System and method for providing blackstart of grid-forming inverter-based resources

Abstract

A method of blackstarting a power generating farm having a plurality of inverter-based resources includes satisfying one or more blackstarting preconditions. Upon satisfaction of the one or more blackstarting preconditions, the method includes implementing a self-excitation process for a first inverter-based resource of the plurality of inverter-based resources. The self-excitation process includes utilizing at least one of a DC link capacitor or a first converter of a power conversion assembly of the first inverter-based resource. The self-excitation process further includes self-exciting a generator of the first inverter-based resource of the plurality of inverter-based resources by ramping up a DC bus setpoint of a DC link of the first inverter-based resource to gradually increase terminal voltage of the generator and voltage of the DC link in a controlled manner. Further, the method includes blackstarting remaining inverter-based resources of the plurality of inverter-based resources using the self-excited first inverter-based resource.

Description

FIELD

[0001] The present disclosure relates generally to inverter-based resources and, more particularly, to systems and methods for providing blackstart of grid-forming inverter-based resources. BACKGROUND

[0002] Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is typically geared to a generator for producing electricity.

[0003] Wind turbines can be distinguished in two types: fixed speed and variable speed turbines. Conventionally, variable speed wind turbines are controlled as current sources connected to a power grid. In other words, the variable speed wind turbines rely on a grid frequency detected by a phase locked loop (PLL) as a reference and inject a specified amount of current into the grid. The conventional current source control of the wind turbines is based on the assumptions that the grid voltage waveforms are fundamental voltage waveforms with fixed frequency and magnitude and that the penetration of wind power into the grid is low enough so as to not cause disturbances to the grid voltage magnitude and frequency. Thus, the wind turbines simply inject the specified current into the grid based on the fundamental voltage waveforms. However, with the rapid growth of the wind power, wind power penetration into some grids has increased to the point where wind turbine generators have a significant impact on the grid voltage and frequency. When wind turbines are located in a weak grid, wind turbine power fluctuations may lead to an increase in magnitude and frequency variations in the grid voltage. These fluctuations may adversely affect the performance and stability of the PLL and wind turbine current control and adversely affect the performance of loads connected to the network.

[0004] Furthermore, many existing renewable generation converters, such as doubly fed wind turbine generators, operate in a “grid-following” mode. Gridfollowing type devices utilize fast current-regulation loops to control active and reactive power exchanged with the grid. More specifically, FIG. 1 illustrates the basic elements of the main circuit and converter control structure for a grid-following doubly fed wind turbine generator. As shown, the active power reference to the converter is developed by the energy source regulator, e.g., the turbine control portion of a wind turbine. This is conveyed as a torque reference which represents the lesser of the maximum attainable power from the energy source at that instant, or a curtailment command from a higher-level grid controller. The converter control then determines a current reference for the active component of current to achieve the desired torque. Accordingly, the doubly fed wind turbine generator includes functions that manage the voltage and reactive power in a manner that results in a command for the reactive component of current. Wide-bandwidth current regulators then develop commands for voltage to be applied by the converters to the system, such that the actual currents closely track the commands.

[0005] Alternatively, grid-forming type converters provide a voltage-source characteristic, where the angle and magnitude of the voltage are controlled to achieve the regulation functions needed by the grid. With this structure, current will flow according to the demands of the grid while the converter contributes to establishing a voltage and frequency for the grid. This characteristic is comparable to conventional generators based on a turbine driving a synchronous machine. Thus, a grid-forming source must include the following basic functions: (1) support grid voltage and frequency for any current flow within the rating of the equipment, both real and reactive; (2) prevent operation beyond equipment voltage or current capability by allowing grid voltage or frequency to change rather than disconnecting equipment (disconnection is allowed only when voltage or frequency are outside of bounds established by the grid entity); (3) remain stable for any grid configuration or load characteristic, including serving an isolated load or connected with other grid-forming sources, and switching between such configurations; (4) share total load of the grid among other grid-forming sources connected to the grid; (5) ride through grid disturbances, both major and minor, and (6) meet requirements (1)-(5) without requiring fast communication with other control systems existing in the grid, or externally-created logic signals related to grid configuration changes.

[0006] The basic control structure to achieve the above grid-forming objectives was developed and field-proven for battery systems in the early 1990’s (see e.g., United States Patent No.: 5,798,633 entitled “Battery Energy Storage Power Conditioning System”). Applications to full-converter wind generators and solar generators are disclosed in United States Publication No.: 2010 / 0142237 entitled “System and Method for Control of a Grid Connected Power Generating System,” and United States Patent No.: 9,270,194 entitled “Controller for controlling a power converter.” However, such implementations have been employed on full-converter wind generators.

[0007] Blackstart capability of a conventional generator is an important element in grid restoration following a blackout. With inverter-based resources displacing many synchronous generators in the grid, there is an emerging grid requirement for inverter-based resources to provide blackstart capability similar to conventional generators. Grid forming inverter-based resources can be capable of providing blackstart.

[0008] In view of the foregoing, the present disclosure is directed to systems and methods for providing blackstart of grid-forming inverter-based resources. BRIEF DESCRIPTION

[0009] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0010] In an aspect, the present disclosure is directed to a method of blackstarting a power generating farm having a plurality of inverter-based resources. The method includes satisfying one or more blackstarting preconditions. Upon satisfaction of the one or more blackstarting preconditions, the method includes implementing a self excitation process for a first inverter-based resource of the plurality of inverter-based resources. The self-excitation process includes utilizing at least one of a DC link capacitor or a first converter of a power conversion assembly of the first inverterbased resource. The self-excitation process further includes self-exciting a generator of the first inverter-based resource of the plurality of inverter-based resources by ramping up a DC bus setpoint of a DC link of the first inverter-based resource to gradually increase terminal voltage of the generator and voltage of the DC link in a controlled manner. Further, the method includes blackstarting remaining inverterbased resources of the plurality of inverter-based resources using the self-excited first inverter-based resource.

[0011] In another aspect, the present disclosure is directed to a wind farm. The wind farm includes a plurality of wind turbines comprising, at least, a first wind turbine. The first wind turbine has a generator electrically coupled to a power conversion assembly. The power conversion assembly has a line-side converter and a rotor-side converter coupled together via a DC link, the DC link comprising a DC link capacitor. The wind farm further includes a controller having at least one processor configured to perform a plurality of operations. The plurality of operations include satisfying one or more blackstarting preconditions, and upon satisfaction of the one or more blackstarting preconditions, implementing a self-excitation process for the first wind turbine. The self-excitation process includes utilizing at least one of the DC link capacitor or the first converter of the power conversion assembly and self-exciting the generator by ramping up a DC bus setpoint of a DC link of the first inverter-based resource to gradually increase terminal voltage of the generator and voltage of the DC link in a controlled manner. The method also includes blackstarting remaining wind turbines of the plurality of wind turbines using the self-excited first wind turbine.

[0012] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

[0014] FIG. 1 illustrates a one-line diagram of a doubly fed wind turbine generator with structure of converter controls for grid-following application according to conventional construction;

[0015] FIG. 2 illustrates a perspective view of one embodiment of a wind turbine according to the present disclosure;

[0016] FIG. 3 illustrates a simplified, internal view of one embodiment of a nacelle according to the present disclosure;

[0017] FIG. 4 illustrates a schematic view of one embodiment of a wind turbine electrical power system suitable for use with the wind turbine shown in FIG. 1;

[0018] FIG. 5 illustrates a schematic view of one embodiment of a wind farm having a plurality of wind turbines according to the present disclosure;

[0019] FIG. 6 illustrates a block diagram of one embodiment of a controller according to the present disclosure;

[0020] FIG. 7 illustrates a one-line diagram of a doubly fed wind turbine generator with converter controls for grid-forming application according to the present disclosure;

[0021] FIG. 8 illustrates a schematic diagram of an embodiment of an inverterbased resource of a power generating farm, such as wind farm, having blackstart capability according to the present disclosure;

[0022] FIG. 9 illustrates a schematic diagram of an embodiment of a power generating farm, such as wind farm, having blackstart capability according to the present disclosure; and

[0023] FIG. 10 illustrates a flow diagram of an embodiment of a method of blackstarting a power generating farm having a plurality of inverter-based resources and a power generating device according to the present disclosure. DETAILED DESCRIPTION

[0024] Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0025] Blackstarting a doubly-fed-induction-generator-based wind turbine requires an external power supply in the form of additional battery storage or a diesel generator to generate three phase AC voltage at the turbine terminal. Using this voltage, the wind turbine can be blackstarted in the absence of the grid. However, it would also be advantageous to provide blackstarting capability to DFIG-based wind turbines without requiring an external power supply.

[0026] Accordingly, the present disclosure is generally directed to systems and methods for blackstarting a power generating farm, having plurality of inverter-based resources, such as wind turbines. In particular, in an embodiment, the present disclosure is directed to method whereby a generator of a first wind turbine is started without any external power generating source and from zero terminal voltage, given the auxiliary systems, pitch system, and yaw system are powered by existing backup at the beginning of the restart process. In particular embodiments, the generator may be a doubly fed induction generator (DFIG). Thus, in an embodiment, the method uses a self-excitation process of an induction machine to gradually buildup the terminal voltage in a controlled manner. In an embodiment, and as a precondition, the drivetrain of the wind turbine should be rotating at more than cut-in speed and there should either be some terminal voltage generated due to residual magnetism, or a DC link capacitor of the wind turbine should have some pre-charge. Moreover, in an embodiment, the method may be used along with grid forming control to establish terminal voltage and frequency at rated voltage and frequency. Using the generated voltage of the first wind turbine, additional wind turbines of the wind farm can then be blackstarted.

[0027] Referring now to the drawings, FIG. 2 illustrates a perspective view of an embodiment of a wind turbine 10 according to the present disclosure. The wind turbine 10 described herein may be an onshore wind turbine, as shown in FIG. 2 or an offshore wind turbine. Further, as shown in FIG. 2, 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 outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in an alternative embodiment, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub 20 may be rotatably coupled to an electric generator 24 (FIG. 3) positioned within the nacelle 16 to permit electrical energy to be produced.

[0028] 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. Further, the controller 26 may be communicatively coupled to any number of the components of the wind turbine 10 in order to control the operation of such components and / or implement a corrective or control action. As such, the controller 26 may include a computer or other suitable processing unit. Thus, in several embodiments, the controller 26 may include suitable computer-readable instructions that, when implemented, configure the controller 26 to perform various different functions, such as receiving, transmitting and / or executing wind turbine control signals. Accordingly, the controller 26 may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences), de-rating or up-rating the wind turbine, and / or individual components of the wind turbine 10.

[0029] Referring now to FIG. 2, a simplified, internal view of one embodiment of the nacelle 16 of the wind turbine 10 shown in FIG. 1 is illustrated. As shown, a generator 24 may be disposed within the nacelle 16 and supported atop a bedplate 46. In general, the generator 24 may be coupled to the rotor 18 for producing electrical power from the rotational energy generated by the rotor 18. For example, as shown in the illustrated embodiment, the rotor 18 may include a rotor shaft 34 coupled to the hub 20 for rotation therewith. The rotor shaft 34 may, in turn, be rotatably coupled to a generator shaft 36 of the generator 24 through a gearbox 38. As is generally understood, 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 to a high speed, low torque output to drive the generator shaft 36 and, thus, the generator 24.

[0030] The wind turbine 10 may also one or more pitch drive mechanisms 32 communicatively coupled to the wind turbine controller 26, with each pitch adjustment mechanism(s) 32 being configured to rotate a pitch bearing 40 and thus the individual rotor blade(s) 22 about its respective pitch axis 28. In addition, as shown, the wind turbine 10 may include one or more yaw drive mechanisms 42 configured to change the angle of the nacelle 16 relative to the wind (e.g., by engaging a yaw bearing 44 of the wind turbine 10 that is arranged between the nacelle 16 and the tower 12 of the wind turbine 10).

[0031] In addition, the wind turbine 10 may also include one or more sensors 66, 68 for monitoring various wind conditions of the wind turbine 10. For example, the incoming wind direction 52, wind speed, or any other suitable wind condition near of the wind turbine 10 may be measured, such as through use of a suitable weather sensor 66. Suitable weather sensors may include, for example, light detection and ranging devices, sonic detection and ranging devices, anemometers, wind vanes, barometers, radio detection and ranging devices or any other sensing device which can provide wind directional information now known or later developed in the art. Further sensors 68 may be utilized to measure additional operating parameters of the wind turbine 10, such as voltage, current, vibration, etc. as described herein.

[0032] Referring now to FIG. 4, a schematic diagram of one embodiment of a wind turbine power system 100 is illustrated in accordance with aspects of the present disclosure. Although the present disclosure will generally be described herein with reference to the system 100 shown in FIG. 4, those of ordinary skill in the art, using the disclosures provided herein, should understand that aspects of the present disclosure may also be applicable in other power generation systems, and, as mentioned above, that the invention is not limited to wind turbine systems.

[0033] In the embodiment of FIG. 4 and as mentioned, the rotor 18 of the wind turbine 10 (FIG. 2) may, optionally, be coupled to the gearbox 38, which is, in turn, coupled to a generator 102, which may be a doubly fed induction generator (DFIG). As shown, the generator 102 may be connected to a stator bus 104. Further, as shown, a power conversion assembly 106 may be connected to the generator 102 via a rotor bus 108, and to the stator bus 104 via a line side bus 110. As such, the stator bus 104 may provide an output multiphase power (e.g., three-phase power) from a stator of the generator 102, and the rotor bus 108 may provide an output multiphase power (e.g., three-phase power) from a rotor of the generator 102. The power conversion assembly 106 may also include a rotor-side converter (RSC) 112 and a line-side converter (LSC) 114. The generator 102 is coupled via the rotor bus 108 to the rotorside converter 112. Additionally, the RSC 112 is coupled to the LSC 114 via a DC link 116 across which is a DC link capacitor 118. The LSC 114 is, in turn, coupled to the line side bus 110.

[0034] The RSC 112 and the LSC 114 may be configured for normal operating mode in a three-phase, pulse width modulation (PWM) arrangement using one or more switching devices, such as insulated gate bipolar transistor (IGBT) switching elements. In addition, the power conversion assembly 106 may be coupled to a converter controller 120 in order to control the operation of the rotor-side converter 112 and / or the line-side converter 114 as described herein. It should be noted that the converter controller 120 may be configured as an interface between the power conversion assembly 106 and the turbine controller 26 and may include any number of control devices.

[0035] In typical configurations, various line contactors and circuit breakers including, for example, a grid breaker 122 may also be included for isolating the various components as necessary for normal operation of the generator 102 during connection to and disconnection from a load, such as the electrical grid 124. For example, a system circuit breaker 126 may couple a system bus 128 to a transformer 130, which may be coupled to the electrical grid 124 via the grid breaker 122. In alternative embodiments, fuses may replace some or all of the circuit breakers.

[0036] In operation, alternating current power generated at the generator 102 by rotating the rotor 18 is provided to the electrical grid 124 via dual paths defined by the stator bus 104 and the rotor bus 108. On the rotor bus side 108, sinusoidal multiphase (e.g., three-phase) alternating current (AC) power is provided to the power conversion assembly 106. The rotor-side converter 112 converts the AC power provided from the rotor bus 108 into direct current (DC) power and provides the DC power to the DC link 116. As is generally understood, switching elements (e.g., IGBTs) used in the bridge circuits of the rotor-side converter 112 may be modulated to convert the AC power provided from the rotor bus 108 into DC power suitable for the DC link 116.

[0037] In addition, the line-side converter 114 converts the DC power on the DC link 116 into AC output power suitable for the electrical grid 124. In particular, switching elements (e.g., IGBTs) used in bridge circuits of the line-side 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 conversion assembly 106 can be combined with the power from the stator of the generator 102 to provide multi-phase power (e.g., three-phase power) having a frequency maintained substantially at the frequency of the electrical grid 124 (e.g., 50 Hz or 60 Hz).

[0038] Additionally, various circuit breakers and switches, such as grid breaker 122, system circuit breaker 126, stator sync switch 132, converter 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 current flow is excessive and may damage components of the wind turbine power system 100 or for other operational considerations. Additional protection components may also be included in the wind turbine power system 100.

[0039] Moreover, the power conversion assembly 106 may receive control signals from, for instance, the local control system 176 via the converter controller 120. The control signals may be based, among other things, on sensed states or operating characteristics of the wind turbine power system 100. Typically, the control signals provide control of the operation of the power conversion assembly 106. For example, feedback in the form of a sensed speed of the generator 102 may be used to control the conversion of the output power from the rotor bus 108 to maintain a proper and balanced multi-phase (e.g., three-phase) power supply. Other feedback from other sensors may also be used by the controller(s) 120, 26 to control the power conversion assembly 106, including, for example, stator and rotor bus voltages and current feedbacks. Using the various forms of feedback information, switching control signals (e.g., gate timing commands for IGBTs), stator synchronizing control signals, and circuit breaker signals may be generated.

[0040] The power conversion assembly 106 also compensates or adjusts the frequency of the three-phase power from the rotor for changes, for example, in the wind speed at the hub 20 and the rotor blades 22. Therefore, mechanical and electrical rotor frequencies are decoupled, and the electrical stator and rotor frequency matching is facilitated substantially independently of the mechanical rotor speed.

[0041] Under some states, the bi-directional characteristics of the power conversion assembly 106, and specifically, the bi-directional characteristics of the LSC 114 and RSC 112, facilitate feeding back at least some of the generated electrical power into generator rotor. More specifically, electrical power may be transmitted from the stator bus 104 to the line side bus 110 and subsequently through the line contactor 136 and into the power conversion assembly 106, specifically the LSC 114 which acts as a rectifier and rectifies the sinusoidal, three-phase AC power to DC power. The DC power is transmitted into the DC link 116. The capacitor 118 facilitates mitigating DC link voltage amplitude variations by facilitating mitigation of a DC ripple sometimes associated with three-phase AC rectification.

[0042] The DC power is subsequently transmitted to the RSC 112 that converts the DC electrical power to a three-phase, sinusoidal AC electrical power by adjusting voltages, currents, and frequencies. This conversion is monitored and controlled via the converter controller 120. The converted AC power is transmitted from the RSC 112 via the rotor bus 108 to the generator rotor. In this manner, generator reactive power control is facilitated by controlling rotor current and voltage.

[0043] Referring now to FIG. 5, the wind turbine power system 100 described herein may be part of a wind farm 50. As shown, the wind farm 50 may include a plurality of wind turbines 52, including the wind turbine 10 described above, and an overall farm-level controller 56. For example, as shown in the illustrated embodiment, the wind farm 50 includes twelve wind turbines, including wind turbine 10. However, in other embodiments, the wind farm 50 may include any other number of wind turbines, such as less than twelve wind turbines or greater 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, e.g., through a wired connection, such as by connecting the turbine controller 26 through suitable communicative links 54 (e.g., a suitable cable). Alternatively, the turbine controllers may be communicatively coupled to the farm-level controller 56 through a wireless connection, such as by using any suitable wireless communications protocol known in the art. In further embodiments, the farm-level controller 56 is configured to send and receive control signals to and from the various wind turbines 52, such as for example, distributing real and / or reactive power demands across the wind turbines 52 of the wind farm 50.

[0044] Referring now to FIG. 6, a block diagram of one embodiment of suitable components that may be included within the controller (such as any one of the converter controller 120, the turbine controller 26, and / or the farm-level controller 56 described herein) in accordance with example aspects of the present disclosure is illustrated. As shown, the controller may include one or more processor(s) 58, computer, or other suitable processing unit and associated memory device(s) 60 that may include suitable computer-readable instructions that, when implemented, configure the controller to perform various different functions, such as receiving, transmitting and / or executing wind turbine control signals (e.g., performing the methods, steps, calculations, and the like disclosed herein).

[0045] As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) 60 may generally comprise memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and / or other suitable memory elements.

[0046] Such memory device(s) 60 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 58, configure the controller to perform various functions as described herein. Additionally, the controller may also include a communications interface 62 to facilitate communications between the controller and the various components of the wind turbine 10. An interface can include one or more circuits, terminals, pins, contacts, conductors, or other components for sending and receiving control signals. Moreover, the controller may include a sensor interface 64 (e.g., one or more analog-to-digital converters) to permit signals transmitted from the sensors 66, 68 to be converted into signals that can be understood and processed by the processor(s) 58.

[0047] Referring now to FIG. 7, a schematic diagram of an embodiment of a grid forming power system 200 according to the present disclosure, particularly illustrating a one-line diagram of the doubly fed wind turbine generator 102 with a high-level control structure for grid-forming characteristics. In particular, as shown, the grid forming power system 200 may include many of the same features of FIG. 4 described herein, with components having the same reference characters representing like components. Further, as shown, the grid forming power system 200 may include a control structure for controlling the line-side converter that is similar to the control structure shown in FIG. 1. More particularly, 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 line-side current commands for the line current regulator 214. The line current regulator 214 then generates line-side voltage commands for a 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 generates its output using a voltage feedback signal.

[0048] Furthermore, as shown, the grid forming power system 200 may also include a unique control structure for controlling the rotor-side converter 112 using grid-forming characteristics. In particular, as shown in FIG. 7, the grid forming power system 200 may include a stator voltage regulator 206 for providing such gridforming characteristics. In addition, as shown, the grid forming power system 200 may include a grid voltage / VAR regulator 202, an inertial power regulator 204, a rotor current regulator 208, and a modulator 210.

[0049] Referring now to FIGS. 8-10, the present disclosure is directed to a power generating farm 300 (such as wind farm 50) and method 400 of blackstarting the power generating farm 300 according to the present disclosure. In particular, FIG. 8 illustrates a schematic diagram of an embodiment of a first inverter-based resource 302, such as a wind turbine, that is part of the power generating farm 300 according to the present disclosure. FIG. 9 illustrates a schematic diagram of an embodiment of the inverter-based resource 302 of FIG. 8 providing a constant voltage and frequency to the power generating farm 300 to start up the power generating farm 300 in the absence of grid power according to the present disclosure. FIG. 10 illustrates a flow diagram of an embodiment of the method 400 of blackstarting the power generating farm 300 according to the present disclosure.

[0050] Referring particularly to FIG. 8, in an embodiment, the first inverter-based resource 302 is configured similar to the grid forming power system 200 (i.e., a grid forming wind turbine) illustrated in FIG. 7. Thus, as shown in the illustrated embodiment and previously explained, the grid forming power system 200 includes the wind turbine 10 having capability for connecting to an electrical grid 304. Moreover, as shown, the first inverter-based resource 302 includes a power conversion assembly 306 having a first converter 308 and a second converter 310. In particular, as shown, the first converter 308 is the line-side converter 114 and the second converter 310 is the rotor-side converter 112, which are coupled together via the DC link 116. Furthermore, as shown, the DC link 116 includes a DC link capacitor 118. In addition, as shown, the wind turbine 10 includes the generator 102.

[0051] Furthermore, as shown in FIG. 8, the first inverter-based resource 302 has grid forming capability as illustrated by grid forming (GFM) control module 312 that is communicatively and electrically coupled to the rotor-side converter 112. Moreover, as shown, the first inverter-based resource 302 may include a DC voltage build-up module 314 for providing line side control to the line-side converter 114. More specifically, in an embodiment, as shown, the DC voltage build-up module 314 may include a DC voltage regulator, a flux regulator, a line current regulator, and a modulator. In addition, the first inverter-based resource 302 may include various switches, such as a synchronization switch 316, a load switch 318 for coupling a load 320 to the stator bus 104, and a grid breaker 324 for selectively coupling the wind turbine 10 to the grid 304.

[0052] Referring particularly to FIG. 10, the method 400 is described herein with reference to the wind turbine 10 and the wind farm 50 of FIGS. 2-9. However, it should be appreciated that the disclosed method 400 may be implemented with any inverter-based resources in addition to wind turbines having any other suitable configurations. In addition, although FIG. 10 depicts steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods disclosed herein can be omitted, rearranged, combined, and / or adapted in various ways without deviating from the scope of the present disclosure.

[0053] As shown at (402), the method 400 includes satisfying one or more blackstarting preconditions. For example, in an embodiment, the blackstarting precondition(s) may include powering one or more auxiliary systems of the wind turbine using an existing backup power system of the wind turbine. In such embodiments, the auxiliary system(s) may include, for example, a control system (e.g., turbine controller 26), a pitch system (e.g., pitch drive mechanism 32), and / or a yaw system (e.g., yaw drive mechanism 44) of the wind turbine 10.

[0054] In further embodiments, the blackstarting precondition(s) may include the grid breaker 324 being open, a rotor circuit being shorted, the generator 102 rotating at a speed greater than or equal to a cut in speed, and / or at least one of a voltage value in a stator terminal of the generator 102 being greater than 0.1 pu due to residual magnetism or the DC link 116 of the first inverter-based resource 302 having a precharge of at least 0.1 pu. More specifically, in an embodiment, the blackstarting precondition(s) may include each of the grid breaker 324 being open, the rotor circuit being shorted, the generator 102 rotating at the speed greater than or equal to the cut in speed, and one of the voltage value in the stator terminal of the generator 102 being greater than 0.1 pu due to residual magnetism or the pre-charge in the DC link 116 of the first inverter-based resource 302 being at least 0.1 pu.

[0055] Upon satisfaction of the one or more blackstarting preconditions, as shown at (404) of FIG. 10, the method 400 includes implementing a self-excitation process for the first inverter-based resource 302 of the plurality of inverter-based resources. For example, in an embodiment, the method 400 may include closing the synchronization switch 322 between the electrical grid 304 and the generator 102 after satisfying the blackstarting precondition(s) to excite a stator of the generator 102. In an embodiment, as shown in FIGS. 8 and 9, the first inverter-based resource 302 is under grid forming control.

[0056] Referring back to FIG. 10, as shown at (406), the self-excitation process includes utilizing at least one of the DC link capacitor 118 of the DC link 116 or the first converter 308 of the power conversion assembly 306 of the first inverter-based resource 302 to self-excite the first inverter-based resource. For example, as shown at (408), the method 400 may include self-exciting the generator 102 of the first inverter-based resource 302 of the plurality of inverter-based resources by ramping up a DC bus setpoint of the DC link 116 of the first inverter-based resource 302 to gradually increase terminal voltage of the generator 102 and a bus voltage of the DC link 116 in a controlled manner. More specifically, in an embodiment, as shown in FIG. 8, the DC voltage build up module 314 is configured to build up the DC bus voltage by ramping up the DC bus setpoint and a flux setpoint to rated voltage / flux with the rotor circuit (e.g., the rotor crowbar) shorted. At this point in the selfexcitation process, the stator terminal voltage and frequency are not at rated voltage / frequency. Furthermore, in an embodiment, the method 400 may include opening the rotor circuit (e.g., containing the GFM control module 312) after gradually increasing the terminal voltage of the DC link 116 of the first inverter-based resource 302 such that grid forming control is enabled.

[0057] In particular embodiments, as an example and as shown at (410), providing the constant voltage and frequency to the remaining inverter-based resources via the first inverter-based resource 302 may include starting the second converter 310 of the power conversion assembly 306 once the bus voltage of the DC link 116 reaches rated voltage to establish a rated terminal voltage at a rated frequency using the grid forming control and disabling flux regulation by the first converter 308. Furthermore, as shown at (412), the method 400 includes blackstarting remaining inverter-based resources of the plurality of inverter-based resources using the self-excited first inverter-based resource 302. More specifically, in an embodiment, as shown in FIG. 9, the remaining inverter-based resources 330 of the power generating farm 300 (e.g., which may be GFM or gird following GFL wind turbines) may be blackstarted by providing a constant voltage and frequency to the remaining inverter-based resources via the first inverter-based resource 302. Accordingly, in an embodiment, the blackstarting process of the present disclosure can be completed without an additional external power generating source, such as an additional anchor generator.

[0058] Further aspects of the invention are provided by the subject matter of the following clauses:

[0059] A method of blackstarting a power generating farm having a plurality of inverter-based resources, the method comprising: satisfying one or more blackstarting preconditions; upon satisfaction of the one or more blackstarting preconditions, implementing a self-excitation process for a first inverter-based resource of the plurality of inverter-based resources, the self-excitation process comprising: utilizing at least one of a DC link capacitor or a first converter of a power conversion assembly of the first inverter-based resource; and self-exciting a generator of the first inverterbased resource of the plurality of inverter-based resources by ramping up a DC bus setpoint of a DC link of the first inverter-based resource to gradually increase terminal voltage of the generator and a bus voltage of the DC link in a controlled manner; and blackstarting remaining inverter-based resources of the plurality of inverter-based resources using the self-excited first inverter-based resource.

[0060] The method of any preceding clause, wherein the first inverter-based resource of the plurality of inverter-based resources is under grid forming control.

[0061] The method of any preceding clause, wherein blackstarting the remaining inverter-based resources of the plurality of inverter-based resources using the terminal voltage further comprises: providing a constant voltage and frequency to the remaining inverter-based resources of the plurality of inverter-based resources via the first inverter-based resource.

[0062] The method of any preceding clause, wherein providing the constant voltage and frequency to the remaining inverter-based resources of the plurality of inverter-based resources via the first inverter-based resource further comprises: starting a second converter of the power conversion assembly once the bus voltage of the DC link reaches rated voltage to establish a rated terminal voltage at a rated frequency using the grid forming control and disabling flux regulation by the first converter.

[0063] The method of any preceding clause, wherein the first inverter-based resource is a wind turbine, and wherein the first converter is a line-side converter and the second converter is a rotor-side converter of the power conversion assembly.

[0064] The method of any preceding clause, wherein the one or more blackstarting preconditions comprises powering one or more auxiliary systems of the wind turbine using an existing backup power system of the wind turbine.

[0065] The method of any preceding clause, wherein the one or more auxiliary systems comprises at least one of a control system, a pitch system, and a yaw system.

[0066] The method of any preceding clause, wherein the one or more blackstarting preconditions comprises at least one of a grid breaker being open, a rotor circuit being shorted, the generator rotating at a speed greater than or equal to a cut in speed, or at least one of a voltage value in a stator terminal of the generator being greater than 0.1 pu due to residual magnetism or a DC link of the first inverter-based resource having a pre-charge of at least 0.1 pu.

[0067] The method of any preceding clause, wherein the one or more blackstarting preconditions comprises each of the grid breaker being open, the rotor circuit being shorted, the generator rotating at the speed greater than or equal to the cut in speed, and one of the voltage value in the stator terminal of the generator is greater than 0.1 pu due to residual magnetism or the pre-charge in the DC link of the first inverter-based resource is at least 0.1 pu.

[0068] The method of any preceding clause, further comprising opening a short of the rotor circuit after gradually increasing the terminal voltage of the generator and the bus voltage of the DC link of the first inverter-based resource to enable the grid forming control.

[0069] The method of any preceding clause, wherein the self-excitation process further comprises closing a synchronization switch of the first inverter-based resource after satisfying the one or more blackstarting preconditions to excite a stator of the generator.

[0070] The method of any preceding clause, wherein the blackstarting is completed without an additional external power generating source.

[0071] The method of any preceding clause, wherein the generator is a doubly fed induction generator.

[0072] A wind farm, comprising: a plurality of wind turbines comprising, at least, a first wind turbine, the first wind turbine comprising a generator electrically coupled to a power conversion assembly, the power conversion assembly comprising a lineside converter and a rotor-side converter coupled together via a DC link, the DC link comprising a DC link capacitor; a controller comprising at least one processor, the at least one processor configured to perform a plurality of operations, the plurality of operations comprising: satisfying one or more blackstarting preconditions; upon satisfaction of the one or more blackstarting preconditions, implementing a selfexcitation process for the first wind turbine, the self-excitation process comprising: utilizing at least one of the DC link capacitor or the first converter of the power conversion assembly; and self-exciting the generator by ramping up a DC bus setpoint of a DC link of the first inverter-based resource to gradually increase terminal voltage of the generator and a bus voltage of a DC link of the first wind turbine in a controlled manner; and blackstarting remaining wind turbines of the plurality of wind turbines using the self-excited first wind turbine.

[0073] The wind farm of any preceding clause, wherein the first wind turbine of the plurality of wind turbines is under grid forming control.

[0074] The wind farm of any preceding clause, wherein blackstarting the remaining wind turbines of the plurality of wind turbines using the terminal voltage further comprises: providing a constant voltage and frequency to the remaining wind turbines of the plurality of wind turbines via the first wind turbine.

[0075] The wind farm of any preceding clause, wherein providing the constant voltage and frequency to the remaining wind turbines of the plurality of wind turbines via the first wind turbine further comprises: starting a second converter of the power conversion assembly once the bus voltage of the DC link reaches rated voltage to establish a rated terminal voltage at a rated frequency using the grid forming control and disabling flux regulation by the first converter.

[0076] The wind farm of any preceding clause, wherein the one or more blackstarting preconditions comprises powering one or more auxiliary systems of the first wind turbine using an existing backup power system of the first wind turbine, wherein the one or more auxiliary systems comprises at least one of a control system, a pitch system, and a yaw system.

[0077] The wind farm of any preceding clause, wherein the one or more blackstarting preconditions comprises at least one of a grid breaker being open, a rotor circuit being shorted, the generator rotating at a speed greater than or equal to a cut in speed, or at least one of a voltage value in a stator terminal of the generator being greater than 0.1 pu due to residual magnetism or a DC link of the first wind turbine having a pre-charge of at least 0.1 pu.

[0078] The wind farm of any preceding clause, wherein the plurality of operations further comprises: closing a synchronization switch of the first wind turbine after satisfying the one or more blackstarting preconditions to excite a stator of the generator; and opening a short of the rotor circuit after gradually increasing the terminal voltage of the generator and the bus voltage of the DC link of the first wind turbine.

[0079] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

1. A method of blackstarting a power generating farm having a plurality of inverter-based resources, the method comprising:satisfying one or more blackstarting preconditions;upon satisfaction of the one or more blackstarting preconditions, implementing a self-excitation process for a first inverter-based resource of the plurality of inverterbased resources, the self-excitation process comprising:utilizing at least one of a DC link capacitor or a first converter of a power conversion assembly of the first inverter-based resource; and self-exciting a generator of the first inverter-based resource of the plurality of inverter-based resources by ramping up a DC bus setpoint of a DC link of the first inverter-based resource to gradually increase terminal voltage of the generator and a bus voltage of the DC link in a controlled manner; and blackstarting remaining inverter-based resources of the plurality of inverterbased resources using the self-excited first inverter-based resource.

2. The method of claim 1, wherein the first inverter-based resource of the plurality of inverter-based resources is under grid forming control.

3. The method of claim 2, wherein blackstarting the remaining inverterbased resources of the plurality of inverter-based resources using the terminal voltage further comprises:providing a constant voltage and frequency to the remaining inverter-based resources of the plurality of inverter-based resources via the first inverter-based resource.

4. The method of claim 3, wherein providing the constant voltage and frequency to the remaining inverter-based resources of the plurality of inverter-based resources via the first inverter-based resource further comprises:starting a second converter of the power conversion assembly once the bus voltage of the DC link reaches rated voltage to establish a rated terminal voltage at a rated frequency using the grid forming control and disabling flux regulation by the first converter.

5. The method of claim 4, wherein the first inverter-based resource is awind turbine, and wherein the first converter is a line-side converter and the second converter is a rotor-side converter of the power conversion assembly.

6. The method of any of the preceding claims, wherein the one or more blackstarting preconditions comprises powering one or more auxiliary systems of the wind turbine using an existing backup power system of the wind turbine.

7. The method of claim 6, wherein the one or more auxiliary systemscomprises at least one of a control system, a pitch system, and a yaw system.

8. The method of any of the preceding claims, wherein the one or more blackstarting preconditions comprises at least one of a grid breaker being open, a rotor circuit being shorted, the generator rotating at a speed greater than or equal to a cut in speed, or at least one of a voltage value in a stator terminal of the generator being greater than 0.1 pu due to residual magnetism or a DC link of the first inverter-based resource having a pre-charge of at least 0.1 pu.

9. The method of claim 8, wherein the one or more blackstarting preconditions comprises each of the grid breaker being open, the rotor circuit being shorted, the generator rotating at the speed greater than or equal to the cut in speed, and one of the voltage value in the stator terminal of the generator is greater than 0.1 pu due to residual magnetism or the pre-charge in the DC link of the first inverterbased resource is at least 0.1 pu.

10. The method of claim 9, further comprising opening a short of the rotor circuit after gradually increasing the terminal voltage of the generator and the bus voltage of the DC link of the first inverter-based resource to enable the grid forming control.

11. The method of any of the preceding claims, wherein the self-excitation process further comprises closing a synchronization switch of the first inverter-based resource after satisfying the one or more blackstarting preconditions to excite a stator of the generator.

12. The method of any of the preceding claims, wherein the blackstarting is completed without an additional external power generating source.

13. The method of any of the preceding claims, wherein the generator is a doubly fed induction generator.

14. A wind farm, comprising:a plurality of wind turbines comprising, at least, a first wind turbine, the first wind turbine comprising a generator electrically coupled to a power conversion assembly, the power conversion assembly comprising a line-side converter and a rotor-side converter coupled together via a DC link, the DC link comprising a DC link capacitor;a controller comprising at least one processor, the at least one processor configured to perform a plurality of operations, the plurality of operations comprising: satisfying one or more blackstarting preconditions;upon satisfaction of the one or more blackstarting preconditions, implementing a self-excitation process for the first wind turbine, the selfexcitation process comprising:utilizing at least one of the DC link capacitor or the first converter of the power conversion assembly; andself-exciting the generator by ramping up a DC bus setpoint of a DC link of the first inverter-based resource to gradually increase terminal voltage of the generator and a bus voltage of a DC link of the first wind turbine in a controlled manner; and blackstarting remaining wind turbines of the plurality of wind turbines using the self-excited first wind turbine.

15. The wind farm of claim 14, wherein the first wind turbine of the plurality of wind turbines is under grid forming control.

16. The wind farm of claim 15, wherein blackstarting the remaining wind turbines of the plurality of wind turbines using the terminal voltage further comprises: providing a constant voltage and frequency to the remaining wind turbines of the plurality of wind turbines via the first wind turbine.

17. The wind farm of claim 16, wherein providing the constant voltage and frequency to the remaining wind turbines of the plurality of wind turbines via the first wind turbine further comprises:starting a second converter of the power conversion assembly once the bus voltage of the DC link reaches rated voltage to establish a rated terminal voltage at a rated frequency using the grid forming control and disabling flux regulation by the first converter.

18. The wind farm of any of claims 14 to 17, wherein the one or more blackstarting preconditions comprises powering one or more auxiliary systems of the first wind turbine using an existing backup power system of the first wind turbine, wherein the one or more auxiliary systems comprises at least one of a control system, a pitch system, and a yaw system.

19. The wind farm of claims 14 to 18, wherein the one or more blackstarting preconditions comprises at least one of a grid breaker being open, a rotor circuit being shorted, the generator rotating at a speed greater than or equal to a cut in speed, or at least one of a voltage value in a stator terminal of the generator being greater than 0.1 pu due to residual magnetism or a DC link of the first wind turbine having a pre-charge of at least 0.1 pu.

20. The wind farm of any of claims 14 to 19, wherein the plurality of operations further comprises:closing a synchronization switch of the first wind turbine after satisfying the one or more blackstarting preconditions to excite a stator of the generator; andopening a short of the rotor circuit after gradually increasing the terminal voltage of the generator and the bus voltage of the DC link of the first wind turbine.

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