WO2025063949A1

WO2025063949A1 - System and method for providing blackstart services from inverter-based resources

Info

Publication number: WO2025063949A1
Application number: PCT/US2023/033235
Authority: WO
Inventors: Dustin F. HOWARD; Ignacio Vieto Miranda; Cornelius Edward Holliday III
Original assignee: GE Infrastructure Technology LLC
Current assignee: GE Vernova Infrastructure Technology LLC
Priority date: 2023-09-20
Filing date: 2023-09-20
Publication date: 2025-03-27
Anticipated expiration: 2026-03-20

Abstract

A method of blackstarting a power generating farm includes sending a blackstart command to one or more first inverter-based resources having energy storage on an isolated first feeder at the power generating farm. Thus, the method includes implementing a blackstart mode using the first inverter-based resource(s) having the energy storage, which includes using a first converter of the first inverter-based resource(s) with the energy storage to establish an auxiliary voltage and an auxiliary frequency to one or more auxiliary loads thereof and using a second converter of the first inverter-based resource(s) with the energy storage to establish a first voltage and a first frequency to the isolated first feeder. The method also includes energizing one or more first inverter-based resources without blackstart capability via the isolated first feeder, switching from the blackstart mode to a normal mode, and connecting the power generating farm to the electrical grid.

Description

SYSTEM AND METHOD FOR PROVIDING BLACKSTART SERVICES FROM INVERTER-BASED RESOURCES

FIELD

[0001] The present disclosure relates generally to wind turbines and, more particularly, to systems and methods for providing blackstart sendees from inverterbased 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 are located in a weak grid, wind turbine power fluctuations may lead to an increase in magnitude and frequency variations in the grid voltage.

[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 load characteristic, including serving an isolated load or connected with other grid-forming sources, and switching between such configurations; (4) share total load of the grid among other grid-forming sources connected to the grid; (5) ride through grid disturbances, both major and minor, and (6) meet requirements (1 )-(5) without requiring fast communication with other control systems existing in the grid, or externally-created logic signals related to grid configuration changes.

[0006] The basic control structure to achieve the above grid-forming objectives was developed and field-proven for battery' systems in the early 1990’s (see e.g., United States Patent No.: 5,798,633 entitled “Battery Energy Storage Power Conditioning System”). Applications to full-converter wind generators and solar generators are disclosed in United States Publication No.: 2010/0142237 entitled “System and Method for Control of a Grid Connected Pow er 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 capability⁷ of a conventional generator is an important element in grid restoration following a blackout. Existing wind farms require an operating grid voltage or other external alternating current (AC) power source to operate auxiliary loads and to startup. Other types of generators, such as conventional thermal or gas turbine generators, have historically been used to blackstart the grid in case of 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 services from inverter-based resources, such as wind turbines.

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 pow er generating farm. The method includes, with the power generating farm disconnected from an electrical grid, sending, via a controller, a blackstart command to one or more first inverter-based resources on an isolated first feeder at the power generating farm, the one or more first inverter-based resources having energy storage. Upon receipt of the blackstart command, the method includes implementing a blackstart mode using the one or more first inverter-based resources having the energy storage. Implementing the blackstart mode includes using a first converter of the one or more first inverter-based resources with the energy storage to establish an auxiliary voltage and an auxiliary frequency to one or more auxiliary loads thereof and using a second converter of the one or more first inverter-based resources with the energy storage to establish a first voltage and a first frequency to the isolated first feeder. The method also includes energizing one or more first inverter-based resources without blackstart capability via the isolated first feeder. Further, the method includes switching from the blackstart mode to a normal mode. Moreover, the method includes connecting the power generating farm to the electrical grid to support the blackstarting or restoration of portions of the electrical grid.

[0011] In another aspect, the present disclosure is directed to a wind farm. The w ind farm includes a plurality of wind turbines capable of being connected to an electrical grid via a transmission network and a controller having at least one processor. The processor(s) is configured to perform a plurality of operations, including with the wind farm disconnected from the electrical grid, sending a blackstart command to one or more first wind turbines on an isolated first feeder at the wind farm, the one or more first wind turbines having energy storage; upon receipt of the blackstart command, implementing a blackstart mode using the one or more first wind turbines having the energy storage to establish a voltage and a frequency on the isolated first feeder, wherein implementing the blackstart mode comprises using a first converter of the one or more first inverter-based resources with the energy storage to establish an auxiliary voltage and an auxiliary' frequency to one or more auxiliary loads thereof and using a second converter of the one or more first inverterbased resources with the energy storage to establish a first voltage and a first frequency to the isolated first feeder; energizing one or more first inverter-based resources without blackstart capability⁷ via the isolated first feeder; switching from the blackstart mode to a normal mode; and connecting the power generating farm to the electrical grid to support the blackstarting or restoration of portions of the electrical grid.

[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 draw ings, 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 wand 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 w ith converter controls for grid-forming application according to the present disclosure;

[0021] FIG. 8 illustrates a flow diagram of an embodiment of a method of blackstarting a power generating farm connected to an electrical grid according to the present disclosure;

[0022] FIG. 9 illustrates a schematic diagram of an embodiment of a system of blackstarting a power generating farm connected to an electrical grid according to the present disclosure;

[0023] FIG. 10 illustrates a schematic diagram of an embodiment of a gridforming wind turbine having energy storage according to the present disclosure; and [0024] FIG. 11 illustrates a schematic diagram of an embodiment of a control structure of a grid-forming wind turbine having energy' storage according to the present disclosure.

DETAILED DESCRIPTION

[0025] 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. [0026] Increasing levels of renewable integration is linked to increasing costs of grid security. As such, emerging grid codes require inverter-based resources to provide functionality that have been traditionally provided by synchronous generators. An example of such functionality is for the generation resource to provide blackstart capability'. In view of the foregoing, the present disclosure is directed to systems and methods for providing blackstart of a power generating farm connected to an electrical grid. In an embodiment, for example, the method of the present disclosure involves a blackstarting wind turbine that does not rely on external AC power source. In particular, embodiments, the first blackstarting wind turbine (or group of wind turbines) with this capability is further used to start other wind turbines within the power generating farm, followed by energizing parts of the external electrical grid to facilitate blackstarting the electrical grid.

[0027] Referring now to the drawings, FIG. 2 illustrates a perspective view of one embodiment of a wind turbine 10 according to the present disclosure. As shown, the wind turbine 10 generally includes a tower 12 extending from a support surface 14, a nacelle 16 mounted on the tower 12. and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in an alternative embodiment, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy'. For instance, the hub 20 may be rotatably coupled to an electric generator 24 (FIG. 3) positioned within the nacelle 16 to permit electrical energy to be produced.

[0028] The wind turbine 10 may also include a wind turbine controller 26 centralized within the nacelle 16. However, in other embodiments, the controller 26 may be located within any other component of the wind turbine 10 or at a location outside the wind turbine 10. Further, the controller 26 may be communicatively coupled to any number of the components of the wind turbine 10 in order to control the operation of such components and/or implement a corrective or control action. As such, the controller 26 may include a computer or other suitable processing unit. Thus, in several embodiments, the controller 26 may include suitable computer- readable instructions that, when implemented, configure the controller 26 to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals. Accordingly, the controller 26 may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences), de-rating or up-rating the wind turbine, and/or individual components of the wind turbine 10.

[0029] Referring now to FIG. 2, a simplified, internal view of one embodiment of the nacelle 16 of the wind turbine 10 shown in FIG. 1 is illustrated. As shown, a generator 24 may be disposed within the nacelle 16 and supported atop a bedplate 46. In general, the generator 24 may be coupled to the rotor 18 for producing electrical power from the rotational energy generated by the rotor 18. For example, as shown in the illustrated embodiment, the rotor 18 may include a rotor shaft 34 coupled to the hub 20 for rotation therewith. The rotor shaft 34 may, in turn, be rotatably coupled to a generator shaft 36 of the generator 24 through a gearbox 38. As is generally understood, the rotor shaft 34 may provide a low speed, high torque input to the gearbox 38 in response to rotation of the rotor blades 22 and the hub 20. The gearbox 38 may then be configured to convert the low speed, high torque input to a high speed, low torque output to drive the generator shaft 36 and, thus, the generator 24. [0030] The wind turbine 10 may also one or more pitch drive mechanisms 32 communicatively coupled to the wind turbine controller 26, with each pitch adjustment mechanism(s) 32 being configured to rotate a pitch bearing 40 and thus the individual rotor blade(s) 22 about its respective pitch axis 28. In addition, as shown, the wind turbine 10 may include one or more yaw' drive mechanisms 42 configured to change the angle of the nacelle 16 relative to the wind (e.g., byengaging 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. Still further sensors 68 may be utilized to measure additional operating parameters of the wind turbine 10, such as voltage, current, vibration, etc. as described herein. [0032] Referring now to FIG. 4, a schematic diagram of one embodiment of a wind turbine power system 100 is illustrated in accordance with aspects of the present disclosure. Although the present disclosure will generally be described herein with reference to the system 100 shown in FIG. 4, those of ordinary skill in the art, using the disclosures provided herein, should understand that aspects of the present disclosure may also be applicable in other power generation systems, and, as mentioned above, that the invention is not limited to wind turbine systems.

[0033] In the embodiment of FIG. 4 and as mentioned, the rotor 18 of the wind turbine 10 (FIG. 2) may, optionally, be coupled to the gearbox 38, which is, in turn, coupled to a generator 102, which may be a doubly fed induction generator (DFIG). As shown, the GENERATOR 102 may be connected to a stator bus 104. Further, as shown, a power converter 106 may be connected to the GENERATOR 102 via a rotor bus 108, and to the stator bus 104 via a line side bus 1 10. 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 converter 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 118. The LSC 114 is, in turn, coupled to the line side bus 110.

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

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

[0036] In operation, alternating current power generated at the GENERATOR 102 by rotating the rotor 18 is provided to the electrical grid 124 via dual paths defined by the stator bus 104 and the rotor bus 108. On the rotor bus side 108, sinusoidal multiphase (e.g., three-phase) alternating current (AC) power is provided to the power converter 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 converter 106 can be combined with the power from the stator of GENERATOR 102 to provide multi-phase power (e.g., three-phase power) having a frequency maintained substantially at the frequency of the electrical grid 124 (e.g., 50 Hz or 60 Hz).

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

[0039] Moreover, the power converter 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 converter 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 converter 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 converter 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 frequency is substantially independent of the mechanical rotor speed.

[0041] Under some states, the bi-directional characteristics of the power converter 106, and specifically, the bi-directional characteristics of the LSC 1 14 and RSC 112, facilitate feeding back at least some of the generated electrical power into the 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 converter 106, specifically the LSC 114 which acts as a rectifier and rectifies the sinusoidal, three-phase AC power to DC power. The DC power is transmitted into the DC link 116. The capacitor 118 facilitates mitigating DC link voltage amplitude variations by facilitating mitigation of a DC ripple sometimes associated with three-phase AC rectification.

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

[0043] Referring now to FIG. 5, the wind turbine power system 100 described herein may be part of a wind farm 50. As shown, the wind farm 50 may include a plurality of wind turbines 52, including the wind turbine 10 described above, and an overall farm-level controller 56. For example, as shown in the illustrated embodiment, the wind farm 50 includes twelve wind turbines, including wind turbine 10. However, in other embodiments, the wind farm 50 may include any other number of wind turbines, such as less than twelve wind turbines or greater than twelve wind turbines. In one embodiment, the turbine controllers of the plurality of w ind turbines 52 are communicatively coupled to the farm-level controller 56, e.g., through a wired connection, such as by connecting the turbine controller 26 through suitable communicative links 54 (e.g., a suitable cable). Alternatively, the turbine controllers may be communicatively coupled to the farm-level controller 56 through a wireless connection, such as by using any suitable wireless communications protocol known in the art. In further embodiments, the farm-level controller 56 is configured to send and receive control signals to and from the various wind turbines 52, such as for example, distributing real and/or reactive power demands or voltage reference commands 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 memory⁷ 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 memory⁷ device(s) 60 may generally comprise memory⁷ element(s) including, but not limited to, computer readable medium (e.g., random access memory⁷ (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements.

[0046] Such memory device(s) 60 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 58. configure the controller to perform various functions as described herein. Additionally, the controller may also include a communications interface 62 to facilitate communications between the controller and the various components of the wind turbine 10. An interface can include one or more circuits, terminals, pins, contacts, conductors, or other components for sending and receiving control signals. Moreover, the controller may include a sensor interface 64 (e.g., one or more analog- to-digital converters) to permit signals transmitted from the sensors 66, 68 to be converted into signals that can be understood and processed by the processor(s) 58. [0047] Referring now to FIG. 7, a schematic diagram of an embodiment of a grid forming power system 200 according to the present disclosure, particularly illustrating a one-line diagram of the generator 102 with a high-level control structure for gridforming 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 show n in FIG. 1. More particularly, as shown, the line side converter control structure may include a DC regulator 212 and a line current regulator 214. The DC regulator 212 is configured to generate line-side current commands for the line current regulator 214. The line current regulator 214 then generates line-side voltage commands for a modulator 218. The modulator 218 also receives an output (e.g., a phase-locked loop angle) from a phase-locked loop 216 to generate one or more gate pulses for the line side converter 114. The phase-locked loop 216 typically generates its output using a voltage feedback signal.

[0048] Furthermore, as shown, the grid forming power system 200 may also include a unique control structure for controlling the rotor side converter 112 using grid-forming characteristics. In particular, as shown in FIG. 7, the grid forming power system 200 may include a stator voltage regulator 206 for providing such gridforming characteristics. In addition, as shown, the grid forming power system 200 may include a grid voltage/V AR regulator 202, an inertial pow er 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 to convert voltage commands from the grid-forming controls to rotor current regulator commands. Thus, the system and method of the present disclosure provide control of the rotor voltage of the generator 102 to meet a higher-level command for magnitude and angle of stator voltage. Such control must be relatively fast and insensitive to current flowing in the stator of the generator 102.

[0050] Referring now to FIGS. 8 and 9, the present disclosure is directed to a method 250 and system 300 for blackstarting a power generating farm, such as the wind farm 50, connected to an electrical grid according to the present disclosure. In particular, FIG. 8 illustrates a flow diagram of an embodiment of the method 250 for blackstarting a power generating farm, such as the wind farm 50, connected to an electrical grid according to the present disclosure, whereas FIG. 9 illustrates a schematic diagram of an embodiment of the system 300 for blackstarting a power generating farm, such as the wind farm 50, connected to an electrical grid according to the present disclosure. In general, the method 250 and system 300 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 250 and system 300 may be implemented with any inverter-based resources in addition to wind turbines having any other suitable configurations. In addition, although FIG. 8 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. [0051] As shown at (252) in FIG. 8, the method 250 includes disconnecting the power generating farm (e.g., the wind farm 50) from the electrical grid following a blackout. For example, in an embodiment, as shown in FIG. 9, the wind farm 50 may be disconnected from the electncal grid by opening a plurality of switchgears 302 to a plurality of feeders 304 and a main switchgear 306 to a transformer 308 of the wind farm 50.

[0052] Moreover, and referring back to FIG. 8, the method 250 includes setting an inertial power regulator reference to zero, the frequency to a baseline frequency reference, and the voltage to a baseline voltage reference. In such embodiments, the baseline voltage reference is less than or equal to a nominal voltage and the baseline frequency reference is less than or equal to a nominal frequency. [0053] With the power generating farm (e.g., the wind farm 50) disconnected from the electrical grid, as shown at (254), the method 250 includes sending, via a controller, a blackstart command to one or more first inverter-based resources (e.g., wind turbines) on an isolated first feeder at the power generating farm. In such embodiments, the first inverter-based resource (s) have energy storage and grid forming capability. For example, as shown in FIG. 9, the wind farm 50 includes an isolated first feeder 310 having one or more grid forming wind turbines 312 with energy storage 324 (FIG. 10), only one of which is shown for clarity. In an embodiment, for example, the number of grid forming wind turbines 312 with energy storage may be dependent upon the individual feeder and/or auxiliary loads on the first feeder 310.

[0054] Referring back to FIG. 8, upon receipt of the blackstart command, as shown at (256), the method 250 includes implementing a blackstart mode using the one or more first inverter-based resources (e.g., the grid forming wind turbine(s) 312) having the energy’ storage. For example, upon receipt of the blackstart command, the grid forming wind turbine(s) 312 begin energizing equipment in the blackstart mode. [0055] More specifically, in an embodiment, implementing the blackstart mode may include using a first converter of the one or more first inverter-based resources with the energy storage to establish an auxiliary voltage and an auxiliary frequency to one or more auxiliary’ loads thereof and using a second converter of the one or more first inverter-based resources with the energy storage to establish a first voltage, that folloyvs the baseline voltage reference, and a first frequency, that folloyvs the baseline frequency reference, to the isolated first feeder. Further, in an embodiment, implementing the blackstart mode may include ramping up the voltage of the first inverter-based resource(s) having the energy storage at a predetermined rate to a first voltage reference yvith a first frequency reference. In such embodiments, the predetermined rate and reduced voltage/frequency is configured to reduce transient and steady-state loading during the blackstart mode.

[0056] Moreover, in an embodiment, as shown in FIG. 10, ramping up the voltage of the first inverter-based resource(s) (e.g., the grid forming wind turbine(s) 312) having the energy storage 324 at the predetermined rate to the first voltage reference with the first frequency reference may include using energy from at least one of the energy storage 324 and/or one or more first converters 326 (such as a RSC) of the grid forming wind turbine(s) 312 to facilitate the blackstarting of the wind farm 50. Further, as shown in FIG. 10, ramping up the voltage of the grid forming wind turbine(s) 312 at the predetermined rate to the first voltage reference with the first frequency reference may include supplying auxiliary power 330 by at least one of the energy storage 324 and/or one or more second converters 328 (such as a LSC) of the grid forming wind turbine(s) 312. In such embodiments, the auxiliary power 330 is configured to supply at least one of auxiliary' loads, cable charging, or losses of the grid forming wind turbine(s) 312.

[0057] Accordingly, in an embodiment, as shown in FIG. 10, the blackstart mode may generally include charging a DC bus 334 and enabling control cards 332 via the energy storage 324. Further, as shown, the blackstart mode generally includes closing and opening a plurality⁷ of switches (e.g., SI, S2, S3, S4, S5, and S6) according the desired blackstart mode. Moreover, the blackstart mode generally includes running either the LSC 328 or the RSC 326 according to desired blackstart mode to provide the auxiliary power 330 to the auxiliary loads. With the other of the converters (i.e., the converter not supplying the auxiliary⁷ loads) is operating in a black start mode, where the blackstart mode may generally also include using grid forming control and the ramp voltage to energize a transformer 336, collector cable, and/or one or more other unit on the first feeder 310.

[0058] Moreover, and still referring to FIG. 10, the various dotted boxes illustrate when the plurality of switches (e.g., SI, S2, S3, S4, S5, and S6) are opened and closed. In particular, as shown, switches SI and S2 are closed during the normal mode and closed if blackstarting the electrical grid with a RSC 326 from the grid forming wind turbine(s) 312 with the energy storage 324. Further, as shown, switch S3 is closed during the normal mode, closed if blackstarting the electrical grid using only the energy⁷ storage 324 and a LSC 328, and closed when energizing the auxiliary' loads and the DC bus 334 during normal startup. Moreover, as shown, switch S4 is closed during the normal mode, closed if blackstarting the electrical grid using only the energy storage 324 and one of the converters, closed when energizing the auxiliary loads and the DC bus 334 during normal startup, and closed if blackstarting the electrical grid from the grid forming wind turbine(s) 312 with the energy storage 324. In addition, as shown, switch S5 is closed during the normal mode, closed when energizing the auxiliary loads and the DC bus 334 during normal startup, and closed if blackstarting the electrical grid from the RSC 326 of the grid forming wind turbine(s) 312 with the energy storage 324. Further, as shown, switch S6 is closed if blackstarting the electrical grid using only the energy storage 324 and the LSC 328. [0059] Referring back to FIG. 8, as shown at (258), the method 250 includes energizing one or more first inverter-based resources without blackstart capability via the isolated first feeder. For example, as show n in FIG. 9, the wind farm 50 includes one or more wind turbines 314 on the isolated first feeder 310 without blackstart capability. Thus, after the grid forming wind turbine(s) 312 are energized, the grid forming wind turbine(s) 312 begin energizing the wind turbine(s) 314 on the isolated first feeder 310 without blackstart capability. In another embodiment, the wind turbine(s) 314 on the isolated first feeder 310 without blackstart capability, as indicated by dotted boxes 322, may be designed with a medium-voltage (MV) switchgear and/or auxiliary load isolation to reduce loading upon blackstarting the wind turbine(s) 314. In certain embodiments, the wind turbine(s) 314 on the isolated first feeder 3120 without blackstart capability may either be grid-following wind turbine(s) or grid-forming wind turbine(s).

[0060] Referring back to FIG. 8, as shown at (260), the method 250 includes energizing the isolated first feeder. For example, in an embodiment, as shown in FIG. 9, energizing the isolated first feeder 310 may include closing one or more switchgears (such as switchgear 302) to energize a collector bus 316 of the isolated first feeder 310.

[0061] Referring back to FIG. 8. as shown at (262), the method 250 includes energizing one or more second feeders having one or more second inverter-based resources via the isolated first feeder. For example, as shown in FIG. 9, once the first feeder 310 is energized, the switchgear 302 of one or more second feeders 318 can be closed and the first feeder 310 can be used to energize the second feeder(s) 318 having a plurality’ of second wind turbines 320, e.g.. without blackstart capability. As such, the cables, pad mounts, etc. on the second feeder(s) 318 can be energized via the first feeder 310.

[0062] Thus, and referring back to FIG. 8, as shown at (264), the method 250 includes sequentially starting the one or more second inverter-based resources, e.g., the plurality of second wind turbines 320. For example, in an embodiment, the plurality of second wind turbines 320 may be without blackstart capability. Thus, in an embodiment, sequentially starting the second inverter-based resource(s) may include sequentially starting the second inverter-based resource(s) without blackstart capability.

[0063] Moreover, in an embodiment, such steps can be repeated as needed for any number of feeders. As shown at (266), the method 250 includes switching from the blackstart mode to a normal mode. For example, in an embodiment, switching from the blackstart mode to the normal mode may include sending a signal to the grid forming wind turbine(s) 312 to operate in the normal mode. In particular, as shown in FIG. 10, transferring from the blackstart mode to the normal mode may include synchronizing temporary auxiliary supply with grid voltage, and closing the necessary switches (e g., any of SI, S2, S3, S4, S5, and S6) to run the auxiliary loads off an external AC supply (not shown) and/or from the power generated by the grid forming wind turbine(s) 312. Further, in an embodiment, transferring from the blackstart mode to the normal mode may include disconnecting the temporary connection from the RSC 326 or the LSC 328 to the auxiliary loads (if necessary) and transferring the controls of either the RSC 326 or the LSC 328 that was previously supplying the auxiliary power to the normal mode of control.

[0064] In addition, after switching to the normal mode, as show n at (268) of FIG. 8, the method 250 may include increasing the first voltage reference and the first frequency reference to a second voltage reference and a second frequency reference, respectively. Furthermore, in an embodiment, as shown at (270), the method 250 includes energizing the power generating farm before connecting the power generating farm to the electrical grid. Moreover, as shown at (272), the method 250 includes connecting the power generating farm, e.g., the wind farm 50, to the electrical grid to support the blackstarting or restoration of portions of the electrical grid.

[0065] Referring now to FIG. 11, a schematic diagram of an embodiment of a control structure 400 of the grid forming wind turbine 312 with the energy storage 324 is illustrated. In particular, as shown, converter controls 402 utilize GFM controls for normal operation and for blackstart operation. Furthermore, simple voltage/frequency controls may be used to temporarily control one of the bridges during the blackstart mode to supply the auxiliary loads. The desired operating mode 406 determines which control drives which bridge voltage. The desired operating mode may be determined based on the available wind at the turbine, the state of charge of the energy storage, or combinations of the two.

[0066] Moreover, in an embodiment, blackstarting can be implemented using the LSC 328 only (with the RSC 326 feeding the auxiliary loads). Further, a grid voltage/VAR regulator 408 and an inertial power regulator 410 drive voltage command 412 of the LSC 328 together with PLL angle 414 (e.g., OPLL). Thus, in an embodiment, the LSC 328 is operating as a grid-forming converter to blackstart the first feeder. In addition, as shown, an auxiliary voltage control 416 drives voltage command 418 using a nominal frequency/angle signal 420 (e.g., Onom). Further, as show n, battery control 422 regulates a DC voltage of a DC link 424.

[0067] In another embodiment, blackstarting can be implemented using the RSC 326 only (with the LSC 328 feeding the auxiliary loads). In such embodiments, the grid voltage/VAR regulator 408 and the inertial power regulator 410 drive the voltage command 418 of the RSC 326 through a stator voltage regulator 426 and a rotor current regulator 428 together with the PLL angle 414 (e.g., OPLL) and rotor position feedback 430 (e.g.. Oriri,). Thus, in this embodiment, the RSC 328 facilitates the gridforming function needed for blackstarting. In addition, as shown, the auxiliary voltage control 416 drives voltage command 412 together with the nominal frequency/angle signal 420 (e.g., Onom). In addition, the battery control 422 regulates the DC voltage of the DC link 424. Further, in such embodiments, turbine pitch control (not shown) regulates rotor speed.

[0068] Further aspects of the invention are provided by the subject matter of the following clauses:

[0069] A method of blackstarting a power generating farm, the method comprising: with the power generating farm disconnected from an electrical grid, sending, via a controller, a blackstart command to one or more first inverter-based resources on an isolated first feeder at the power generating farm, the one or more first inverter-based resources having energy storage; upon receipt of the blackstart command, implementing a blackstart mode using the one or more first inverter-based resources having the energy storage, wherein implementing the blackstart mode comprises using a first converter of the one or more first inverter-based resources with the energy storage to establish an auxiliary voltage and an auxiliary frequency to one or more auxiliary loads thereof and using a second converter of the one or more first inverter-based resources with the energy storage to establish a first voltage and a first frequency to the isolated first feeder; energizing one or more first inverter-based resources without blackstart capability via the isolated first feeder; switching from the blackstart mode to a normal mode; and connecting the power generating farm to the electrical grid to support the blackstarting or restoration of portions of the electrical grid.

[0070] The method of any preceding clause, further comprising: energizing one or more second feeders having one or more second inverter-based resources via the isolated first feeder; and sequentially starting the one or more second inverter-based resources.

[0071] The method of any preceding clause, wherein the one or more second inverter-based resources are without blackstart capability, and wherein sequentially starting the one or more second inverter-based resources further comprises sequentially starting the one or more second inverter-based resources without blackstart capability.

[0072] The method of any preceding clause, further comprising disconnecting the power generating farm from the electrical grid prior to sending the blackstart command.

[0073] The method of any preceding clause, wherein disconnecting the power generating farm from the electrical grid further comprises: opening a plurality of switchgears to a pl ural ity of feeders and a main switchgear to a transformer of the power generating farm.

[0074] The method of any preceding clause, further comprising: prior to sending the blackstart command, setting an inertial power regulator reference to zero, the first frequency to a baseline frequency reference, and the first voltage to a baseline voltage reference, where the baseline voltage reference is less than or equal to a nominal voltage and the baseline frequency reference is less than or equal to a nominal frequency.

[0075] The method of any preceding clause, wherein implementing the blackstart mode using the one or more first inverter-based resources with the energy storage further comprises: ramping up the first voltage of the one or more first inverter-based resources with the energy' storage at a predetermined rate to a first voltage reference with a first frequency reference, wherein the predetermined rate and reduced voltage/frequency reduce transient and steady-state loading during the blackstart mode.

[0076] The method of any preceding clause, further comprising increasing the first voltage reference and the first frequency reference to a second voltage reference and a second frequency reference, respectively.

[0077] The method of any preceding clause, wherein the auxiliary power supplies at least one of auxiliary' loads, cable charging, or losses of the one or more first inverter-based resources.

[0078] The method of any preceding clause, wherein switching from the blackstart mode to the normal mode further comprises sending a signal to the one or more first inverter-based resources at the power generating farm having the energy' storage to operate in the normal mode.

[0079] The method of any preceding clause, further comprising energizing the power generating farm before connecting the power generating farm to the electrical grid.

[0080] The method of any preceding clause, wherein the one or more first inverter-based resources and the one or more second inverter-based resources comprises a plurality of wind turbines, wherein at least the one or more first inverterbased resources have grid forming capability.

[0081] The method of any preceding clause, wherein implementing the blackstart mode further comprises: operating the first converter such that the auxiliary' voltage and the auxiliary frequency are independent of the first voltage and the first frequency established by the second converter.

[0082] The method of any preceding clause, wherein the one or more first inverter-based resources with the energy storage is one of a double-fed induction generator or a full-power conversion system and the first converter is at least one of a machine-side converter or a grid-side converter.

[0083] The method of any preceding clause, wherein switching from the blackstart mode to the normal mode further comprises connecting the one or more auxiliary loads to the isolated first feeder, thereby bringing one or more auxiliary' loads to be fed by the first feeder.

[0084] A wind farm, the wind farm comprising: a plurality of wind turbines capable of being connected to an electrical grid via a transmission network; 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 the electrical grid, sending a blackstart command to one or more first wind turbines on an isolated first feeder at the wind farm, the one or more first wind turbines having energy storage; upon receipt of the blackstart command, implementing a blackstart mode using the one or more first wind turbines having the energy’ storage to establish a voltage and a frequency on the isolated first feeder, wherein implementing the blackstart mode comprises using a first converter of the one or more first inverter-based resources with the energy storage to establish an auxiliary voltage and an auxiliary’ frequency to one or more auxiliary loads thereof and using a second converter of the one or more first inverter-based resources with the energy storage to establish a first voltage and a first frequency to the isolated first feeder; energizing one or more first inverter-based resources without blackstart capability' via the isolated first feeder; switching from the blackstart mode to a normal mode; and connecting the power generating farm to the electrical grid to support the blackstarting or restoration of portions of the electrical grid.

[0085] The wind farm of any preceding clause, wherein the plurality of operations further comprises: energizing one or more second feeders having one or more second wind turbines w ithout blackstart capability via the isolated first feeder; and sequentially starting the one or more second wind turbines without blackstart capability’.

[0086] The w ind farm of any preceding clause, wherein the plurality of operations further comprises: disconnecting the w ind farm from the electrical grid prior to sending the blackstart command, wherein disconnecting the w ind farm from the electrical grid further comprises opening a plurality of switchgears to a plurality of feeders and a main switchgear to a transformer of the wind farm.

[0087] The wind farm of any preceding clause, wherein the plurality of operations further comprises: prior to sending the blackstart command, setting an inertial power regulator reference to zero, the first frequency to a baseline frequency reference, and the first voltage to a baseline voltage reference, where the baseline voltage reference is less than or equal to a nominal voltage and the baseline frequency reference is less than or equal to a nominal frequency.

[0088] 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, the method comprising: with the power generating farm disconnected from an electrical grid, sending, via a controller, a blackstart command to one or more first inverter-based resources on an isolated first feeder at the power generating farm, the one or more first inverterbased resources having energy storage; upon receipt of the blackstart command, implementing a blackstart mode using the one or more first inverter-based resources having the energy storage, wherein implementing the blackstart mode comprises using a first converter of the one or more first inverter-based resources with the energy storage to establish an auxiliary voltage and an auxiliary frequency to one or more auxiliary loads thereof and using a second converter of the one or more first inverter-based resources with the energy⁷ storage to establish a first voltage and a first frequency to the isolated first feeder; energizing one or more first inverter-based resources without blackstart capability' via the isolated first feeder; switching from the blackstart mode to a normal mode; and connecting the power generating farm to the electrical grid to support the blackstarting or restoration of portions of the electrical grid.

2. The method of claim 1, further comprising: energizing one or more second feeders having one or more second inverterbased resources via the isolated first feeder; and sequentially starting the one or more second inverter-based resources.

3. The method of claim 2, wherein the one or more second inverter-based resources are without blackstart capability, and wherein sequentially starting the one or more second inverter-based resources further comprises sequentially starting the one or more second inverter-based resources without blackstart capability.

4. The method of claim 1. further comprising disconnecting the power generating farm from the electrical grid prior to sending the blackstart command.

5. The method of claim 4, wherein disconnecting the power generating farm from the electrical grid further comprises: opening a plurality of switchgears to a plurality of feeders and a main switchgear to a transformer of the power generating farm.

6. The method of claim 1. further comprising: prior to sending the blackstart command, setting an inertial power regulator reference to zero, the first frequency to a baseline frequency reference, and the first voltage to a baseline voltage reference, where the baseline voltage reference is less than or equal to a nominal voltage and the baseline frequency reference is less than or equal to a nominal frequency.

7. The method of claim 1, wherein implementing the blackstart mode using the one or more first inverter-based resources with the energy storage further comprises: ramping up the first voltage of the one or more first inverter-based resources with the energy storage at a predetermined rate to a first voltage reference with a first frequency reference, wherein the predetermined rate and reduced voltage/frequency reduce transient and steady-state loading during the blackstart mode.

8. The method of claim 7. further comprising increasing the first voltage reference and the first frequency reference to a second voltage reference and a second frequency reference, respectively.

9. The method of claim 1 , wherein the auxiliary power supplies at least one of auxiliary’ loads, cable charging, or losses of the one or more first inverter-based resources.

10. The method of claim 1, wherein sw itching from the blackstart mode to the normal mode further comprises sending a signal to the one or more first inverterbased resources at the power generating farm having the energy storage to operate in the normal mode.

11. The method of claim 1, further comprising energizing the power generating farm before connecting the power generating farm to the electrical grid.

12. The method of claim 1, wherein the one or more first inverter-based resources and the one or more second inverter-based resources comprises a plurality of wind turbines, w herein at least the one or more first inverter-based resources have grid forming capability⁷.

13. The method of claim 1, wherein implementing the blackstart mode further comprises: operating the first converter such that the auxiliary voltage and the auxiliary frequency are independent of the first voltage and the first frequency established by the second converter.

14. The method of claim 1, wherein the one or more first inverter-based resources with the energy' storage is one of a double-fed induction generator or a fullpower conversion system and the first converter is at least one of a machine-side converter or a grid-side converter.

15. The method of claim 1, wherein switching from the blackstart mode to the normal mode further comprises connecting the one or more auxiliary loads to the isolated first feeder, thereby bringing one or more auxiliary loads to be fed by the first feeder.

16. A wind farm, the wind farm comprising: a plurality' of wind turbines capable of being connected to an electrical grid via a transmission network; and a controller comprising at least one processor, the at least one processor configured to perform a plurality' of operations, the plurality⁷ of operations comprising: with the w ind farm disconnected from the electrical grid, sending a blackstart command to one or more first wind turbines on an isolated first feeder at the wind farm, the one or more first wind turbines having energy⁷ storage: upon receipt of the blackstart command, implementing a blackstart mode using the one or more first wind turbines having the energy storage to establish a voltage and a frequency on the isolated first feeder, wherein implementing the blackstart mode comprises using a first converter of the one or more first inverter-based resources with the energy storage to establish an auxiliary voltage and an auxiliary' frequency⁷ to one or more auxiliary loads thereof and using a second converter of the one or more first inverter-based resources with the energy⁷ storage to establish a first voltage and a first frequency to the isolated first feeder; energizing one or more first inverter-based resources without blackstart capability via the isolated first feeder; switching from the blackstart mode to a normal mode; and connecting the power generating farm to the electrical grid to support the blackstarting or restoration of portions of the electrical grid.

17. The wind farm of claim 16, wherein the plurality of operations further comprises: energizing one or more second feeders having one or more second wind turbines without blackstart capability via the isolated first feeder; and sequentially starting the one or more second wind turbines without blackstart capability.

18. The wind farm of claim 16, wherein the plurality of operations further comprises: disconnecting the wind farm from the electrical grid prior to sending the blackstart command, wherein disconnecting the wind farm from the electrical grid further comprises opening a plurality of switchgears to a plurality of feeders and a main switchgear to a transformer of the wind farm.

19. The wind farm of claim 16. wherein the plurality of operations further comprises: prior to sending the blackstart command, setting an inertial power regulator reference to zero, the first frequency to a baseline frequency reference, and the first voltage to a baseline voltage reference, where the baseline voltage reference is less than or equal to a nominal voltage and the baseline frequency reference is less than or equal to a nominal frequency.

20. The wind farm of claim 16, wherein implementing the blackstart mode using the one or more first inverter-based resources with the energy storage further comprises: ramping up the first voltage of the one or more first inverter-based resources with the energy’ storage at a predetermined rate to a first voltage reference with a first frequency reference, wherein the predetermined rate and reduced voltage/frequency reduce transient and steady-state loading during the blackstart mode.