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 (IBRs) and a power generating device includes starting the power generating device at a pre-defined voltage with the power generating farm disconnected from an electrical grid. Each IBR is connected to a point of common connection (PCC) via a respective transformer and a first switch. The method includes energizing the respective transformers connected to the PCC at the pre-defined voltage. Further, the method includes initiating the blackstarting of the power generating farm by implementing a blackstart process of at least one IBR of the plurality of IBRs. Moreover, the method includes disconnecting the power generating device from the PCC and connecting a transmission line having the PCC to the electrical grid to facilitate energization of the transmission line through the IBR. The method also includes ramping up an output voltage of the IBR to a nominal voltage value.

Description

SYSTEM AND METHOD FOR PROVIDING BLACKSTART OF GRID-FORMING INVERTER-BASED RESOURCESFIELD

[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 ty pically 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 ty pes: 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 grow th 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 arelocated 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 cunent control and adversely affect the performance of loads connected to the network.

[0004] Furthermore, many existing renewable generation converters, such as double-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 double-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 double-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 loadcharacteristic, 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 and a power generating device. Each of the plurality of inverter-based resources is connected to a point of common connection (PCC) via a respective transformer and a first switch.With the power generating farm disconnected from an electrical grid, the method includes starting the power generating device at a pre-defined voltage. The method also includes energizing the respective transformers connected to the PCC at the predefined voltage. Further, the method includes initiating the blackstarting of the power generating farm by implementing a blackstart process of at least one inverter-based resource of the plurality of inverter-based resources. Moreover, the method includes disconnecting the power generating device from the PCC. In addition, the method includes connecting a transmission line having the PCC to the electrical grid to facilitate energization of the transmission line through the at least one inverter-based resource of the plurality' of inverter-based resources. Further, the method includes ramping up an output voltage of the at least one inverter-based resource to a nominal voltage value.

[0011] In another aspect, the present disclosure is directed to a wind farm having a main transformer, a plurality of local transformers, a plurality of local switches, and a plurality’ of wind turbines. Each of the plurality of wind turbines is connected to a point of common connection (PCC) via a respective transformer of the plurality of local transformers and a first switch of the plurality of local switches. The wind farm also includes a power generating device and a controller having at least one processor. The processor(s) is configured to perform a plurality' of operations, including but not limited to, with the wind farm disconnected from an electrical grid, starting the power generating device at a pre-defined voltage, energizing the respective transformers connected to the PCC at the pre-defined voltage, implementing a blackstart process of at least one wind turbine of the plurality of wind turbines, the at least one wind turbine being under grid forming control, disconnecting the power generating device from the PCC, connecting a transmission line having the PCC to the electrical grid to facilitate energization of the transmission line through the at least one wind turbine of the plurality7of wind turbines, and ramping up an output voltage of the at least one wind turbine to a nominal voltage value.

[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 double-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 double-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 a power generating farm, such as wind farm, having blackstart capability’ according to the present disclosure;

[0022] FIG. 9 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; and

[0023] FIG. 10 illustrates a schematic diagram of another embodiment of a power generating farm, such as wind farm, having blackstart capability 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] Generally, the present disclosure is directed to systems and methods for blackstarting a power generating farm. In particular, in an embodiment, the present disclosure is directed to techniques to energize pad mount transformers and high- voltage (HV) / medium-voltage (MV) feeder lines in a wind farm, while blackstarting under grid forming control. Accordingly, systems and methods of the present disclosure are configured to minimize inrush currents during energization of the wind farm following either passive energization via feeder line capacitors or increasing the voltage of the wind turbines in the wind farm in an exponential manner, which has come online after grid loss following blackstart.

[0026] More specifically, systems and methods of the present disclosure is configured to initiate blackstart steps considering different architectures of wind turbine strings. Further, the systems and methods of the present disclosure consider both scenarios where an automatic switchgear can be present or not at the pad mount transformers. The steps follow charging of the DC link voltage of an individual wind turbine via an anchor generator, operating at a lower voltage at the point of common coupling (PCC), or a DC storage at the DC link. Once the DC link is charged, a rotorside converter of one of the wind turbines is controlled in a manner to build voltage at a stator thereof, that is lower than a nominal voltage. The long transmission line(s) is then connected to the wind turbine to facilitate the passive energization of transformers via line capacitance. If the line capacitors are not sufficient to raise the voltage at the PCC and energize the transformers in the string, the wind turbine voltage is increased exponentially to energize the transformers, without any inrushcurrent. In addition, systems and methods of the present disclosure present optimized steps to connect a block load while the wind farm is operating in an islanding mode. Such steps are configured to ensure medized inrush current by the block load transformer.

[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 ofthe 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 1 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 withreference to the system 100 show n 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 show n, 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 rotor side converter 112. Additionally, the RSC 112 is coupled to the LSC 114 via a DC link 116 across which is a DC link capacitor 1 18. 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 betw een the power conversion assembly 106 and the turbine controller 26 and may include any number of control devices.

[0035] In ty pical 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 transformer130, 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 1 0 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 1 16. 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 show n, the wind farm 50 may include a plurality of wind turbines 52, including the wind turbine 10 described above, and anoverall 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 pow er 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 digitalversatile 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 double-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 powder system 200 may include a stator voltage regulator 206 for providing such gridforming characteristics. In addition, as shown, the grid forming power system 200may include a grid voltage / V AR regulator 202, an inertial power regulator 204, a rotor current regulator 208, and a modulator 210.

[0049] Referring now to FIGS. 8 and 9, the present disclosure is directed to a power generating farm 300 and method 400 of blackstarting the power generating farm 300 according to the present disclosure. In particular, FIG. 8 illustrates a schematic diagram of the power generating farm 300 according to the present disclosure, whereas FIG. 9 illustrates a flow diagram of an embodiment of a method 400 of blackstarting the power generating farm 300 according to the present disclosure.

[0050] Referring particularly to FIG. 8, in an embodiment, the power generating farm 300 includes a plurality of inverter-based resources 302. 304, 306 connected to a point of common connection (PCC) 308 via a respective transformer 310, 312, 314 (also referred to herein as a pad mount transformer) and a first switch 316, 318, 320. In an embodiment, one or more of the plurality' of inverter-based resources 302, 304, 306 are under grid forming control during the blackstarting. Accordingly, in particular embodiments, as shown, each of the inverter-based resources 302, 304, 306 may be 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, which contains the power conversion assembly 106 having the line-side converter 114 and the rotor-side converter 112 coupled together via the DC link 116. In addition, as shown, the wind turbine 10 includes the generator 102.

[0051] Further, as shown, the power generating farm 300 includes a power generating device 322. In particular embodiments, the power generating device 322 may be an anchor generator, such a diesel generator and / or an energy storage system. Moreover, as shown, in an embodiment, the power generating device 322 is connected yvith the PCC 308 via a second switch 324. In addition, the power generating farm 300 includes one or more transmission lines 326, one of which contains the PCC 308, for electrically connecting the various components of the power generating farm 300 to an electrical grid (not shown). Furthermore, as shown, the power generating farm 300 includes a third switch 328 connected between the PCC 308 and the electrical grid. Moreover, as show n, each of the respectivetransformers 310, 312, 314 is connected with the PCC 308 via a fourth switch 330, 332, 334.

[0052] Still referring to FIG. 8, the power generating farm 300 may further include a droop gain 336 and a filter 338. Thus, in an embodiment, the power generating farm 300 may receive a reactive current feedback that is filtered via the filter 338 and then the droop gain 336 can be applied to the filtered value. The output of the droop gain 336 can then be compared to a voltage reference (e.g., Volt Ref) to provide a voltage input value to the voltage regulator 202.

[0053] In general, the method 400 is described herein with reference to the wind turbine 10 and the wind farm 50 of FIGS. 2-7. 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. 9 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.

[0054] With the power generating farm 300 disconnected from the electrical grid, as shown at (402), the method 400 includes starting the power generating device 322 at a pre-defined voltage. As shown at (404), the method 400 includes energizing the respective transformers 310, 312, 314 connected to the PCC 308 at the pre-defined voltage. For example, in an embodiment, the respective transformers 310, 312, 314 may be energized by closing the second switch 324 (which connects the power generating device 322 to transmission hne 326) and the fourth switches 330, 332, 334 (if present). Moreover, in an embodiment, the method 400 may further include selectively operating the fourth switches 330, 332, 334 associated with the respective transformers 310, 312, 314 to facilitate selective energization of the respective transformers 310, 312. 314. More specifically, in an embodiment, selectively operating the fourth switches 330, 332, 334 associated with the respective transformers 310, 312, 314 may include energizing one or more of the respective transformers 310, 312, 314 through the power generating device 322 andsubsequently energizing the remaining of the respective transformers 310, 312, 314 using the power from the started wind turbine 302.

[0055] Referring still to FIG. 9, as shown at (406), the method 400 includes initiating the blackstarting of the power generating farm 300 by implementing a blackstart process of at least one inverter-based resource of the plurality of inverterbased resources (e.g., wind turbine 302). For example, in an embodiment, initiating the blackstarting of the power generating farm 300 by implementing the blackstart process of at least one inverter-based resource may include charging the DC link 116 of the power conversion assembly 106 and closing the first switch 316 associated with the inverter-based resource (e.g., wind turbine 302) to connect the wind turbine 302 with the respective transformer 310. In certain embodiments, the DC link 116 of the power conversion assembly 106 may be charged via the line-side converter 1 14 of the power conversion assembly 106, the power generating device 322, operating the PCC 308 at a lower voltage, and / or DC energy storage at the DC link of the power conversion assembly.

[0056] As shown at (408), the method 400 includes disconnecting the power generating device 322 from the PCC 308. For example, in an embodiment, disconnecting the power generating device 322 from the PCC 308 may include opening the second switch 324.

[0057] As shown at (410), the method 400 includes connecting the transmission line 326 with the PCC 308 to facilitate energization of the transmission line 326, e.g., through the inverter-based resource of the plurality of inverter-based resources (e.g., wind turbine 302). For example, in an embodiment, connecting the transmission line 326 with the PCC 308 may include closing the third switch 328 electrically connected between the PCC 308 and the electrical grid.

[0058] Further, in an embodiment, the method 400 includes ramping up an output voltage of the inverter-based resource connected to the PCC 308 to a nominal voltage value. More specifically, in an embodiment, as shown at (412). the method 400 includes determining whether the transmission line 326 is capacitive in nature. If yes, as shown at (416), the method 400 includes linearly increasing the droop gain 336 in the voltage regulator 202 of the inverter-based resource to gradually increase the output voltage of the inverter-based resource to the nominal voltage value in anexponential manner and to energize the transmission line 326. More specially, in an embodiment, gradually increasing the output voltage may include linearly increasing the droop gain 336.

[0059] If the transmission line 326 is not capacitive in nature, however, as shown at (414), the method 400 includes employing converter control, i.e., by increasing the voltage reference (e.g., Volt_Ref) of the voltage regulator 202 of the inverter-based resource (e.g., wind turbine 302) to a nominal voltage value, e.g.. to minimize inrush currents during energization of the power generating farm 300.

[0060] In certain embodiments, the pre-defined voltage is less than the nominal voltage value. Further, in an embodiment, the pre-defined voltage may range between 0.1 pu and 0.7 pu.

[0061] Referring now to FIG. 10, a schematic diagram of another embodiment of a power generating farm 500 according to the present disclosure is illustrated. FIG.10 is similar to the embodiment of FIG. 8 and thus like numbering is used to describe common components. In contrast to FIG. 8. however, the power generating device 322 is connected to the DC link 116 (rather than the transmission line 326) to support the blackstart process of the power generating farm 300. In such embodiments, the blackstart process may include starting the wind turbine 302 at a low voltage reference (e.g., Volt_Ref in FIGS. 8 and 10; typically less than 1 pu), closing the first switch 316 following synchronization, closing the fourth switches 330, 332, 334 (e.g., PMT hooks) if present, connecting the transmission line(s) 326, and ramping up the voltage reference signal to 1 pu with an optimized ramp-up slope (if voltage has not already increased).

[0062] Further aspects of the invention are provided by the subject matter of the following clauses:

[0063] A method of blackstarting a power generating farm having a plurality of inverter-based resources and a power generating device, each of the plurality' of inverter-based resources connected to a point of common connection (PCC) via a respective transformer and a first switch, the method comprising: with the power generating farm disconnected from an electrical grid, starting the power generating device at a pre-defined voltage; energizing the respective transformers connected to the PCC at the pre-defined voltage; initiating the blackstarting of the powergenerating farm by implementing a blackstart process of at least one inverter-based resource of the plurality of inverter-based resources; disconnecting the power generating device from the PCC; connecting a transmission line having the PCC to the electrical grid to facilitate energization of the transmission line through the at least one inverter-based resource of the plurality7of inverter-based resources; and ramping up an output voltage of the at least one inverter-based resource to a nominal voltage value.

[0064] The method of any preceding clause, wherein one or more of the plurality of inverter-based resources are under grid forming control during the blackstarting.

[0065] The method of any preceding clause, wherein the power generating device is connected with the PCC via a second switch, and wherein energizing the respective transformers connected to the PCC at the pre-defined voltage further comprises closing the second switch to facilitate energization of the respective transformers connected to the PCC at the pre-defined voltage.

[0066] The method of any preceding clause, wherein disconnecting the power generating device from the PCC further comprises opening the second switch.

[0067] The method of any preceding clause, wherein initiating the blackstarting of the power generating farm by implementing the blackstart process of at least one inverter-based resource of the plurality' of inverter-based resources further comprises: charging a DC link of the power conversion assembly of the at least one inverterbased resource; and closing the first switch associated with the at least one inverterbased resource to connect the at least one inverter-based resource with the respective transformer.

[0068] The method of any preceding clause, further comprising charging the DC link of the power conversion assembly of the at least one inverter-based resource via at least one of a line-side converter of the power conversion assembly, the power generating device, operating the PCC at a lower voltage, or DC energy storage at the DC link of the power conversion assembly.

[0069] The method of any preceding clause, wherein connecting the transmission line with the PCC to the electrical grid further comprises closing a third switch electrically connected between the PCC and the electrical grid.

[0070] The method of any preceding clause, wherein each of the respectivetransformers is connected with the PCC via a fourth switch, the method further comprising selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers.

[0071] The method of any preceding clause, wherein selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers further comprises: energizing one or more of the respective transformers using power from the power generating device; and subsequently energizing the remaining of the respective transformers through the at least one inverter-based resource.

[0072] The method of any preceding clause, wherein the plurality of inverterbased resources is a plurality of wind turbines.

[0073] The method of any preceding clause, wherein ramping up the output voltage of the at least one inverter-based resource connected to the PCC to the nominal voltage value further comprises: determining if the transmission line is capacitive in nature; when the transmission line is capacitive in nature, gradually increasing the output voltage of the at least one inverter based resource; and when the transmission line is not capacitive in nature, increasing the output voltage by employing converter control of the at least one inverter based resource.

[0074] The method of any preceding clause, wherein gradually increasing the output voltage further comprises linearly increasing a droop gain in a voltage regulator loop of a converter control of the at least one inverter based resource, and wherein increasing the output voltage by employing the converter control further comprises increasing a voltage reference of a converter controller of the at least one inverter based resource.

[0075] The method of any preceding clause, wherein the pre-defined voltage is less than the nominal voltage value.

[0076] The method of any preceding clause, wherein the pre-defined voltage ranges between 0. 1 pu and 0.7 pu.

[0077] The method of any preceding clause, wherein the power generating device comprises at least one of an energy storage system or a diesel generator.

[0078] A wind farm, comprising: a main transformer; a plurality of local transformers; a plurality of local switches; a plurality7of wind turbines, each of theplurality of wind turbines connected to a point of common connection (PCC) via a respective transformer of the plurality of local transformers and a first switch of the plurality of local switches; a power generating device; and a controller comprising at least one processor, the at least one processor configured to perform a plurality of operations, the plurality7of operations comprising: with the wind farm disconnected from an electrical grid, starting the power generating device at a pre-defined voltage; energizing the respective transformers connected to the PCC at the pre-defined voltage; implementing a blackstart process of at least one wind turbine of the plurality of wind turbines, the at least one wind turbine being under grid forming control; disconnecting the power generating device from the PCC; connecting a transmission line having the PCC to the electrical grid to facilitate energization of the transmission line through the at least one wind turbine of the plurality of wind turbines; and ramping up an output voltage of the at least one wind turbine to a nominal voltage value.

[0079] The wind farm of any preceding clause, wherein the power generating device is connected with the PCC via a second switch, wherein energizing the respective transformers connected to the PCC at the pre-defined voltage further comprises closing the second switch to facilitate energization of the respective transformers connected to the PCC at the pre-defined voltage, and wherein disconnecting the power generating device from the PCC further comprises opening the second switch.

[0080] The wind farm of any preceding clause, wherein implementing the blackstart process of at least one wind turbine of the plurality of wind turbines further comprises: charging a DC link of the power conversion assembly of the at least one wind turbine via at least one of a line-side converter of the power conversion assembly, the power generating device, operating the PCC at a lower voltage, or DC energy storage at the DC link of the power conversion assembly; and closing the first switch associated with the at least one wind turbine to connect the at least one wind turbine with the respective transformer.

[0081] The wind farm of any preceding clause, wherein connecting the transmission line with the PCC to the electrical grid further comprises closing a third switch electrically connected between the PCC and the electrical grid, and whereineach of the respective transformers is connected with the PCC via a fourth switch, the plurality of operations further comprising: selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers, wherein selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers further comprises: energizing one or more of the respective transformers using power from the power generating device; and subsequently energizing the remaining of the respective transformers through the at least one started wind turbine.

[0082] The wind farm of any preceding clause, wherein ramping up the output voltage of the at least one wind turbine to the nominal voltage value further comprises: determining if the transmission line is capacitive in nature; when the transmission line is capacitive in nature, gradually increasing the output voltage of the at least one wind turbine, wherein gradually increasing the output voltage further comprises linearly increasing a droop gain in a voltage regulator loop of a converter control of the at least one wind turbine; and when the transmission line is not capacitive in nature, increasing the output voltage by employing converter control of the at least one wind turbine, wherein increasing the output voltage by employing the converter control further comprises increasing a voltage reference of a converter controller of the at least one wind turbine.

[0083] 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

WHAT IS CLAIMED IS:

1. A method of blackstarting a power generating farm having a plurality of inverter-based resources and a power generating device, each of the plurality of inverter-based resources connected to a point of common connection (PCC) via a respective transformer and a first switch, the method comprising: with the power generating farm disconnected from an electrical grid, starting the power generating device at a pre-defined voltage; energizing the respective transformers connected to the PCC at the pre-defined voltage; initiating the blackstarting of the power generating farm by implementing a blackstart process of at least one inverter-based resource of the plurality of inverterbased resources; disconnecting the power generating device from the PCC; connecting a transmission line having the PCC to the electrical grid to facilitate energization of the transmission line through the at least one inverter-based resource of the plurality of inverter-based resources; and ramping up an output voltage of the at least one inverter-based resource to a nominal voltage value.

2. The method of claim 1 , wherein one or more of the plurality of inverter-based resources are under grid forming control during the blackstarting.

3. The method of claim 1, wherein the power generating device is connected with the PCC via a second switch, and wherein energizing the respective transformers connected to the PCC at the pre-defined voltage further comprises closing the second switch to facilitate energization of the respective transformers connected to the PCC at the pre-defined voltage.

4. The method of claim 3, wherein disconnecting the power generating device from the PCC further comprises opening the second switch.

5. The method of claim 1, wherein initiating the blackstarting of the power generating farm by implementing the blackstart process of at least one inverterbased resource of the plurality of inverter-based resources further comprises: charging a DC link of the power conversion assembly of the at least one inverter-based resource; andclosing the first switch associated with the at least one inverter-based resource to connect the at least one inverter-based resource with the respective transformer.

6. The method of claim 5. further comprising charging the DC link of the power conversion assembly of the at least one inverter-based resource via at least one of a line-side converter of the power conversion assembly, the power generating device, operating the PCC at a lower voltage, or DC energy storage at the DC link of the power conversion assembly.

7. The method of claim 1, wherein connecting the transmission line with the PCC to the electrical grid further comprises closing a third switch electrically connected between the PCC and the electrical grid.

8. The method of claim 1. wherein each of the respective transformers is connected with the PCC via a fourth switch, the method further comprising selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers.

9. The method of claim 8, wherein selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers further comprises: energizing one or more of the respective transformers using power from the power generating device; and subsequently energizing the remaining of the respective transformers through the at least one inverter-based resource.

10. The method of claim 1, wherein the plurality of inverter-based resources is a plurality of wind turbines.

11. The method of claim 10, wherein ramping up the output voltage of the at least one inverter-based resource connected to the PCC to the nominal voltage value further comprises: determining if the transmission line is capacitive in nature; when the transmission line is capacitive in nature, gradually increasing the output voltage of the at least one inverter based resource; and when the transmission line is not capacitive in nature, increasing the output voltage by employing converter control of the at least one inverter based resource.

12. The method of claim 11, wherein gradually increasing the outputvoltage further comprises linearly increasing a droop gain in a voltage regulator loop of a converter control of the at least one inverter based resource, and wherein increasing the output voltage by employing the converter control further comprises increasing a voltage reference of a converter controller of the at least one inverter based resource.

13. The method of claim 11, wherein the pre-defined voltage is less than the nominal voltage value.

14. The method of claim 1, wherein the pre-defined voltage ranges between 0.1 pu and 0.7 pu.

15. The method of claim 1, wherein the power generating device comprises at least one of an energy storage system or a diesel generator.

16. A wind farm, comprising: a main transformer; a plurality of local transformers; a plurality of local switches; a plurality of wind turbines, each of the plurality of wind turbines connected to a point of common connection (PCC) via a respective transformer of the plurality of local transformers and a first switch of the plurality of local switches; a power generating device; and a controller comprising at least one processor, the at least one processor configured to perform a plurality of operations, the plurality of operations comprising: with the wind farm disconnected from an electrical grid, starting the pow er generating device at a pre-defined voltage; energizing the respective transformers connected to the PCC at the predefined voltage; implementing a blackstart process of at least one wind turbine of the plurality of wind turbines, the at least one wind turbine being under grid forming control; disconnecting the power generating device from the PCC; connecting a transmission line having the PCC to the electrical grid to facilitate energization of the transmission line through the at least one wind turbine of the plurality of wind turbines; andramping up an output voltage of the at least one wind turbine to a nominal voltage value.

17. The wind farm of claim 16. wherein the power generating device is connected with the PCC via a second switch, wherein energizing the respective transformers connected to the PCC at the pre-defined voltage further comprises closing the second switch to facilitate energization of the respective transformers connected to the PCC at the pre-defined voltage, and wherein disconnecting the power generating device from the PCC further comprises opening the second switch.

18. The wind farm of claim 16, wherein implementing the blackstart process of at least one wind turbine of the plurality of wind turbines further comprises: charging a DC link of the power conversion assembly of the at least one wind turbine via at least one of a line-side converter of the power conversion assembly, the power generating device, operating the PCC at a lower voltage, or DC energy' storage at the DC link of the power conversion assembly; and closing the first switch associated with the at least one wind turbine to connect the at least one wind turbine with the respective transformer.

19. The wind farm of claim 18, wherein connecting the transmission line with the PCC to the electrical grid further comprises closing a third switch electrically connected between the PCC and the electrical grid, and wherein each of the respective transformers is connected with the PCC via a fourth switch, the plurality of operations further comprising: selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers, wherein selectively operating the fourth switches associated with the respective transformers to facilitate selective energization of the respective transformers further comprises: energizing one or more of the respective transformers using pow er from the power generating device; and subsequently energizing the remaining of the respective transformers using the powder from the at least one started wind turbine.

20. The wind farm of claim 19, wherein ramping up the output voltage ofthe at least one wind turbine to the nominal voltage value further comprises: determining if the transmission line is capacitive in nature; when the transmission line is capacitive in nature, gradually increasing the output voltage of the at least one wind turbine, wherein gradually increasing the output voltage further comprises linearly increasing a droop gain in a voltage regulator loop of a converter control of the at least one wind turbine; and when the transmission line is not capacitive in nature, increasing the output voltage by employing converter control of the at least one wind turbine, wherein increasing the output voltage by employing the converter control further comprises increasing a voltage reference of a converter controller of the at least one wind turbine.

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