher-level voltage commands. For example, as Figure 7As shown, the output from stator voltage regulator 206 is a command for the rotor current, which is implemented in rotor current regulator 208 by generating rotor voltage commands (e.g., VRCmdx and VRCmdy) for modulator 210. Modulator 210 also receives a phase-locked loop angle and a reference angle from phase-locked loop 216 to generate one or more gate pulses for rotor-side converter 112.

[0080] Now for reference Figure 11 In some embodiments, method 250 may further include adaptively fine-tuning the magnetization admittance by calculating the effective admittance based on the stator voltage feedback signal and the magnetization current command. More specifically, in embodiments such as Figure 11 As shown, the converter controller 120 can implement a control scheme 300 for calculating the effective admittance (e.g., Bmag). For example, as shown, the control scheme 300 may include determining the absolute value 302 of the magnetizing current command (IM_Cmd_xy). Furthermore, as shown at 304, the control scheme 300 may include inverting the sign of the magnetizing current command to obtain a magnetizing current value 306. Furthermore, as shown at 308, the control scheme 300 may include determining the absolute value of the stator voltage feedback signal (e.g., VS_Fbk_xy). Therefore, as shown at 310, the control scheme 300 may include dividing the magnetizing current value by the absolute value of the stator voltage feedback signal to obtain a quotient value 312. Therefore, as shown at 314, the control scheme 300 may include filtering the quotient value 312 to remove noise and determine the effective admittance Bmag. In such an embodiment, the response of the effective admittance is slower than the response of the magnetizing current correction signal.

[0081] Further aspects of the invention are provided by the subject matter of the following provisions:

[0082] Clause 1. A method for providing grid formation control for a doubly-fed generator of a wind turbine, the method comprising:

[0083] Receive one or more voltage commands via the stator voltage regulator of the converter controller;

[0084] The stator voltage regulator determines one or more rotor current commands based on the magnetizing current command and the stator current feedback signal of the doubly-fed generator; and

[0085] The rotor voltage of the doubly-fed generator is controlled using one or more rotor current commands to achieve the one or more voltage commands.

[0086] Clause 2. The method according to Clause 1, wherein the one or more voltage commands include at least one of a stator voltage amplitude command or a stator voltage angle command.

[0087] Clause 3. The method according to Clause 2 further includes determining the one or more voltage commands via at least one of a voltage regulator, a reactive current-ampere regulator, or an inertial power regulator using one or more reference commands.

[0088] Clause 4. The method according to Clause 3 further includes receiving the one or more reference commands from an external controller, the external controller including at least one of a turbine controller of the wind turbine or a field-level controller of the wind farm, the wind farm including the wind turbine and at least one additional wind turbine.

[0089] Clause 5. The method according to Clause 4, wherein the one or more reference commands include at least one of a voltage reference from the field controller or a power reference from the turbine controller.

[0090] Clause 6. The method described pursuant to any of the preceding clauses further comprises:

[0091] The one or more voltage commands are converted into stator voltage commands via the stator voltage regulator;

[0092] The stator voltage regulator determines a magnetizing current feedforward signal based on the stator voltage command and magnetization admittance, the magnetizing current feedforward signal promoting a rapid response of the stator voltage to the stator voltage command; and

[0093] The magnetizing current feedforward signal is added to the magnetizing current correction signal to determine the magnetizing current command.

[0094] 7. The method described in Clause 6 further includes:

[0095] Receive stator voltage feedback signal;

[0096] Determine the difference between the stator voltage feedback signal and the stator voltage command; and

[0097] The magnetization current correction signal is determined via a proportional-integral regulator.

[0098] Clause 8. The method according to Clause 7 further includes adaptively fine-tuning the magnetization admittance by calculating the effective admittance based on the stator voltage feedback signal and the magnetization current command.

[0099] Clause 9. The method according to Clause 8, wherein calculating the effective admittance based on the stator voltage feedback signal and the magnetizing current command further comprises:

[0100] Determine the absolute value of the magnetizing current command;

[0101] Invert the sign of the magnetization current command to obtain the magnetization current value;

[0102] Determine the absolute value of the stator voltage feedback signal;

[0103] Divide the magnetizing current value by the absolute value of the stator voltage feedback signal to obtain the quotient; and

[0104] The quotient is filtered to remove noise and determine the effective admittance.

[0105] Clause 10. The method according to Clause 9, wherein the response of the effective admittance is slower than the response of the magnetizing current correction signal.

[0106] Clause 11. The method according to Clause 6, wherein determining the one or more rotor current commands based on the magnetizing current command and the stator current feedback signal of the doubly-fed generator further comprises:

[0107] Add the magnetizing current command to the stator current feedback signal.

[0108] Clause 12. The method according to any one of the preceding clauses, wherein controlling the rotor voltage of the doubly-fed generator using the one or more voltage commands further comprises:

[0109] The stator voltage regulator sends commands from one or more rotor current regulators to the rotor current regulator of the converter controller, which provides control of the rotor voltage of the doubly-fed generator via the rotor-side power converter.

[0110] Clause 13. A converter controller for providing grid formation control for a doubly-fed generator of a wind turbine, the converter controller comprising:

[0111] A stator voltage regulator includes at least one processor configured to perform a plurality of operations, the plurality of operations including:

[0112] Receive one or more control commands;

[0113] One or more rotor current commands are determined based on at least one of the magnetizing current command and the stator current feedback signal of the doubly-fed generator; and

[0114] The rotor voltage of the doubly-fed generator is controlled using one or more rotor current commands to achieve the one or more voltage commands.

[0115] Clause 14. The converter controller according to Clause 13, wherein the one or more voltage commands include at least one of a stator voltage amplitude command or a stator voltage angle command.

[0116] Clause 15. The converter controller as described in Clause 14 further includes:

[0117] A voltage / reactive current-voltage regulator for receiving a voltage reference or a reactive current-voltage reference from a field-level controller and determining the stator voltage amplitude command based on at least one of the voltage reference or the reactive current-voltage reference.

[0118] Clause 16. The converter controller according to Clause 14 further includes:

[0119] An inertial power regulator is used to receive a power reference from the turbine controller of the wind turbine and determine the stator voltage amplitude command based on the power reference.

[0120] Clause 17. The converter controller according to Clauses 13 to 16, wherein the plurality of operations further includes:

[0121] Convert the one or more voltage commands into stator voltage commands;

[0122] A magnetizing current feedforward signal is determined based on the stator voltage command and the magnetization admittance, the magnetizing current feedforward signal promoting a rapid response of the stator voltage to the stator voltage command;

[0123] The magnetizing current feedforward signal is added to the magnetizing current correction signal to determine the magnetizing current command;

[0124] Receive stator voltage feedback signal;

[0125] Determine the difference between the stator voltage feedback signal and the stator voltage command; and

[0126] The magnetization current correction signal is determined via a proportional-integral regulator.

[0127] Clause 18. The converter controller according to Clause 17, wherein determining the one or more rotor current commands based on at least one of the magnetizing current command and the stator current feedback signal of the doubly-fed generator further comprises:

[0128] Add the magnetizing current command to the stator current feedback signal.

[0129] Clause 19. The converter controller according to Clauses 13 to 18, wherein controlling the rotor voltage of the doubly-fed generator using the one or more voltage commands further includes:

[0130] The stator voltage regulator sends commands from one or more rotor current regulators to the rotor current regulator of the converter controller, which provides control of the rotor voltage of the doubly-fed generator via the rotor-side power converter.

[0131] Clause 20. A method for providing grid formation control for a doubly-fed generator of a wind turbine, the method comprising:

[0132] Measure the stator current signal of the doubly-fed generator; and

[0133] The stator current signal is fed into the rotor current command of the doubly-fed generator to substantially decouple the stator response stator voltage from one or more grid characteristics; and

[0134] The rotor voltage of the doubly-fed generator is controlled using the rotor current command.

[0135] 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 providing grid formation control of a doubly-fed generator of a wind turbine, the method comprising: receiving one or more voltage commands via a stator voltage regulator of a converter controller; determining one or more rotor current regulator commands from the one or more voltage commands, a magnetizing current command, and a stator current feedback signal of the doubly-fed generator via the stator voltage regulator; and controlling a rotor voltage of the doubly-fed generator using the one or more rotor current regulator commands to achieve the one or more voltage commands, wherein controlling the rotor voltage comprises sending the one or more rotor current regulator commands to a rotor current regulator of the converter controller via the stator voltage regulator, the converter controller providing control of the rotor voltage of the doubly-fed generator via a rotor-side power converter.

2. The method of claim 1, wherein, The one or more voltage commands comprise at least one of a stator voltage magnitude command or a stator voltage angle command.

3. The method of claim 2, further comprising determining the one or more voltage commands using one or more reference commands via at least one of a voltage regulator, a reactive volt-ampere regulator, or an inertial power regulator.

4. The method of claim 3, further comprising receiving the one or more reference commands from an external controller comprising at least one of a turbine controller of the wind turbine or a farm-level controller of a wind farm comprising the wind turbine and at least one additional wind turbine.

5. The method of claim 4, wherein, The one or more reference commands comprise at least one of a voltage reference from the farm-level controller or a power reference from the turbine controller.

6. The method of claim 1, further comprising: converting the one or more voltage commands to a stator voltage command via the stator voltage regulator; determining a magnetizing current feedforward signal from the stator voltage command and a magnetizing admittance via the stator voltage regulator, the magnetizing current feedforward signal facilitating a fast response of a stator voltage to the stator voltage command; and adding the magnetizing current feedforward signal to a magnetizing current correction signal to determine the magnetizing current command.

7. The method of claim 6, further comprising: receiving a stator voltage feedback signal; determining a difference between the stator voltage feedback signal and the stator voltage command; and determining the magnetizing current correction signal via a proportional-integral regulator.

8. The method of claim 7, further comprising fine-tuning the magnetizing admittance adaptively by calculating an effective admittance from the stator voltage feedback signal and the magnetizing current command.

9. The method of claim 8, wherein, Calculating the effective admittance from the stator voltage feedback signal and the magnetizing current command further comprises: determining an absolute value of the magnetizing current command; inverting a sign of the magnetizing current command to obtain a magnetizing current value; determining an absolute value of the stator voltage feedback signal; dividing the magnetizing current value by the absolute value of the stator voltage feedback signal to obtain a quotient value; and filtering the quotient value to remove noise and determine the effective admittance.

10. The method of claim 9, wherein, The effective admittance is slower to respond than the magnetizing current correction signal.

11. The method of claim 6, wherein, Determining the one or more rotor current regulator commands from the magnetizing current command and a stator current feedback signal of the doubly-fed generator further comprises: adding the magnetizing current command to the stator current feedback signal.

12. A converter controller for providing grid formation control of a doubly-fed generator of a wind turbine, the converter controller comprising: a stator voltage regulator comprising at least one processor configured to perform a plurality of operations, the plurality of operations comprising: receiving one or more control commands; determining one or more rotor current regulator commands from the one or more voltage commands and at least one of a magnetizing current command and a stator current feedback signal of the doubly-fed generator; and controlling a rotor voltage of the doubly-fed generator using the one or more rotor current regulator commands to achieve the one or more voltage commands, wherein controlling the rotor voltage comprises sending the one or more rotor current regulator commands to a rotor current regulator of the converter controller via the stator voltage regulator, the converter controller providing control of the rotor voltage of the doubly-fed generator via a rotor-side power converter.

13. The converter controller of claim 12, wherein, The one or more voltage commands comprise at least one of a stator voltage magnitude command or a stator voltage angle command.

14. The converter controller of claim 13, further comprising: a voltage / reactive var regulator to receive a voltage reference or a reactive var reference from a field level controller and determine the stator voltage magnitude command based on at least one of the voltage reference or the reactive var reference.

15. The converter controller of claim 13, further comprising: an inertial power regulator to receive a power reference from a turbine controller of the wind turbine and determine the stator voltage magnitude command based on the power reference.

16. The converter controller of claim 12, wherein, The plurality of operations further comprise: converting the one or more voltage commands to a stator voltage command; determining a magnetizing current feedforward signal from the stator voltage command and a magnetizing admittance, the magnetizing current feedforward signal facilitating a fast response of a stator voltage to the stator voltage command; adding the magnetizing current feedforward signal to a magnetizing current correction signal to determine the magnetizing current command; receiving a stator voltage feedback signal; determining a difference between the stator voltage feedback signal and the stator voltage command; and determining the magnetizing current correction signal via a proportional-integral regulator.

17. The converter controller of claim 16, wherein, Determining the one or more rotor current regulator commands from the magnetizing current command and a stator current feedback signal of the doubly-fed generator further comprises: adding the magnetizing current command to the stator current feedback signal.

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