System and method for providing black-start of inverter-based resources for generation

Abstract

A method of synchronizing black start in a power plant connected to a power grid includes selecting, based on one or more parameters, at least a subset of a plurality of inverter-based resources having grid forming capabilities and an anchor power generation asset capable of facilitating black start at the power plant. A plurality of inverter-based resources are connected to the power grid via a transport network. The method includes utilizing a grid formation capability of the subset of the plurality of inverter-based resources for initial start-up to online the subset of the plurality of inverter-based resources and form a plurality of islands, thereby re-energizing the transport network portion and enabling recovery of one or more critical loads within a first period of time during the black start. During a subsequent second time period, the method includes further energizing the transmission network to fully restore the power grid to normal operation.

Description

Technical Field

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

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

[0003] Wind turbines can be classified into two types: fixed-speed turbines and variable-speed turbines. Traditionally, variable-speed wind turbines have been 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. The traditional 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 the penetration of wind power into the grid is low enough so as not to cause interference to the grid voltage amplitude and frequency. Thus, the wind turbine simply injects the specified current into the grid based on the fundamental voltage waveform. However, with the rapid growth of wind power, the penetration of wind power into some grids has increased to the extent that wind turbine generators have a significant impact on the grid voltage and frequency. When wind turbines are located in weak grids, wind turbine power fluctuations may cause an increase in the amplitude and frequency variations of 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] In addition, many existing renewable power generation converters, such as doubly-fed wind turbine generators, operate in a "grid-following" mode. Grid-following devices utilize fast current regulation loops to control the active and reactive power exchanged with the grid. More specifically, FIG. 1 illustrates the basic elements of the main circuit and converter control structure for a grid-following doubly-fed wind turbine generator. As shown, the active power reference to the converter is generated by an energy regulator (e.g., the turbine control section of the wind turbine). This is transmitted as a torque reference, which represents the lesser of the maximum available power from the energy source at that moment, or a curtailment command from a higher-level grid controller. The converter control then determines the current reference for the active component of the current to achieve the desired torque. Thus, the doubly-fed wind turbine generator includes a function to manage voltage and reactive power in a way that generates a command for the reactive component of the current. The wide-bandwidth current regulator then generates a command for the voltage to be applied by the converter to the system such that the actual current closely tracks the command.

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

[0006] In the early 1990s, the basic control structure for achieving the above grid-forming objectives was developed and field-verified for battery systems (e.g., see U.S. Patent No. 5,798,633, entitled "Battery Energy Storage Power Conditioning System"). The application to full-converter wind turbines and solar generators is 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 an implementation has been adopted for full-converter wind turbines.

[0007] The black-start capability of traditional generators is an important element in grid restoration after a power outage. As inverter-based resources replace many synchronous generators in the grid, there is an emerging grid need for inverter-based resources to provide a black-start capability similar to that of traditional generators. Grid-forming inverter-based resources may be able to provide black-start.

[0008] In view of the foregoing, the present disclosure relates to systems and methods for leveraging the grid-forming capabilities of multiple individual inverter-based resources to provide a coordinated black-start with a greater capacity than individual inverter-based resources acting independently. This improved capacity from large wind clusters will be comparable to the large capacity given by synchronous generators. SUMMARY

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

[0010] In an aspect, the present disclosure relates to a method for synchronous black-start in a power generation plant connected to a power grid. The method includes at least selecting a subset of a plurality of inverter-based resources having grid-forming capabilities and anchor generation assets that can contribute to black-start at the power generation plant based on one or more parameters. The plurality of inverter-based resources are connected to the power grid via a transmission network. The method includes utilizing the grid-forming capabilities of the subset of the plurality of inverter-based resources for an initial start-up to bring the subset of the plurality of inverter-based resources online and form a plurality of islands, thereby re-energizing a portion of the transmission network during a first time period of the black-start and achieving the restoration of one or more critical loads. During a subsequent second time period, the method includes further energizing the transmission network to fully restore the power grid to normal operation.

[0011] In another aspect, the present disclosure relates to a wind farm connected to an electric power grid. The wind farm includes a plurality of wind turbines connected to the electric power grid via a transmission network and a controller having at least one processor. The (one or more) processors are configured to perform a plurality of operations including, but not limited to, at least selecting a subset of the plurality of wind turbines having grid-forming capabilities and anchor generation assets capable of contributing to a black start based on one or more parameters, utilizing the grid-forming capabilities of the subset of the plurality of wind turbines for an initial startup, bringing the subset of the plurality of wind turbines online and forming a plurality of islands, thereby re-energizing a portion of the transmission network and achieving restoration of one or more critical loads during a first time period during a black start, and during a subsequent second time period, further energizing the transmission network to fully restore the electric power grid to normal operation.

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

[0013] A complete and enabling disclosure of the present invention, including the best mode thereof, for one of ordinary skill in the art, is set forth in the specification, which makes reference to the accompanying drawings, in which:

[0014] FIG. 1 illustrates a single-line diagram of a doubly-fed wind turbine generator according to a conventional configuration, the doubly-fed wind turbine generator having a structure for converter control for grid-following applications;

[0015] Figure 2 A perspective view illustrating an embodiment of a wind turbine according to the present disclosure;

[0016] Figure 3 A simplified internal view illustrating an embodiment of a nacelle according to the present disclosure;

[0017] Figure 4 A schematic diagram illustrating an embodiment of a wind turbine electrical power system suitable for use with the wind turbine shown in FIG. 1;

[0018] Figure 5 A schematic diagram illustrating an embodiment of a wind farm having a plurality of wind turbines according to the present disclosure;

[0019] Figure 6 A block diagram illustrating an embodiment of a controller according to the present disclosure;

[0020] Figure 7 A single-line diagram illustrating a doubly-fed wind turbine generator having converter control for grid-forming applications according to the present disclosure;

[0021] Figure 8 Flowchart of an embodiment of a method for synchronous black start in a power plant connected to a power grid according to the present disclosure;

[0022] Figure 9 Schematic network diagram of an embodiment of a system for providing synchronous black start in a power plant connected to a power grid according to the present disclosure;

[0023] Figure 10 Schematic diagram of an embodiment of a system for providing synchronous black start in a wind farm connected to a power grid according to the present disclosure, particularly illustrating the selection of the droop gain of the rotor side converter of the wind farm; and

[0024] Figure 11A and Figure 11B Schematic diagram of an embodiment of a system for providing synchronous black start in a wind farm connected to a power grid according to the present disclosure, particularly illustrating the grid forming control of the rotor side converter of a wind turbine using the selected droop gain. DETAILED DESCRIPTION

[0025] Embodiments of the present invention will now be referred to in detail, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the present invention, and not by way of limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the present invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield yet another embodiment. Accordingly, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0026] Increasing the level of renewable integration is associated with increasing the cost of grid security. Therefore, emerging grid codes require inverter-based resources to provide functionality traditionally provided by synchronous generators. An example of such functionality is for generating resources to provide black start capabilities. In view of the foregoing, the present disclosure relates to systems and methods for providing black start for inverter-based resources for grid forming. In an embodiment, for example, the method of the present disclosure can select a group of inverter-based resources having grid forming and grid following capabilities. Thus, such inverter-based resources can contribute to the black start of the grid based on, for example, wind conditions, wind farm layout, local load, power reserve requirements, etc. Then, the method of the present disclosure can establish a series of operations, such as bringing selected turbines and loads online to form an island. This step may further involve control design and coordination to ensure stable operation. The method of the present disclosure can also participate in grid restoration by exciting the grid.

[0027] Referring now to the drawings, Figure 2 FIG. shows a perspective view of one embodiment of a wind turbine 10 in accordance with 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 outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in alternative embodiments, the rotor 18 may include more or fewer than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotation of the rotor 18 such that kinetic energy can be converted from the wind into useful mechanical energy and subsequently into electrical energy. For example, the hub 20 may be rotatably coupled to a generator 24( Figure 3 ) located within the nacelle 16 to permit the generation of electrical energy.

[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 external to the wind turbine 10. Additionally, the controller 26 may be communicatively coupled to any number of components of the wind turbine 10 in order to control the operation of such components and / or effect corrective or control actions. Accordingly, 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 various operating modes (e.g., start-up or shutdown sequences), derate or rate up the wind turbine and / or individual components of the wind turbine 10.

[0029] Referring now to Figure 2, a simplified internal view of an embodiment of the nacelle 16 of the wind turbine 10 shown in FIG. 1 is illustrated. As shown, the generator 24 may be disposed within the nacelle 16 and supported on top of the base 46. Generally, the generator 24 may be coupled to the rotor 18 for generating electrical power from the rotational energy generated by the rotor 18. For example, as shown in the illustrated embodiment, the rotor 18 may include a rotor shaft 34 coupled to the hub 20 for rotation therewith. The rotor shaft 34 may in turn be rotatably coupled to the generator shaft 36 of the generator 24 through a gearbox 38. As is generally understood, in response to the rotation of the rotor blades 22 and the hub 20, the rotor shaft 34 may provide a low-speed, high-torque input to the gearbox 38. The gearbox 38 may then be configured to convert the low-speed, high-torque input into a high-speed, low-torque output to drive the generator shaft 36 and thus drive the generator 24.

[0030] The wind turbine 10 may also have one or more pitch drive mechanisms 32 communicatively coupled to the wind turbine controller 26, wherein each (one or more) pitch adjustment mechanism 32 is configured to rotate the pitch bearing 40 and thus rotate the individual (one or more) rotor blades 22 about their respective pitch axes 28. Additionally, as shown, the wind turbine 10 may include one or more yaw drive mechanisms 42 configured to change the angle of the nacelle 16 relative to the wind (e.g., by engaging a yaw bearing 44 of the wind turbine 10, which is disposed between the nacelle 16 and the tower 12 of the wind turbine 10).

[0031] Furthermore, 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 the wind turbine 10 may be measured, such as by using a suitable weather sensor 66. Suitable weather sensors may include, for example, light detection and ranging devices, acoustic detection and ranging devices, anemometers, wind vanes, barometers, radio detection and ranging devices, or any other sensing device that can provide wind direction information known in the art now or developed in the future. Some 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.

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

[0033] In Figure 4 the embodiments described above and as mentioned, the rotor 18 of the wind turbine 10 ( Figure 2 ) may optionally be coupled to a gearbox 38, which in turn is coupled to a generator 102, which may be a doubly-fed induction generator (DFIG). As shown, the DFIG 102 may be connected to a stator bus 104. Additionally, as shown, a power converter 106 may be connected to the DFIG 102 via a rotor bus 108 and to the stator bus 104 via a line-side bus 110. Thus, the stator bus 104 may provide output polyphase power (e.g., three-phase power) from the stator of the DFIG 102, and the rotor bus 108 may provide output polyphase power (e.g., three-phase power) from the rotor of the DFIG 102. The power converter 106 may also include a rotor-side converter (RSC) 112 and a line-side converter (LSC) 114. The DFIG 102 is coupled to the rotor-side converter 112 via the rotor bus 108. 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 modes in a three-phase pulse-width modulation (PWM) arrangement using one or more switching devices such as insulated-gate bipolar transistor (IGBT) switching elements. Additionally, the power converter 106 may be coupled to a converter controller 120 to control the operation of the rotor-side converter 112 and / or the line-side converter 114, as described herein. It should be noted that the converter controller 120 may be configured as an interface between the power converter 106 and the turbine controller 26 and may include any number of control devices.

[0035] In a typical configuration, various line contactors and circuit breakers (including, for example, a grid circuit breaker 122) may also be included to isolate various components necessary for the normal operation of the DFIG 102 during connection to and disconnection from a load (such as a power 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 power grid 124 via the grid circuit breaker 122. In alternative embodiments, fuses may replace some or all of the circuit breakers.

[0036] In operation, the AC power generated at the DFIG 102 by rotating the rotor 18 is supplied to the power grid 124 via a dual path defined by the stator bus 104 and the rotor bus 108. On the rotor bus side 108, sinusoidal polyphase (e.g., three-phase) alternating current (AC) power is supplied to the power converter 106. The rotor power side converter 112 converts the AC power supplied from the rotor bus 108 into direct current (DC) power and supplies the DC power to the DC link 116. As is generally understood, the switching elements (e.g., IGBTs) used in the bridge circuit of the rotor side power converter 112 can be modulated to convert the AC power supplied 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 power grid 124. In particular, the switching elements (e.g., IGBTs) used in the bridge circuit of the line side power converter 114 can be modulated to convert the DC power on the DC link 116 into AC power on the line side bus 110. The AC power from the power converter 106 can be combined with the power from the stator of the DFIG 102 to provide polyphase power (e.g., three-phase power) having a frequency that substantially remains at the frequency of the power grid 124 (e.g., 50 Hz or 60 Hz).

[0038] Furthermore, various circuit breakers and switches (such as the grid breaker 122, the system breaker 126, the stator synchronous switch 132, the converter breaker 134, and the line contactor 136) can be included in the wind turbine power system 100 to connect or disconnect the corresponding buses, for example, when the current flow is excessive and can damage the components of the wind turbine power system 100 or for other operational considerations. Additional protection components can also be included in the wind turbine power system 100.

[0039] Moreover, the power converter 106 can receive control signals from, for example, the local control system 176 via the converter controller 120. The control signals can in particular be based on the sensed state or operating characteristics of the wind turbine power system 100. Generally, the control signals provide control over the operation of the power converter 106. For example, feedback in the form of the sensed speed of the DFIG 102 can be used to control the conversion of the output power from the rotor bus 108 to maintain a correct and balanced polyphase (e.g., three-phase) power supply. Other feedback from other sensors can also be used by the controller(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, switch control signals (e.g., gate timing commands for IGBTs), stator synchronous control signals, and circuit breaker signals can be generated.

[0040] The power converter 106 also compensates for or adjusts the frequency of the three-phase power from the rotor for changes in wind speed, for example, at the hub 20 and the rotor blades 22. Thus, the mechanical and electrical rotor frequencies are decoupled and are substantially independent of the mechanical rotor speed to facilitate matching of the electrical stator and rotor frequencies.

[0041] In some conditions, the bidirectional nature of the power converter 106 and specifically the bidirectional nature of the LSC 114 and the RSC 112 facilitate feeding back at least some of the generated electrical power into the generator rotor. More specifically, electrical power can be transferred from the stator bus 104 to the line-side bus 110 and then through the line contactor 136 and into the power converter 106, specifically into the LSC 114, which acts as a rectifier and rectifies the sinusoidal three-phase AC power into DC power. The DC power is transferred into the DC link 116. The capacitor 118 facilitates reducing variations in the DC link voltage magnitude by facilitating reduction of the DC ripple sometimes associated with three-phase AC rectification.

[0042] The DC power is then transferred to the RSC 112, which converts the DC electrical power into three-phase sinusoidal AC electrical power by adjusting the voltage, current, and frequency. This conversion is monitored and controlled via the converter controller 120. The converted AC power is transferred from the RSC 112 to the generator rotor via the rotor bus 108. In this manner, reactive power control of the generator is facilitated by controlling the rotor current and voltage.

[0043] Now referring to Figure 5 , the wind turbine power system 100 described herein can be part of a wind farm 50. As shown, the wind farm 50 can include a plurality of wind turbines 52 (including the wind turbine 10 described above) and a total field-level controller 56. For example, as shown in the illustrated embodiment, the wind farm 50 includes twelve wind turbines, which include the wind turbine 10. However, in other embodiments, the wind farm 50 can include any other number of wind turbines, such as fewer than twelve wind turbines or more than twelve wind turbines. In one embodiment, the turbine controllers of the plurality of wind turbines 52 are communicatively coupled to the field-level controller 56, for example, by a wired connection (such as by connecting the turbine controller 26 via a suitable communication link 54 (e.g., a suitable cable)). Alternatively, the turbine controllers can be communicatively coupled to the field-level controller 56 by a wireless connection (such as by using any suitable wireless communication protocol known in the art). In additional embodiments, the field-level controller 156 is configured to send and receive control signals to and from the various wind turbines 52, such as, for example, to distribute real and / or reactive power demands across the wind turbines 52 of the wind farm 50.

[0044] Now referring to Figure 6, A block diagram of an embodiment of a suitable component that may be included in a controller (such as any one of the converter controller 120, turbine controller 26, and / or field-level controller 56 described herein) according to an example aspect of the present disclosure is shown. As shown, the controller may include one or more processors 58, a computer, or other suitable processing unit, and an associated memory device 60. The memory device 60 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, etc. disclosed herein).

[0045] As used herein, the term "processor" refers not only to an integrated circuit known in the art as being included in a computer, but also 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 include memory element(s), including but not limited to computer-readable media (such as random access memory (RAM)), computer-readable non-volatile media (such as flash memory), floppy disks, compact disc read-only memory (CD-ROM), magneto-optical discs (MOD), digital versatile discs (DVD), and / or other suitable memory elements.

[0046] Such memory device(s) 160 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 further include a communication interface 62 that is used to facilitate communication between the controller and various components of the wind turbine 10. The interface can include one or more circuits, terminals, pins, contacts, conductors, or other components for transmitting and receiving control signals. Furthermore, the controller may include a sensor interface 64 (such as one or more analog-to-digital converters) that is used to allow signals transmitted from sensors 66, 68 to be converted into signals that can be understood and processed by the processor(s) 58.

[0047] Now refer to Figure 7 , A schematic diagram of an embodiment of a grid-forming power system 200 according to the present disclosure, particularly showing a single-line diagram of a doubly-fed wind turbine generator 102 having an advanced control structure for grid-forming characteristics. In particular, as shown, the grid-forming power system 200 may include those described herein Figure 4Many of the same features among the same features, where components with the same reference numerals represent similar components. Additionally, as shown, the grid-forming system 200 may include a control structure for controlling the line-side converter, and the control structure for controlling the line-side converter 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 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 the 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] Additionally, 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 Figure 7 shown, the grid-forming power system 200 may include a stator voltage regulator 206 for providing such grid-forming characteristics. Additionally, as shown, the grid-forming power system 200 may include a grid voltage / VAR regulator 202, an inertia power regulator 204, a rotor current regulator 208, and a modulator 210.

[0049] More particularly, as will be explained, the grid-forming power system 200 includes an inner-loop current regulator structure and a fast stator voltage regulator, which are used to convert a voltage command from grid-forming control into a rotor current regulator command. Thus, the systems and methods of the present disclosure provide control of the rotor voltage of the generator 102 to meet higher-level commands for the magnitude and angle of the stator voltage. Such control must be relatively fast and insensitive to the current flowing in the stator of the doubly-fed wind turbine generator 102.

[0050] Now referring to Figure 8 and Figure 9 , the present disclosure relates to a method 250 and a system 300 for synchronous black start in a power generation field connected to a power grid according to the present disclosure. In particular, Figure 8 FIG. illustrates a flowchart of an embodiment of a method 250 for synchronous black start in a power generation field connected to a power grid according to the present disclosure, while Figure 9 FIG. illustrates a schematic diagram of a system 300 for synchronous black start in a wind farm 301 connected to a power grid according to the present disclosure. Generally, reference is made herein to Figures 2 - 7The method 250 will be described with respect to a wind turbine 10 and a wind farm 50. However, it should be appreciated that, in addition to wind turbines having any other suitable configuration, any inverter-based resource may be utilized to implement the disclosed method 250. Additionally, although Figure 8 Steps are depicted for purposes of illustration and discussion as being performed in a particular order, but the methods discussed herein are not limited to any particular order or arrangement. Using the disclosures provided herein, those skilled in the art will appreciate that the various steps of the methods disclosed herein may be omitted, rearranged, combined, and / or adjusted in various ways without departing from the scope of the present disclosure.

[0051] As shown at (252), the method 250 may include receiving a black start signal from a controller, such as a system-level controller. Upon receiving the black start signal, as shown at (254), the method 250 includes monitoring a wind forecast for a particular period of time, such as from about four (4) hours to about six (6) hours (and up to 24 hours as needed based on grid code requirements).

[0052] As shown at (256), the method 250 includes selecting at least a subset of a plurality of wind turbines 302 having grid-forming capabilities, grid-following capabilities, and anchor generation assets capable of contributing to a black start at a wind farm 301 based on one or more parameters. For example, in an embodiment, the subset of the plurality of wind turbines 302 at the wind farm 301 may include a main wind turbine 303 (e.g., WTG1) and any number of additional wind turbines 302 (e.g., WTG2 and WTG3). Additionally, as shown, the subset of the plurality of wind turbines 302 may be part of a first wind farm (e.g., wind farm 1) located at a first geographical location, while the remaining wind turbines 302 may be located at a second geographical location (e.g., wind farm 2). Additionally, as Figure 9 shown, the anchor generation asset 304 may be an anchor generator (such as an energy storage device (ES) or a diesel generator (DG)) at a wind farm(s). Additionally, in an embodiment, the plurality of wind turbines 302 are connected to an electrical grid via a transmission network. Thus, as shown, the wind turbines 302 in wind farm 1 and wind farm 2 and the anchor generation asset(s) 304 are configured to synchronize with the main wind turbine 303.

[0053] Additionally, in an embodiment, the parameter(s) for determining whether an individual is capable of contributing to a black start may include one or more environmental conditions, the layout of the wind turbines 302, one or more local loads (e.g., Figure 9Load_SS, Load 1, Load 2, Load 3, the load, etc., one or more power reserve requirements, and / or combinations thereof. Thus, in an embodiment, a selected subset of the plurality of wind turbines 302 may include wind turbines 302 having the largest capacity, wind range, electrical distance, presence of an energy storage device, state of charge, availability of an anchor power generation asset, etc. In addition, as shown, in an embodiment, method 250 may further include excluding wind turbines 302 indicating that the predicted wind is less than the cut - in wind speed or greater than the cut - out wind speed.

[0054] Still referring Figure 8 , as shown at (258), method 250 may include identifying one or more local loads for a subset of the plurality of wind turbines 302. For example, in an embodiment, the (one or more) local loads may include the block load connection capacity, controllable loads, and uncontrollable loads of a wind farm. In addition, as shown at (260), method 250 includes setting a reserve margin and / or a timer for black start based on one or more grid code requirements.

[0055] Thus, as shown at (262), method 250 includes determining whether a subset of the plurality of wind turbines 302 is the first group of wind turbines to come online. If so, then method 250 includes utilizing the grid - forming ability of the subset of the plurality of wind turbines 302 for initial startup to bring the subset of the plurality of wind turbines 302 online and form a plurality of islands (e.g., 306, 308), thereby re - energizing the transmission network portion during a first time period during the black start and achieving the restoration of one or more critical loads; and

[0056] More specifically, as Figure 8 shown at (264), utilizing the grid - forming ability of a subset of the plurality of wind turbines 302 for initial startup may include at least using an anchor power generation asset and the grid - following ability of the subset of the plurality of wind turbines 302 or at least one of one or more local loads to soft - start the subset of the plurality of wind turbines 302. For example, in an embodiment, soft - starting the subset of the plurality of wind turbines 302 may include setting the voltage reference (e.g., Figure 9 V ref1 ) of the subset of the plurality of wind turbines 302 to the nominal voltage, setting the reference frequency (e.g., Figure 9 f Figure 9 ) of the subset of the plurality of wind turbines 302 to the nominal frequency (e.g., nom f Figure 9 ) of, and utilizing the grid - following ability (GFL) for the subset of the plurality of wind turbines 302 to determine the active power reference (e.g., P) and the reactive power reference (e.g., Q) (e.g., for GFL control of P, Q in

[0057] Return reference Figure 8 , as shown at (264), using the grid-forming capabilities of a subset of the plurality of wind turbines 302 for initial startup can further include using virtual impedances (e.g., Figure 10 Rd1 and Rd2 in Figure 10 to Figure 11A and Figure 11B ) to coordinate a subset of the plurality of wind turbines 302 to maintain the corresponding voltages and frequencies of the subset of the plurality of wind turbines 302, e.g., to make a tradeoff between inrush current reduction and voltage maintenance. For example, in an embodiment, using a dynamic virtual impedance to coordinate a subset of the plurality of wind turbines 302 to maintain the corresponding voltages and frequencies of the subset of the plurality of wind turbines 302 can include using a dynamic virtual impedance to control a power converter (such as the rotor-side converter of each wind turbine 302 (see, e.g.,

[0058] Still referring to Figure 8 , in an embodiment, as shown at (264), using the grid-forming capabilities of a subset of the plurality of wind turbines 302 for initial startup can include synchronizing or spacing the timings of startup of the wind turbines 302 in the subset to improve coordination.

[0059] Furthermore, in an embodiment, as shown at (266), using the grid-forming capabilities of a subset of the plurality of wind turbines 302 for initial startup can include monitoring the voltages and frequencies of the subset of the plurality of wind turbines 302 to maintain their stability. More specifically, as shown, method 250 can include ensuring that various relationships are satisfied to ensure the stability of black start. The following exemplary relationships are provided as relationships (1) to (3): P gen –P load –P loss = 0 Relationship (1) 0 < P gen < P max -P reserve Relationship (2) Q gen –Q abs = 0 Relationship (3)

[0060] Specifically, in an embodiment, method 250 may include providing an actual power balance between the total generated power (e.g., Pgen) and the total consumed power including losses (e.g., Pload + Ploss). Additionally, in an embodiment, method 250 may include providing maximum and minimum limits (e.g., Pmax, Preserve) on the actual power generation (e.g., Pgen) from the power generating wind turbines. Further, in an embodiment, method 250 may include providing a reactive power balance between the generated reactive power (e.g., Qgen) and the absorbed reactive power (e.g., Qabs).

[0061] As shown at (268), method 250 further includes determining whether stability can be maintained by a subset of the plurality of wind turbines. For example, in an embodiment, determining whether the stability can be maintained by the subset of the plurality of wind turbines may include comparing the measured voltage and the current voltage, and determining based on the comparison whether the stability can be maintained by the subset of the plurality of inverter-based resources.

[0062] If the stability cannot be maintained by a subset of the plurality of wind turbines, method 250 includes selecting a different subset of the plurality of wind turbines having grid-forming capabilities at the wind farm for soft start. For example, in an embodiment, method 250 may allow a certain number of attempts (such as up to three (3) times) to maintain stability before moving to another different subset of wind turbines.

[0063] If the stability can be maintained by a subset of the plurality of wind turbines, method 250 continues at (270). Specifically, during a subsequent second time period, the method 250 includes further exciting the transmission network to fully restore the power grid to normal operation. More specifically, in an embodiment, as shown at (270), method 250 for further exciting the transmission network to fully restore the power grid to normal operation may include using the grid-following capabilities of the remaining portion of the plurality of wind turbines or at least one of one or more local loads to soft start the remaining portion of the plurality of wind turbines. In such an embodiment, for example, soft starting the remaining portion of the plurality of wind turbines 302 may include initially setting the voltage reference (e.g., Figure 9 of V ref2 ) to the measured voltage (e.g., Figure 9 of V _measured ), and subsequently setting the voltage reference (e.g., Figure 9 of V ref2 ) to the nominal voltage (e.g., V nom ), and setting the reference frequency (e.g., f ref)Set to the nominal frequency (e.g., f nom ). In addition, as shown, in an embodiment, soft starting the remainder of the plurality of wind turbines 302 may further include determining the active power reference and the reactive power reference (e.g., P and Q) using the grid-following capabilities of the remainder of the plurality of wind turbines 302.

[0064] Thus, as Figure 8 shown at (272) of, method 250 includes updating the reserve margin and the load connection. In addition, method 250 may include monitoring the voltage and frequency of the remainder of the plurality of wind turbines to maintain their stability. More specifically, as shown and mentioned, method 250 may include ensuring that various relationships (e.g., relationships (1) to (3) provided herein) are satisfied to ensure the stability of the black start using the remainder of the plurality of wind turbines.

[0065] Thus, the grid-forming wind turbines in system 300 can contribute to the coordination of black starts similar to those of synchronous generators and the start-up of wind turbines. More specifically, as mentioned, the plurality of wind turbines 302 may be located in different regions (e.g., as represented by wind farm 1 and wind farm 2), such that each wind turbine in different regions may contribute differently to the black start. For example, in an embodiment, up to 100 or more wind turbines may contribute to the black start, where the coordination between the wind turbines improves the excitation ability. In addition, in an embodiment, larger and fewer wind turbines may be selected relative to smaller and more wind turbines. In addition, in an embodiment, wind turbines with a greater electrical distance may be selected instead of those with a closer electrical distance to improve stability. Thus, in such an embodiment, system 300 is configured to generate virtual impedances (e.g., Z10, Z12, and Z23) based on, for example, the electrical distance. In addition, in an embodiment, system 300 may apply time synchronization for the control of grid excitation.

[0066] Thus, system 300 is configured to set a frequency reference for a selected subset of wind turbines 302. In such an embodiment, the frequency reference may be determined based on one or more local loads (e.g., Load_SS, Load 1, Load 2, Load 3, etc.), GPS, or TSO. Thus, in an embodiment, other grid-forming wind turbine groups (such as Figure 9 those in wind farm 2 in) are connected to the grid formed by the first group (such as Figure 9 those in wind farm 1 in) at the reference frequency.

[0067] Other grid-following groups of wind turbines can be connected to the grid after the first group / subset. Additionally, in embodiments, the inrush current can be limited by forming a wind turbine with a soft start grid, i.e., starting with a high virtual impedance and gradually decreasing it. Additionally, in embodiments, the system 300 is configured to achieve reactive power sharing.

[0068] Accordingly, the method 250 and system 300 of the present disclosure are aware of information related to adjacent wind turbines 302, enabling coordination between the startups of each wind turbine. Thus, the method 250 and system 300 of the present disclosure provide an improved response time to power outages and an improved ability to provide black start on individual wind turbines operating independently. Additionally, the method 250 and system 300 of the present disclosure are configured to monitor the voltage phase and magnitude of each wind turbine. Accordingly, in embodiments, the method 250 and system 300 of the present disclosure can include reference control parameter communication data that includes a timestamp and an actual parameter value. Thus, the wind turbine receiving the data is able to adjust its control. Accordingly, in embodiments, the method 250 and system 300 of the present disclosure can operate when connected to a loaded and unloaded grid by correspondingly scheduling loads (e.g., using controllable loads) during the startup sequence. Additionally, in embodiments, the method 250 and system 300 of the present disclosure operate by controlling the phase of the voltage while exciting different wind turbines during black start to provide system-level recovery.

[0069] Now referring to Figure 10 , a schematic diagram illustrating an embodiment of droop gain selection for a rotor-side converter of a wind farm according to the present disclosure. As used herein, the droop gain 310 (e.g., Figure 10 , Figure 11A and Figure 11B 's Rd1, Rd2) corresponds to a virtual impedance that can be incorporated into the rotor-side converter (RSC) 305 (e.g., RSC control) of the wind turbine 302 for better synchronization. Specifically, as shown, the droop gain 310 (e.g., Figure 10 , Figure 11A and Figure 11B 's Rd1, Rd2) can be a function of the distance between wind turbines 302, the equivalent line impedance, etc. The actual impedance 311 of each wind turbine 302 in the wind turbines 302 (e.g., due to physical cable / line impedance) is in Figure 10Shown in the figure are Rx1 and Rx2. Wind turbines that are electrically close to each other may have a coupling effect and may ultimately lead to instability in the system. Therefore, by using control to select a higher internal virtual impedance, the wind turbines 302 can be made to be effectively farther apart (i.e., electrically), and the inrush current in the transformers and cables can be limited, thereby ensuring stable operation. In addition, the higher virtual impedance ensures smooth synchronization between the wind turbines 302 by reducing the coupling between the wind turbines 302.

[0070] Now refer to Figure 11A and Figure 11B , which is a schematic diagram showing an embodiment of grid-forming control of a first rotor-side converter (e.g., RSC1) and a second rotor-side converter (e.g., RSC2) of a first wind turbine and a second wind turbine using selected droop gains according to the present disclosure. Specifically, the internal virtual impedances (e.g., Rd1, Rd2) can be selected using the following relationships (4) and (5): R d1 = k1 + k / (cable impedance of WT1) Relationship (4) R d2 = k1 + k / (cable impedance of WT2) Relationship (5) where k1 is the nominal virtual impedance and depends on the grid short-circuit ratio (SCR), and k is a factor that can be set higher during startup and stabilized to a lower value during steady state.

[0071] Therefore, as shown, the virtual impedances (e.g., Rd1, Rd2) can be implemented into the RSC control by multiplying the virtual impedance by the stator current feedback, as shown at 312. In addition, as shown at 314, a limit can be imposed, and the output 315 from the limiter 314 can be integrated into the control path 316 of the rotor-side converter(s). Specifically, as shown, the output 315 can be subtracted from the control signal 317 in the control path 316 to determine the voltage signal 319 (e.g., Vm_cmd_xy). Therefore, as shown, the stator voltage regulator 318 and the rotor current regulator 320 can use the voltage signal 319 to generate gate pulses for the corresponding rotor-side converters.

[0072] Further aspects of the present invention are provided by the subject matter of the following clauses:

[0071] Thus, as shown, a virtual impedance (e.g., Rd1, Rd2) can be implemented into the RSC control by multiplying the virtual impedance by the stator current feedback, as shown at 312. Additionally, as shown at 314, a limitation can be imposed, and the output 315 from the limiter 314 can be integrated into the control path 316 of the (one or more) rotor side converters. Specifically, as shown, the output 315 can be subtracted from the control signal 317 in the control path 316 to determine a voltage signal 319 (e.g., Vm_cmd_xy). Thus, as shown, the stator voltage regulator 318 and the rotor current regulator 320 can use the voltage signal 319 to generate gate pulses for the respective rotor side converters.

[0072] Further aspects of the present invention are provided by the subject matter of the following clauses:

[0073] A method for synchronously black starting in a power generation plant connected to a power grid, the method comprising: at least selecting a subset of a plurality of inverter-based resources having grid-forming capabilities and anchor generation assets capable of contributing to a black start at the power generation plant based on one or more parameters, the plurality of inverter-based resources being connected to the power grid via a transmission network; utilizing the grid-forming capabilities of the subset of the plurality of inverter-based resources for an initial start-up to bring the subset of the plurality of inverter-based resources online and form a plurality of islands, thereby re-energizing a portion of the transmission network during a first time period of the black start and achieving restoration of one or more critical loads; and during a subsequent second time period, further energizing the transmission network to fully restore the power grid to normal operation.

[0074] The method according to any of the preceding clauses, further comprising identifying one or more local loads for the subset of the plurality of inverter-based resources, the one or more local loads including at least one of a block load connection capability, a controllable load, and an uncontrollable load of the power generation plant.

[0075] The method according to any of the preceding clauses, wherein the one or more parameters include at least one of the following: one or more environmental conditions, a layout of the inverter-based resources, the one or more local loads, one or more power reserve requirements, or a combination thereof.

[0076] The method according to any of the preceding clauses, wherein utilizing the grid-forming capabilities of the subset of the plurality of inverter-based resources for an initial start-up further comprises: soft starting the subset of the plurality of inverter-based resources using at least the anchor generation assets and a grid-following capability of the subset of the plurality of inverter-based resources or at least one of the one or more local loads.

[0077] The method according to any of the preceding clauses, wherein soft starting the subset of the plurality of inverter-based resources using at least the grid-following capabilities of the anchor generation assets and the subset of the plurality of inverter-based resources or at least one of one or more local loads further comprises: setting a voltage reference of the subset of the plurality of inverter-based resources to a nominal voltage; setting a reference frequency of the subset of the plurality of inverter-based resources to a nominal frequency; and determining an active power reference and a reactive power reference using the grid-following capabilities for the subset of the plurality of inverter-based resources.

[0078] The method according to any of the preceding clauses, wherein using the grid-forming capabilities of the subset of the plurality of inverter-based resources for initial startup further comprises: using a dynamic virtual impedance to coordinate the subset of the plurality of inverter-based resources to maintain corresponding voltages and frequencies of the subset of the plurality of inverter-based resources.

[0079] The method according to any of the preceding clauses, wherein using the grid-forming capabilities of the subset of the plurality of inverter-based resources for initial startup further comprises: monitoring voltages and frequencies of the subset of the plurality of inverter-based resources to maintain their stability.

[0080] The method according to any of the preceding clauses, wherein the plurality of inverter-based resources are a plurality of wind turbines, and wherein using a dynamic virtual impedance to coordinate the subset of the plurality of inverter-based resources to maintain corresponding voltages and frequencies of the subset of the plurality of inverter-based resources further comprises: using the dynamic virtual impedance in a power converter controlling each wind turbine in the subset of the plurality of wind turbines to provide a stable startup of the subset of the plurality of wind turbines.

[0081] The method according to any of the preceding clauses further comprises determining the dynamic virtual impedance based on a combination of at least two of the following: one or more gains, one or more factors related to the states of the plurality of inverter-based resources, cable impedance, distance between adjacent inverter-based resources, transformer impedance in an excitation path, and nominal impedance, the states of the plurality of inverter-based resources including at least one of startup or steady state.

[0082] The method according to any of the preceding clauses, wherein using the grid-forming capabilities of the subset of the plurality of inverter-based resources for initial startup further comprises: synchronizing or spacing apart the timings of startups of the subset of the plurality of inverter-based resources to improve coordination.

[0083] The method according to any of the foregoing clauses further includes: determining whether the stability can be maintained by the subset of the plurality of inverter-based resources; if the stability cannot be maintained by the subset of the plurality of inverter-based resources, selecting a different subset of the plurality of inverter-based resources having grid-forming capabilities at the power plant for the soft start; and if the stability can be maintained by the subset of the plurality of inverter-based resources, using the grid-following capabilities of the remaining subset of the plurality of inverter-based resources or at least one of the one or more local loads to soft start the remainder of the plurality of inverter-based resources.

[0084] The method according to any of the foregoing clauses, wherein determining whether the stability can be maintained by the subset of the plurality of inverter-based resources further includes: comparing the measured voltage and the current voltage, and determining whether the stability can be maintained by the subset of the plurality of inverter-based resources based on the comparison.

[0085] The method according to any of the foregoing clauses, wherein using the grid-following capabilities of the subset of the plurality of inverter-based resources or at least one of the one or more local loads to soft start the remainder of the plurality of inverter-based resources further includes: initially setting the voltage reference of the remainder of the plurality of inverter-based resources to the measured voltage and subsequently setting the voltage reference to the nominal voltage; setting the reference frequency of the remaining resources of the plurality of inverter-based resources to the nominal frequency; and using the grid-following capabilities of the remaining resources of the plurality of inverter-based resources to determine the active power reference and the reactive power reference.

[0086] The method according to any of the foregoing clauses, wherein the anchor generation asset is an anchor generator at the power plant.

[0087] A wind farm connected to a power grid, the wind farm including: a plurality of wind turbines connected to the power grid via a transmission network; a controller including at least one processor configured to perform a plurality of operations, the plurality of operations including: at least selecting a subset of the plurality of wind turbines having grid-forming capabilities and an anchor generation asset capable of contributing to a black start based on one or more parameters; using the grid-forming capabilities of the subset of the plurality of wind turbines for an initial start-up to bring the subset of the plurality of wind turbines online and form a plurality of islands, thereby re-energizing a portion of the transmission network during a first time period during the black start and achieving the restoration of one or more critical loads; and during a subsequent second time period, further energizing the transmission network to fully restore the power grid to normal operation.

[0088] A wind farm according to any of the preceding clauses, wherein the one or more parameters include at least one of the following: one or more environmental conditions, the layout of the inverter-based resources, one or more local loads, one or more power reserve requirements, or combinations thereof.

[0089] A wind farm according to any of the preceding clauses, wherein using the grid-forming ability of the subset of the plurality of wind turbines for initial startup further includes: soft-starting the subset of the plurality of wind turbines using at least one of the anchor generation assets and the grid-following ability of the subset of the plurality of inverter-based resources or a local load.

[0090] A wind farm according to any of the preceding clauses, wherein soft-starting the subset of the plurality of wind turbines using at least one of the anchor generation assets and the grid-following ability of the subset of the plurality of wind turbines or a local load further includes: for the subset of the plurality of inverter-based resources, setting the voltage reference to the nominal voltage and setting the reference frequency to the nominal frequency; for the subset of the plurality of inverter-based resources, setting the reference frequency to the nominal frequency; and using the grid-following ability of the subset of the plurality of wind turbines to determine the active power reference and the reactive power reference.

[0091] A wind farm according to any of the preceding clauses, wherein using the grid-forming ability of the subset of the plurality of wind turbines for initial startup further includes: using a dynamic virtual impedance to coordinate the subset of the plurality of wind turbines to maintain the corresponding voltage and frequency of the subset of the plurality of wind turbines, wherein using a dynamic virtual impedance to coordinate the subset of the plurality of wind turbines to maintain the corresponding voltage and frequency of the subset of the plurality of wind turbines further includes using a dynamic virtual impedance in the power converter controlling each wind turbine in the subset of the plurality of wind turbines to provide a stable startup of the subset of the plurality of wind turbines.

[0092] A wind farm according to any of the preceding clauses, wherein using the grid-forming ability of the subset of the plurality of wind turbines for initial startup further includes: synchronizing or spacing apart the timing of the startup of the subset of the plurality of wind turbines to improve coordination.

[0093] This written description uses examples, including the best mode, to disclose the invention and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any associated method. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. If such other examples have structural elements that are identical to the literal language of the claims or if they contain equivalent structural elements with insubstantial differences from the literal language of the claims, they are expected to fall within the scope of the claims.

Claims

1. A method for synchronously black-starting in a power generation plant connected to a power grid, the method comprising: selecting at least a subset of a plurality of inverter-based resources having grid-forming capabilities at the power generation plant, and anchor generation assets capable of contributing to a black start, based on one or more parameters, the plurality of inverter-based resources being connected to the power grid via a transmission network; utilizing the grid-forming capabilities of the subset of the plurality of inverter-based resources for an initial start-up to bring the subset of the plurality of inverter-based resources online and form a plurality of islands, thereby re-energizing a portion of the transmission network during a first time period of the black start and achieving the restoration of one or more critical loads; and during a subsequent second time period, further energizing the transmission network to fully restore the power grid to normal operation.

2. The method according to claim 1, further comprising identifying one or more local loads for the subset of the plurality of inverter-based resources, the one or more local loads including at least one of a block load connection capacity of the power generation plant, a controllable load, and an uncontrollable load.

3. The method according to claim 2, wherein The one or more parameters include at least one of one or more environmental conditions, a layout of the inverter-based resources, the one or more local loads, one or more power reserve requirements, or a combination thereof.

4. The method according to claim 2, wherein Utilizing the grid-forming capabilities of the subset of the plurality of inverter-based resources for an initial start-up further comprises: soft-starting the subset of the plurality of inverter-based resources using at least the anchor generation assets and at least one of a grid-following capability of the subset of the plurality of inverter-based resources or the one or more local loads.

5. The method according to claim 4, wherein, Soft-starting the subset of the plurality of inverter-based resources using at least the anchor generation assets and at least one of a grid-following capability of the subset of the plurality of inverter-based resources or the one or more local loads further comprises: setting a voltage reference of the subset of the plurality of inverter-based resources to a nominal voltage; setting a reference frequency of the subset of the plurality of inverter-based resources to a nominal frequency; and utilizing the grid-following capability for the subset of the plurality of inverter-based resources to determine an active power reference and a reactive power reference.

6. The method according to claim 5, wherein Utilizing the grid-forming capabilities of the subset of the plurality of inverter-based resources for an initial start-up further comprises: using a dynamic virtual impedance to coordinate the subset of the plurality of inverter-based resources to maintain corresponding voltages and frequencies of the subset of the plurality of inverter-based resources.

7. The method according to claim 6, wherein, Utilizing the grid-forming capabilities of the subset of the plurality of inverter-based resources for an initial start-up further comprises: monitoring the voltages and frequencies of the subset of the plurality of inverter-based resources to maintain their stability.

8. The method according to claim 6, wherein The plurality of inverter-based resources are a plurality of wind turbines, wherein using a dynamic virtual impedance to coordinate a subset of the plurality of inverter-based resources to maintain corresponding voltages and frequencies of the subset of the plurality of inverter-based resources further comprises: Use the dynamic virtual impedance in the control of the power converters of each of the wind turbines in the subset of the plurality of wind turbines to provide a stable start-up of the subset of the plurality of wind turbines.

9. The method according to claim 6, further comprising determining the dynamic virtual impedance based on a combination of at least two of the following: one or more gains, one or more factors related to the state of the plurality of inverter-based resources, cable impedance, distance between adjacent inverter-based resources, transformer impedance in the excitation path, and nominal impedance, the state of the plurality of inverter-based resources including at least one of start-up or steady state.

10. The method according to claim 9, wherein, Utilizing the grid-forming capability of the subset of the plurality of inverter-based resources for initial start-up further comprises: Synchronizing or spacing the timing of the start-up of the subset of the plurality of inverter-based resources to improve coordination.

11. The method according to claim 7, further comprising: Determining whether the stability can be maintained by the subset of the plurality of inverter-based resources; If the stability cannot be maintained by the subset of the plurality of inverter-based resources, selecting a different subset of the plurality of inverter-based resources having grid-forming capability at the power plant for the soft start; And If the stability can be maintained by the subset of the plurality of inverter-based resources, using the grid-following capability of the remaining subset of the plurality of inverter-based resources or at least one of the one or more local loads to soft start the remaining subset of the plurality of inverter-based resources.

12. The method according to claim 11, wherein, Determining whether the stability can be maintained by the subset of the plurality of inverter-based resources further comprises comparing the measured voltage and the current voltage and determining based on the comparison whether the stability can be maintained by the subset of the plurality of inverter-based resources.

13. The method according to claim 11, wherein Using the grid-following capability of the subset of the plurality of inverter-based resources or at least one of the one or more local loads to soft start the remaining portion of the plurality of inverter-based resources further comprises: Initially setting the voltage reference of the remaining portion of the plurality of inverter-based resources to the measured voltage and subsequently setting the voltage reference to the nominal voltage; Setting the reference frequency of the remaining portion of the plurality of inverter-based resources to the nominal frequency; and Utilizing the grid-following capability for the remaining portion of the plurality of inverter-based resources to determine the active power reference and the reactive power reference.

14. The method according to claim 1, wherein, The anchor generation asset is an anchor generator at the power plant.

15. A wind farm connected to a power grid, the wind farm comprising: A plurality of wind turbines connected to the power grid via a transmission network; A controller including at least one processor configured to perform a plurality of operations, the plurality of operations including: At least select a subset of the plurality of wind turbines having grid-forming capability and an anchor generation asset capable of contributing to a black start based on one or more parameters; Utilize the grid-forming capabilities of the subset of the plurality of wind turbines for initial startup to bring the subset of the plurality of wind turbines online and form a plurality of islands, thereby re-energizing the transmission network section during a first time period of the black start and achieving the restoration of one or more critical loads; and During a subsequent second time period, further energize the transmission network to fully restore the power grid to normal operation.

16. The wind farm according to claim 15, wherein, The one or more parameters include at least one of one or more environmental conditions, the layout of the inverter-based resources, one or more local loads, one or more power reserve requirements, or a combination thereof.

17. The wind farm according to claim 15, wherein Utilizing the grid-forming capabilities of the subset of the plurality of wind turbines for initial startup further includes: Soft-starting the subset of the plurality of inverter-based resources by using at least one of the anchor generation assets and the grid-following capabilities of the subset of the plurality of wind turbines or local loads.

18. The wind farm according to claim 17, wherein, Soft-starting the subset of the plurality of wind turbines by using at least one of the anchor generation assets and the grid-following capabilities of the subset of the plurality of wind turbines or the local loads further includes: For the subset of the plurality of inverter-based resources, setting the voltage reference to the nominal voltage and setting the reference frequency to the nominal frequency; For the subset of the plurality of inverter-based resources, setting the reference frequency to the nominal frequency; and Utilizing the grid-following capabilities of the subset of the plurality of wind turbines to determine the active power reference and the reactive power reference.

19. The wind farm according to claim 18, wherein, Utilizing the grid-forming capabilities of the subset of the plurality of wind turbines for initial startup further includes: Using dynamic virtual impedance to coordinate the subset of the plurality of wind turbines to maintain the corresponding voltages and frequencies of the subset of the plurality of wind turbines, wherein using dynamic virtual impedance to coordinate the subset of the plurality of wind turbines to maintain the corresponding voltages and frequencies of the subset of the plurality of wind turbines further includes using the dynamic virtual impedance in the power converters that control each wind turbine in the subset of the plurality of wind turbines to provide a stable startup for the subset of the plurality of wind turbines.

20. The wind farm according to claim 19, wherein, Utilizing the grid-forming capabilities of the subset of the plurality of wind turbines for initial startup further includes: Synchronizing or spacing apart the timings of the startups of the subset of the plurality of wind turbines to improve coordination.

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