System and method for boosting voltage at a voltage terminal of an inverter-based resource based on active power or frequency

Abstract

A method for boosting voltage at a voltage terminal of an inverter-based resource coupled to a utility grid to maintain stable operation during recovery of a utility grid transient event includes receiving, via a voltage regulator of a controller, a voltage reference signal. The method also includes receiving, via a power-voltage boost module of the controller, an active power output of the inverter-based resource and determining, via the power-voltage boost module of the controller, a rate of change of the active power output. Further, the method includes receiving, via a frequency-voltage boost function of the controller, a frequency signal representative of a grid frequency of the utility grid and determining, via the frequency-voltage boost function of the controller, a downward rate of change of the frequency signal. In response to the rate of change of the active power output exceeding an offset and / or the downward rate of change of the frequency signal exceeding a ramp down rate offset, the method includes generating an overall voltage boost signal for the voltage reference.

Description

701327-WO- 1 / GECW-l 325-PCTSYSTEM AND METHOD FOR BOOSTING VOLTAGE AT A VOLTAGE TERMINAL OF AN INVERTER-BASED RESOURCE BASED ON ACTIVE POWER OR FREQUENCYFIELD

[0001] The present disclosure described herein generally relates inverter-based resources (IBRs), and more specifically, to systems and methods for boosting voltage at the IBR terminal to maintain stable operation, e.g., at extreme grid conditions.BACKGROUND

[0002] Wind turbine generators utilize wind energy to produce electrical power. Wind turbine generators typically include a rotor having multiple rotor blades that transform wind energy into rotational motion of a drive shaft, which in turn is utilized to drive an electrical generator to produce electrical power. Each of the rotor blades may be pitched to increase or decrease the rotational speed of the rotor. A power output of a wind turbine generator increases with wind speed until the wind speed reaches a rated wind speed for the turbine. At and above the rated wind speed, the wind turbine generator operates at a rated power. The rated power is an output power at which a wind turbine generator can operate with a level of fatigue to turbine components that is predetermined to be acceptable. At wind speeds higher than a certain speed, or at a wind turbulence level that exceeds a predetermined magnitude, typically referred to as a '‘trip limit” or “monitor set point limit,” wind turbines may be shut down, or the loads may be reduced by regulating the pitch of the rotor blades or braking the rotor, in order to protect wind turbine components against damage.

[0003] Variable speed operation of the wind turbine generator facilitates enhanced energy capture by the wind turbine generator when compared to a constant speed operation of the wind turbine generator. However, variable speed operation of the wind turbine generator produces electricity having varying voltage and / or frequency. More specifically, the frequency of the electricity generated by the variable speed wind turbine generator is proportional to the speed of rotation of the rotor. A power converter may be coupled between the electric generator and a utility grid. The power converter outputs electricity having a fixed voltage and frequency for delivery on the utility grid.701327-WO- 1 / GECW-l 325-PCT

[0004] The terminal voltage control of inverter-based resources (IBR), such as wind turbines, plays an important operational role for the IBRS while ensuring its stable operation under various grid events or conditions. When the active power output of an IBR starts to ramp up, which can happen after a fault clearing, after a frequency event, or other scenarios, it is beneficial to temporarily boost the voltage at the IBR terminal, to facilitate the power transfer, particularly in weak grids.

[0005] For example, after a grid fault clearing, the active power of an IBR starts to ramp up to the rated value, yet the voltage can collapse if the grid is weak or in a disturbed state that is unable to absorb high power. Such a voltage collapse can cause the IBR to trip eventually. A similar voltage collapse can occur in weak grids if the IBR is programmed to ramp up power when grid frequency drops.

[0006] Accordingly, the present disclosure is directed to systems and methods for boosting voltage at the IBR terminal to maintain stable operation even at extreme grid conditions to address the aforementioned issues.BRIEF DESCRIPTION

[0007] Aspects and advantages of the invention w ill 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.

[0008] In an aspect, the present disclosure is directed to a method for boosting voltage at a voltage terminal of an inverter-based resource coupled to a uti 1 ity grid to maintain stable operation during recovery of a utility grid transient event. The method includes receiving, via a voltage regulator of a controller, a voltage reference signal. The method also includes receiving, via a power-voltage boost module of the controller, an active power output of the inverter-based resource and determining, via the power-voltage boost module of the controller, a rate of change of the active power output. Further, the method includes receiving, via a frequency-voltage boost function of the controller, a frequency signal representative of a grid frequency of the utility’ grid and determining, via the frequency -voltage boost function of the controller, a downward rate of change of the frequency signal. In response to the rate of change of the active power output exceeding an offset and / or the dow nw ard rate of change of the frequency signal exceeding a ramp down rate offset, the method701327-WO- 1 / GECW-l 325-PCT includes generating an overall voltage boost signal for the voltage reference.

[0009] In another aspect, the present disclosure is directed to a system for boosting voltage at a voltage terminal of an inverter-based resource to maintain stable operation during recovery of a utility grid transient event. The inverter-based resource is coupled to a utility grid. The system includes a controller having a voltage regulator for receiving a voltage reference signal, a power-power-voltage boost module, and a frequency-voltage boost function. The power-power-voltage boost module is configured for receiving an active power output of the inverter-based resource and determining a rate of change of the active power output. The frequencyvoltage boost function is configured for receiving a frequency signal representative of a grid frequency of the utility grid, determining a downward rate of change of the frequency signal, and in response to the rate of change of the active power output exceeding an offset and the downward rate of change of the frequency signal exceeding a ramp down rate offset, and generating an overall voltage boost signal for the voltage reference.

[0010] 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

[0011] 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:

[0012] FIG. 1 illustrates a block diagram of a pow er generation system according to the present disclosure;

[0013] FIG. 2 illustrates a perspective view of a portion of a wind turbine that may be used in the power generation system shown in FIG. 1;

[0014] FIG. 3 illustrates a partially cut-aw ay view' of a portion of the wind turbine shown in FIG. 2;

[0015] FIG. 4 illustrates a block diagram of the wind turbine shown in FIG. 2;701327-WO- 1 / GECW-l 325-PCT

[0016] FIG. 5 illustrates a block diagram of an inverter-based resource that may include the wind turbine shown in FIG. 2;

[0017] FIG. 6 illustrates a flow diagram of an embodiment of a method for boosting voltage at a voltage terminal of an inverter-based resource to maintain stable operation during recovery of a utility grid transient event according to the present disclosure;

[0018] FIG. 7 illustrates a block diagram of an embodiment of a control system of an inverter-based resource having a power-voltage boost module and a frequencyvoltage boost function according to the present disclosure; and

[0019] FIG. 8 illustrates a block diagram of an embodiment of control logic of the power-voltage boost module and the frequency -voltage boost function of FIG. 7.DETAILED DESCRIPTION

[0020] 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 an 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.

[0021] Generally, the present disclosure is directed to systems and methods for boosting voltage at a voltage terminal of an inverter-based resource to maintain stable operation during recovery of a utility grid transient event. As used herein, inverterbased resources generally refer to electrical devices that can generate or absorb electric power through switching of power-electronic devices. Accordingly, inverterbased resource may include wind turbine power systems, solar inverters, energystorage systems, STATCOMs. or hydro-power systems. For example, in an embodiment, an inverter-based resource may be a wind turbine power system having a rotor-side converter, a line-side converter, and a doubly fed induction generator (DFIG) connected to the electrical grid as further described herein.701327-WO- 1 / GECW-l 325-PCT

[0022] More specifically, inverter-based resources of the present disclosure generally include a controller having a voltage regulator for receiving a voltage reference signal, a power-voltage boost module, and a frequency -voltage boost function. In an embodiment, the power-power-voltage boost module is configured for receiving an active power output of the inverter-based resource and determining a rate of change of the active power output. Further, in an embodiment, the frequencyvoltage boost function is configured for receiving a frequency signal representative of a grid frequency of the utility grid, determining a downward rate of change of the frequency signal, and in response to the rate of change of the active powder output exceeding an offset and the downw ard rate of change of the frequency signal exceeding a ramp down rate offset, generating an overall voltage boost signal for the voltage reference.

[0023] Thus, the frequency-voltage boost function is designed to boost the voltage reference based on a dropping grid frequency. This can be important for grid forming inverter-based resources that act to increase active power when grid frequency is decreasing. Further, in an embodiment, the boost in voltage is a consequence of a power increase that is frequency driven. In addition, the power-voltage boost module includes features that can activate the voltage boost more selectively based on one or more pow er operating points and features to avoid overvoltage. These features can be equally relevant for both grid-following and grid-forming inverter-based resources.

[0024] Referring now to the drawings, FIG. 1 illustrates a block diagram of a power generation system 1 that includes a power generator 2. The power generator 2 includes one or more power generation units 3. The power generation units 3 may include, for example, wind turbines, solar cells, fuel cells, geothermal generators, hydropower generators, and / or other devices that generate power from renewable and / or non-renewable energy sources. Although three power generation units 3 are shown in the illustrated embodiment, in other embodiments, the power generator 2 may include any suitable number of pow er generation units 3, including only one power generation unit 3.

[0025] Further, in an embodiment, the power generator 2 is coupled to a power converter 4, or a power converter system, that converts a substantially direct current (DC) pow er output from the pow er generator 2 to alternating current (AC) power.701327-WO- 1 / GECW-l 325-PCTThe AC power is transmited to an electrical distribution network 5, or “grid.” In an embodiment, the power converter 4 adjusts an amplitude of the voltage and / or current of the converted AC power to an amplitude suitable for electrical distnbution network 5 and provides AC power at a frequency and a phase that are substantially equal to the frequency and phase of the electrical distribution network 5. Moreover, in an embodiment, the power converter 4 provides three phase AC power to the electrical distribution network 5. Alternatively, the power converter 4 provides single phase AC power or any other number of phases of AC power to the electrical distribution network 18. Furthermore, in some embodiments, the power generation system 1 may include more than one power converter. For example, in an embodiment, each power generation unit may be coupled to a separate power converter.

[0026] In an embodiment, the power generation units 3 may include solar panels coupled to form one or more solar array to facilitate operating the power generation system 1 at a desired power output. Each power generation unit 3 may be an individual solar panel or an array of solar panels. In an embodiment, the power generation system 1 includes a plurality of solar panels and / or solar arrays coupled together in a series-parallel configuration to facilitate generating a desired current and / or voltage output from the power generation system 1. In an embodiment, the solar panels include one or more of a photovoltaic panel, a solar thermal collector, or any other device that converts solar energy to electrical energy. In an embodiment, each solar panel is a photovoltaic panel that generates a substantially direct current power as a result of solar energy striking solar panels. Further, in an embodiment, the solar array is coupled to the power converter 4, or power converter system, that converts the DC power to alternating current power that is transmitted to the electrical distribution network 5.

[0027] Furthermore, in an embodiment, the power generation units 3 include one or more wind turbines coupled to facilitate operating the power generation system 1 at a desired pow er output. Each wind turbine generates substantially direct current power. The wind turbines are coupled to the power converter 4 that converts the DC power to AC power that is transmited to the electrical distribution network 5. Methods and systems will be further described herein with reference to such a wind turbine based power generation system. However, the methods and systems described701327-WO- 1 / GECW-l 325-PCT herein are applicable to any type of electric generation system including, for example, fuel cells, geothermal generators, hydropower generators, and / or other devices that generate power from renewable and / or non-renewable energy sources.

[0028] Referring now to FIG. 2, a perspective view of a wind turbine 10 that may be used in the power generation system 1 of FIG. 1 is illustrated according to the present disclosure. FIG. 3 illustrates a partially cut-away perspective view of a portion of the wind turbine 10 according to the present disclosure. The wind turbine 10 described and shown herein is a wind turbine generator for generating electrical power from wind energy. Moreover, the wind turbine 10 described and illustrated herein includes a horizontal-axis configuration, however, in some embodiments, the wind turbine 10 may include, in addition or alternative to the horizontal-axis configuration, a vertical-axis configuration (not shown). Further, the wind turbine 10 may be coupled to an electrical load (not shown in FIG. 2), such as, but not limited to, a power grid, for receiving electrical pow er therefrom to drive operation of the wind turbine 10 and / or its associated components and / or for supplying electrical power generated by the wind turbine 10 thereto. Although only one wind turbine 10 is shown in FIGS. 2 and 3, in some embodiments, a plurality of wind turbines 10 may be grouped together, sometimes referred to as a “wind farm.”

[0029] Furthermore, as shown, the wind turbine 10 includes a nacelle 12 and a rotor 14 coupled to the nacelle 12 for rotation with respect to the nacelle 12 about an axis of rotation 20. In an embodiment, the nacelle 12 is mounted on a tower 16, however, in some embodiments, in addition or alternative to the tower-mounted nacelle 12, the nacelle 12 may be positioned adjacent the ground and / or a surface of water. The height of the tower 16 may be any suitable height enabling the wind turbine 10 to function as described herein. The rotor 14 includes a hub 22 and a plurality of rotor blades 24 (sometimes referred to as “airfoils”) extending radially outwardly from the hub 22 for converting wind energy into rotational energy. Although the rotor 14 is described and illustrated herein as having three rotor blades 24, the rotor 14 may have any number of rotor blades 24. Further, the rotor blades 24 may each have any length that allows the wind turbine 10 to function as described herein.

[0030] Referring now' to FIG. 3, the wind turbine 10 includes an electrical701327-WO- 1 / GECW-l 325-PCT generator 26 coupled to the rotor 14 for generating electrical power from the rotational energy generated by the rotor 14. The generator 26 may be any suitable type of electrical generator, such as. but not limited to, a wound rotor induction generator, a double-fed induction generator (DFIG, also known as dual-fed asynchronous generators), a permanent magnet (PM) synchronous generator, an electrically excited synchronous generator, and a switched reluctance generator. The generator 26 includes a stator (not shown) and a rotor (not shown) with an air gap included therebetween. The rotor 14 includes a rotor shaft 28 coupled to the rotor hub 22 for rotation therewith. The generator 26 is coupled to the rotor shaft 28 such that rotation of the rotor shaft 28 drives rotation of the generator rotor, and therefore operation of the generator 26. In an embodiment, the generator rotor has a generator shaft 30 coupled thereto and coupled to the rotor shaft 28 such that rotation of rotor shaft 28 drives rotation of the generator rotor. In other embodiments, the generator rotor is directly coupled to the rotor shaft 28, sometimes referred to as a “direct-drive wind turbine.” In an embodiment, the generator shaft 30 is coupled to the rotor shaft 28 through a gearbox 32. although in other embodiments the generator shaft 30 is coupled directly to the rotor shaft 28.

[0031] The torque of the rotor 14 drives the generator rotor to generate variable frequency AC electrical power from rotation of the rotor 14. The generator 26 has an air gap torque between the generator rotor and stator that opposes the torque of the rotor 14. A power conversion assembly 34 is coupled to the generator 26 for converting the variable frequency AC to a fixed frequency AC for delivery to an electrical load (not shown in FIG. 3), such as, but not limited to a pow er grid (not shown in FIG. 3), coupled to the generator 26. The power conversion assembly 34 may include a single frequency converter or a plurality of frequency converters configured to convert electricity generated by the generator 26 to electricity suitable for delivery over the pow er grid. The pow er conversion assembly 34 may also be referred to herein as a power converter. The power conversion assembly 34 may be located anywhere within or remote to the wind turbine 10. For example, the power conversion assembly 34 may be located within a base (not shown) of the tower 16.

[0032] In some embodiments, the wind turbine 10 includes a rotor speed limiter, for example, but not limited to a disk brake 36. The disk brake 36 brakes rotation of701327-WO- 1 / GECW-l 325-PCT the rotor 14 to, for example, slow rotation of the rotor 14, the brake rotor 14 against full wind torque, and / or reduce the generation of electrical power from the generator 26. Furthermore, in some embodiments, the wind turbine 10 includes a yaw system 38 for rotating the nacelle 12 about an axis of rotation 40 for changing a yaw of the rotor 14, and more specifically for changing a direction faced by the rotor 14 to, for example, adjust an angle between the direction faced by the rotor 14 and a direction of wind.

[0033] In an embodiment, the wind turbine 10 includes a variable blade pitch system 42 for controlling, including but not limited to changing, a pitch angle of the rotor blades 24 (shown in FIGS. 2-3) with respect to a wind direction. The pitch system 42 is coupled to the hub 22 and the rotor blades 24 for changing the pitch angle of the rotor blades 24 by rotating the rotor blades 24 with respect to the hub 22. The pitch actuators may include any suitable structure, configuration, arrangement, means, and / or components, whether described and / or shown herein, such as, but not limited to, electrical motors, hydraulic cylinders, springs, and / or servomechanisms. Moreover, the pitch actuators may be driven by any suitable means, whether described and / or shown herein, such as, but not limited to, hydraulic fluid, electrical power, electro-chemical power, and / or mechanical pow er, such as, but not limited to, spring force.

[0034] Referring now to FIG. 4, a block diagram of an embodiment of a wind turbine 10 according to the present disclosure is illustrated. In an embodiment, as shown, the wind turbine 10 includes one or more system controllers 44 coupled to at least one component of the wind turbine 10 for generally controlling operation of the wind turbine 10 and / or controlling operation of the components thereof, regardless of whether such components are described and / or shown herein. For example, in an embodiment, the system controller 44 is coupled to the pitch system 42 for generally controlling the rotor 14. In an embodiment, the system controller 44 is mounted within the nacelle 12 (shown in FIG. 3), however, additionally or alternatively, one or more system controllers 44 may be remote from the nacelle 12 and / or other components of the wind turbine 10. The system controllers 44 may be used for overall system monitoring and control including, without limitation, pitch and speed regulation, high-speed shaft and yaw' brake application, yaw and pump motor701327-WO- 1 / GECW-l 325-PCT application, and / or fault monitoring. Alternative distributed or centralized control architectures may be used in some embodiments.

[0035] In an embodiment, the wind turbine 10 includes a lurality of sensors, for example, the sensors 50, 54, and 56. The sensors 50, 54, and 56 measure a variety of parameters including, without limitation, operating conditions and atmospheric conditions. Each sensor 50, 54, and 56 may be an individual sensor or may include a plurality of sensors. The sensors 50. 54. and 56 may be any suitable sensor having any suitable location within or remote to the wind turbine 10 that allows the wind turbine 10 to function as described herein. In some embodiments, the sensors 50, 54, and 56 are coupled to the system controller 44 for transmitting measurements to the system controller 44 for processing thereof.

[0036] In an embodiment, the system controller 44 includes a bus 62 or other communications device to communicate information. One or more processor(s) 64 are coupled to the bus 62 to process information, including information from the sensors 50, 54, and 56 and / or other sensor(s). The processor(s) 64 may include at least one computer. As used herein, the term computer is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a processor, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein.

[0037] The system controller 44 may also include one or more random access memories (RAM) 66 and / or other storage device(s) 68. RAM(s) 66 and storage device(s) 68 are coupled to the bus 62 to store and transfer information and instructions to be executed by the processor(s) 64. RAM(s) 66 (and / or the storage device(s) 68. if included) can also be used to store temporary variables or other intermediate information during execution of instructions by the processor(s) 64. The system controller 44 may also include one or more read only memories (ROM) 70 and / or other static storage devices coupled to the bus 62 to store and provide static (i.e., non-changing) information and instructions to the processor(s) 64. The processor(s) 64 process information transmitted from a plurality of electrical and electronic devices that may include, without limitation, speed and power transducers. Instructions that are executed include, without limitation, resident conversion and / or701327-WO- 1 / GECW-l 325-PCT comparator algorithms. The execution of sequences of instructions is not limited to any specific combination of hardware circuitry’ and software instructions.

[0038] The system controller 44 may also include, or may be coupled to. input / output device(s) 72. Input / output device(s) 72 may include any device known in the art to provide input data to system controller 44 and / or to provide outputs, such as, but not limited to, yaw control and / or pitch control outputs. Instructions may be provided to RAM 66 from the storage device 68 including, for example, a magnetic disk, a ROM integrated circuit, CD-ROM, and / or DVD, via a remote connection that is either wired or wireless providing access to one or more electronically accessible media. In some embodiments, hard-wired circuitry can be used in place of or in combination with software instructions. Thus, execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions, whether described and / or show n herein.

[0039] Also, in an embodiment, the input / output device(s) 72 may include, without limitation, computer peripherals associated with an operator interface such as a mouse and a keyboard (neither shown in FIG. 4). Alternatively, other computer peripherals may also be used that may include, for example, a scanner (not shown in FIG. 4). Furthermore, in an embodiment, additional output channels may include, for example, an operator interface monitor (not shown in FIG. 4). The system controller 44 may also include a sensor interface 74 that allows the system controller 44 to communicate with the sensors 50, 54, and 56 and / or other sensor(s). The sensor interface 74 may include one or more analog-to-digital converters that convert analog signals into digital signals that can be used by the processors) 64.

[0040] Referring now to FIG. 5, a block diagram of a system having an inverterbased resource 150 is illustrated according to the present disclosure. The inverterbased resource 150 may be used with, or included within, the wind turbine 10 (shown in FIGS. 2 and 3). The inverter-based resource 150 includes an energy source, for example, the generator 26. Although described herein as the wind turbine generator 26, the energy source may include any type of electrical generator that allows inverter-based resource 150 to function as described herein, e g. a solar power generation system. The inverter-based resource 150 also includes a powder converter, such as, the power conversion assembly 34. The power conversion assembly 34701327-WO- 1 / GECW-l 325-PCT receives electrical power (e.g., Pv) 132 generated by generator 26 and converts the electrical power 132 to an electrical power (e.g.. Pt) 134 (referred to herein as terminal power 134) suitable for transmission over an electric power transmission and distribution grid 136 (referred to herein as utility grid 136). A terminal voltage (e.g., Vt) 138 is defined at a node between power conversion assembly 34 and utility' grid 136. A bulk power system 140 is coupled to utility grid 136. Bulk power system 140 includes a plurality of loads and / or power sources.

[0041] In an embodiment, the inverter-based resource 150 includes a griddependent power limiter system 152. For example, in an embodiment, the controller 44 (shown in FIG. 4), is programmed to perform the functions of the grid-dependent power limiter system 152. However, in alternative embodiments, the functions of grid-dependent power limiter system 152 may be performed by any circuitry configured to allow the inverter-based resource 150 to function as described herein. The power limiter system 152 is configured to identity' the occurrence of a grid transient event and provide the power conversion assembly 34 with signals that facilitate reducing pole-slipping and providing a stable recovery from the gnd event. In certain embodiments, the power conversion assembly 34 responds according to the signals provided by the power limiter system 152 and substantially eliminates poleslipping.

[0042] Generally, upon detection of a grid transient event (e.g. a grid fault), the power limiter system 152 provides signals to reduce the power output of the power conversion assembly 34. During recovery from the grid transient event, the power limiter system 152 provides signals to increase the active power output of the power conversion assembly 34. In some embodiments, the power limiter system 152 provides a signal, or signals, to increase the active power output of the power conversion assembly 34 gradually until the output power of the power conversion assembly 34 is returned to its pre-fault level.

[0043] Furthermore, as shown, the inverter-based resource 150 includes a powervoltage boost module 241 configured to generate an overall voltage boost signal 243 during recovery from a grid transient event, which is further described herein below. In an embodiment, a controller, for example, but not limited to, controller 44 (show n in FIG. 4), is programmed to perform the functions of the pow er-voltage boost701327-WO- 1 / GECW-l 325-PCT module 241. However, in alternative embodiments, the functions of the powervoltage boost module 241 may be performed by any circuitry configured to allow the inverter-based resource 150 to function as described herein. In certain embodiments, the power conversion assembly 34 responds according to the signals provided by the pow er-voltage boost module 241.

[0044] A grid event, also referred to herein as a grid transient event, may leave the utility’ grid 136 in a degraded mode where the grid impedance is too high to accommodate power generated by the generator 26. An example of a grid event includes a short-circuit fault on one of the transmission lines within the utility grid 136. Electrical transmission protection actions remove the faulted portion of the utility grid 136 to permit operation of the remaining un-faulted portion of the utility grid 136. A transmission path remains that is degraded in its ability’ to transmit power from the inverter-based resource 150 to bulk the power system 140. Such grid events cause a brief period of low voltage on the utility grid 136 prior to clearing the faulted portion of the utility grid 136. Typically, the terminal voltage 138 will be significantly degraded at the time of the grid event.

[0045] Still referring to FIG. 5, as shown, the pow er conversion assembly 34 is configured to receive control signals 154 from a converter interface controller 156. The control signals 154 are based on sensed operating conditions or operating characteristics of the wind turbine 10 as described herein and used to control the operation of the power conversion assembly 34. Examples of measured operating conditions may include, but are not limited to, a terminal grid voltage, a PLL error, a stator bus voltage, a rotor bus voltage, and / or a current. For example, the sensor 54 measures the terminal voltage 138 and transmits a terminal voltage feedback signal 160 to a voltage regulator 184. A sensor, such as sensor 54, measures the electrical power 134 and transmits an electrical pow er feedback signal 161 to the power-voltage boost module 241. The power-voltage boost module 241 generates the voltage boost signal 243 based at least partially on the electrical power feedback signal 161 and transmits the voltage boost signal 243 to the voltage regulator 184. The voltage regulator 184 generates a reactive current command signal 168 based at least partially on the voltage boost signal 243 and transmits the reactive current command signal 168 to the converter interface controller 156. In other grid forming embodiments, the701327-WO- 1 / GECW-l 325-PCT voltage regulator 184 may generate a voltage command instead of a reactive current command based at least partially on the voltage boost signal 243.

[0046] In some embodiments, the power limiter system 152 also receives the terminal voltage feedback signal 160. Based at least partially on the terminal voltage feedback signal 160, the power limiter system 152 determines when a grid transient event occurs and / or concludes and generates a real current limiter signal 166 to limit active power output of the power conversion assembly 34 during a grid transient event and gradually increase active power output of the power conversion assembly 34 on conclusion of the grid transient event. The power limiter system 152 transmits the real current limiter signal 166 to the converter interface controller 156. In an alternative embodiment, the converter interface controller 156 is included within the system controller 44. Other operating condition feedback signals from other sensors also may be used by the controller 44 and / or the converter interface controller 156 to control the power conversion assembly 34.

[0047] Referring now to FIG. 6, a flow diagram of an embodiment of a method 200 for boosting voltage at a voltage terminal of an inverter-based resource, such as the inverter-based resource 150, to maintain stable operation during recovery of a utility grid transient event is illustrated. Further, the method 200 is described herein with reference to the wind turbine 10 and the inverter-based resource 150 of FIGS. 2- 5. However, it should be appreciated that the disclosed method 200 may be implemented with any inverter-based resources in addition to wind turbines having any other suitable configurations. In addition, although FIG. 6 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.

[0048] As shown at (202), the method 200 includes receiving, via a voltage regulator of the controller, a voltage reference signal. As shown at (204). the method 200 includes receiving, via a voltage boost module of the controller, an active power output of the inverter-based resource. As show n at (206), the method 200 includes determining, via the voltage boost module of the controller, a rate of change of the701327-WO- 1 / GECW-l 325-PCT active power output. As shown at (208), the method 200 includes receiving, via a frequency -voltage boost function of the controller, a frequency signal representative of a grid frequency of the utility grid. As shown at (210). the method 200 includes determining, via the frequency-voltage boost function of the controller, a downw ard rate of change of the frequency signal. As shown at (212), the method 200 includes, in response to the rate of change of the active power output exceeding an offset and / or the downward rate of change of the frequency signal exceeding a ramp down rate offset, generating an overall voltage boost signal for the voltage reference.

[0049] The method 200 of FIG. 6 can be better understood with reference to FIG.7. In particular, as shown. FIG. 7 illustrates a block diagram of a control system of the inverter-based resource 150 including the power-voltage boost module 241 described herein and a frequency -voltage boost function 244 according to the present disclosure. In an embodiment, as shown and as mentioned, the power-voltage boost module 241 and the frequency-voltage boost function 244 are together configured to output the overall voltage boost signal 243.

[0050] Further, in an embodiment, as shown in FIG. 7, the voltage regulator 184 receives the overall voltage boost signal 243 from the power-voltage boost module 241 and the frequency- voltage boost module 244, the terminal voltage feedback signal 160 (VT_FBK), and a voltage command signal (VREF) 240 from higher level voltage and / or volt-ampere reactive (Volt / VAR) regulators 247. Upon detection of certain types of grid transient events (e.g. a short-circuit fault), the pow er limiter system 152 transmits a real current limiter signal 166 (IX_CMD) to the converter interface controller 156 to reduce the output pow er of the pow er conversion assembly 34.After the grid transient event is completed, the power limiter system 152 generates signals, for example real current command signal 166, that command a gradual increase in the active power output of the pow er conversion assembly 34. During the grid transient event, e.g., the terminal voltage 138 indicates occurrence of a grid transient event, the voltage regulator 184 generates a reactive current command signal 168 (IY CMD) that increases the reactive current output by the power conversion assembly 34 to support terminal grid voltage 138 until the grid transient event is resolved.

[0051] At the resolution of the grid transient event, the reactive current command701327-WO- 1 / GECW-l 325-PCT signal 168 returns to a lower level, causing reactive current output by the power conversion assembly 34 to decrease to about its level prior to the grid transient event. As the active power output of the power conversion assembly 34 increases during recovery from the grid transient event, the power-voltage boost module 241 generates the overall voltage boost signal to improve voltage stability in weak systems during ramp of power. For other types of grid transient events (e.g. an external generator in the grid tripping offline), an increase in power output of the power conversion assembly 34 may primarily be driven by a decrease in the grid frequency. In this case, the power conversion assembly 34 may increase power output to support the overall system load, thus causing the frequency voltage boost function 244 to generate a voltage boost signal to improve voltage stability in weak systems to accommodate the increase in power flow.

[0052] Referring now to FIG. 8, a block diagram of control logic 250 of the power-voltage boost module 241 and the frequency-voltage boost function 244 according to the present disclosure is illustrated. As described above with respect to FIG. 7. in the event of a grid contingency such as a fault in a weak grid, the real current limiter signal 166 instructs the converter interface controller 156 to decrease a real component of current that the conversion assembly 34 tries to inject onto utility grid 136. Furthermore, to support the terminal voltage 138, upon a drop in terminal voltage 138 identified by voltage regulator 184 based on terminal voltage feedback signal 160, the voltage regulator 184 generates reactive current command signal 168 and sends the reactive current command signal 168 to the converter interface controller 156. The reactive current command signal 168 instructs the converter interface controller 156 to increase a reactive component of current injected onto the utility’ grid 136 upon occurrence of a grid transient event. Further, in an embodiment, the reactive current command signal 168 instructs the converter interface controller 156 to increase a reactive component of current injected onto the utility grid 136 proportional to an output of the power conversion assembly 34 during recovery of the grid transient event.

[0053] More specifically, as shown, FIG. 8 illustrates a detailed manifestation of the control logic shown in FIG. 7. In particular, the control logic 250 includes an active power path 251 and a frequency path 253. Further, as shown, the active pow er701327-WO- 1 / GECW-l 325-PCT output 161 (e.g., Pt) is used to calculate a derivative 252 of the active power output that reflects the rate of change of the active power output (e.g., PmaxRate). This active power output signal may reflect a power feedback signal or a power reference / command. If the rate of change 252 of the active power output exceeds an offset 254 (e.g., PVBstOff), the rate of change 252 can be used to generate a first voltage boost signal 256 of the active power path 251 after multiplying by a gain 258 (e.g., PVBstGn). Furthermore, as shown, a scaling factor 260 (e.g.. PVBstGnScale) can be multiplied to the first voltage boost signal 256 such that boost action is enabled when the active power output 161 exceeds a threshold (e.g., PVBstPth). Moreover, as shown, the first voltage boost signal 256 can be limited by a limiter 262 using a minimum value and a maximum value. In addition, the first voltage boost signal 256 can be filtered by a filter 264 with tunable bandwidth for up and down directions.

[0054] Still referring to FIG. 8, the frequency -voltage boost function 244 of the frequency path 253 is configured to receive a frequence signal 266. For example, in an embodiment, the frequency signal 266 described herein may correspond to an angular frequency signal from a phase-locked loop (PLL) (e.g., COPLL) and generally represents grid frequency. Thus, as shown, the frequency-voltage boost function 244 is configured to filter the frequency signal 266 via at least one filter 268 to remove high-frequency content related to noise as well as fast electrical transients not related to grid frequency changes (e.g., grid faults, phase jumps). Further, as shown at 272, the filtered frequency signal 270 (e.g., cofil) can be used to calculate a derivative that reflects the downw ard rate of change of the frequency signal. As shown at 274, the sign of the filtered frequency signal 270 can be changed so that decreases in grid frequencies manifest as a positive boost in voltage. Moreover, as shown at 276, if the downward rate of change of the frequency signal exceeds a ramp down rate offset 278 (e.g., cooff), the downward rate of change of the frequency signal can be used to generate a second voltage boost signal 280 from the frequency path 253, e.g., after multiplying by a gain 282 (e.g., FVBstGn) and applying a downward rate limit 284 (e.g., to more slowly bring down the boosted voltage after an event). In addition, as shown, the second voltage boost signal 280 may also be limited by a limiter 286 using a minimum value and a maximum value.

[0055] Accordingly, as shown, in response to the rate of change of the active701327-WO- 1 / GECW-l 325-PCT power output exceeding the offset and the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal 243 for the voltage reference may include summing the first voltage boost signal 256 from the active power path 251 and the second voltage boost signal 258 from the frequency path 253 together to determine the overall voltage boost signal 243.

[0056] In addition, as shown, the overall voltage boost signal 243 can be limited by a limiter 294 using at least a dynamic maximum limit 288 (e.g., PVBstDVLim). More specifically, in an embodiment, the dynamic maximum limit 288 may be determined as a function of a maximum allowed terminal voltage (PVBstMax) and a filtered terminal voltage (VFbkF). As an example, as shown at 290, the dynamic maximum limit 288 may be calculated by determining a difference between PVBstMax and VFbkF. Further, as shown at 292, the difference may also be filtered with dy namic bandwidth for up and down directions to determine the dynamic maximum limit 288. Thus, in such embodiments, the dynamic maximum limit 288 ensures the overall voltage boost signal 243 does not create overvoltage problem.

[0057] Exemplary embodiments of a wind turbine, power limiter system, and methods for operating a wind turbine in response to an occurrence of a grid transient event are described above in detail. The methods, wind turbine, and power-voltage boost module / frequency-voltage boost function described herein are not limited to the specific embodiments described herein, but rather, components of the wind turbine, components of the power-voltage boost module / frequency-voltage boost function, and / or steps of the methods may be utilized independently and separately from other components and / or steps described herein. For example, the power-voltage boost module / frequency-voltage boost function and methods may also be used in combination with other wind turbine power systems and methods and are not limited to practice with only the power system as described herein. Rather, the exemplary7embodiment can be implemented and utilized in connection with many other wind turbine or power system applications.

[0058] Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be701327-WO- 1 / GECW-l 325-PCT referenced and / or claimed in combination with any feature of any other drawing.

[0059] Further aspects of the invention are provided by the subject matter of the following clauses:

[0060] A method for boosting voltage at a voltage terminal of an inverter-based resource to maintain stable operation during recovery of a utility7grid transient event, the inverter-based resource coupled to a utility grid, the method comprising: receiving, via a voltage regulator of a controller, a voltage reference signal; receiving, via a power-voltage boost module of the controller, an active power output of the inverter-based resource; determining, via the power-voltage boost module of the controller, a rate of change of the active power output; receiving, via a frequencyvoltage boost function of the controller, a frequency signal representative of a grid frequency of the utility grid; determining, via the frequency -voltage boost function of the controller, a downward rate of change of the frequency signal; and in response to at least one of the rate of change of the active power output exceeding an offset or the downward rate of change of the frequency signal exceeding a ramp down rate offset, generating an overall voltage boost signal for the voltage reference.

[0061] The method of any preceding clause, wherein determining, via the powervoltage boost module of the controller, the rate of change of the active power output further comprises: calculating a derivative of the active power output that reflects the rate of change of the active power output.

[0062] The method of any preceding clause, wherein, in response to at least one of the rate of change of the active power output exceeding the offset or the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: generating a first voltage boost signal from an active power path by applying a gam and a scaling factor to the rate of change of the active power output, wherein applying the scaling factor enables boosting the voltage when the active power output exceeds a threshold.

[0063] The method of any preceding clause, further comprising limiting the first voltage boost signal by a minimum value and a maximum value and filtering the first voltage boost signal via at least one filter having a tunable bandwidth for up and down directions.701327-WO- 1 / GECW-l 325-PCT

[0064] The method of any preceding clause, wherein the frequency signal is an angular frequency signal from a phase-locked loop of the controller.

[0065] The method of any preceding clause, further comprising filtering the frequency signal to remove high-frequency content related to noise as well as fast electrical transients not related to grid frequency changes.

[0066] The method of any preceding clause, wherein determining, via the frequency -voltage boost function of the controller, the downward rate of change of the frequency signal further comprises: calculating, via the frequency-voltage boost function of the controller, a derivative of the filtered frequency signal that reflects the downward rate of change of the frequency signal.

[0067] The method of any preceding clause, further comprising changing a sign of the derivative such that decreases in grid frequencies manifest as a positive boost in voltage.

[0068] The method of any preceding clause, further comprising determining, via the frequency -voltage boost function of the controller, whether the downward rate of change of the frequency signal exceeds the ramp down rate offset and if so. multiplying the downward rate of change of the frequency signal by a gain and applying a downward rate limit to the downward rate of change of the frequency signal to determine a second voltage boost signal from a frequency path.

[0069] The method of any preceding clause, further comprising limiting the second voltage boost signal by a minimum value and a maximum value.

[0070] The method of any preceding clause, wherein, in response to at least one of the rate of change of the active power output exceeding the offset or the dow nward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: summing the first voltage boost signal from the active power path and the second voltage boost signal from the frequency path together to determine the overall voltage boost signal.

[0071] The method of any preceding clause, further comprising limiting the overall voltage boost signal by at least a dynamic maximum limit to minimize overvoltage conditions.

[0072] The method of any preceding clause, wherein the inverter-based resource701327-WO- 1 / GECW-l 325-PCT comprises a w ind turbine.

[0073] The method of any preceding clause, wherein the inverter-based resource is one of a grid-following inverter-based resource or a grid-forming inverter-based resource.

[0074] A system for boosting voltage at a voltage terminal of an inverter-based resource to maintain stable operation during recovery of a utility' grid transient event, the inverter-based resource coupled to a utility grid, the system comprising: a controller comprising: a voltage regulator for receiving a voltage reference signal; a power-power-voltage boost module, the power-power- voltage boost module configured for receiving an active pow er output of the inverter-based resource and determining a rate of change of the active power output; and a frequency-voltage boost function, the frequency -voltage boost function configured for receiving a frequency signal representative of a grid frequency of the utility7grid, determining a downward rate of change of the frequency signal, and in response to the rate of change of the active power output exceeding an offset and the downward rate of change of the frequency signal exceeding a ramp down rate offset, and generating an overall voltage boost signal for the voltage reference.

[0075] The system of any preceding clause, wherein determining the rate of change of the active power output further comprises: calculating a derivative of the active power output that reflects the rate of change of the active power output, and wherein, in response to the rate of change of the active power output exceeding the offset and the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: generating a first voltage boost signal from an active power path by applying a gain and a scaling factor to the rate of change of the active power output, wherein applying the scaling factor enables boosting the voltage when the active pow er output exceeds a threshold.

[0076] The system of any preceding clause, wherein the power-pow er-voltage boost module is further configured to limit the first voltage boost signal by a minimum value and a maximum value and filter the first voltage boost signal via at least one filter having a tunable bandwidth for up and down directions.

[0077] The system of any preceding clause, wherein the frequency -voltage boost701327-WO- 1 / GECW-l 325-PCT function is further configured to filter the frequency signal to remove high-frequencycontent related to noise as well as fast electrical transients not related to grid frequency changes, and wherein determining the downward rate of change of the frequency signal further comprises: calculating a derivative of the filtered frequency signal that reflects the downward rate of change of the frequency signal and changing a sign of the derivative such that decreases in grid frequencies manifest as a positive boost in voltage via the frequency-voltage boost function of the controller.

[0078] The system of any preceding clause, wherein the frequency -voltage boost function is further configured to multiply the downw ard rate of change of the frequency signal by a gain, apply a downw ard rate limit to the downw ard rate of change of the frequency signal to determine a second voltage boost signal from a frequency path, and limit the second voltage boost signal by a minimum value and a maximum value.

[0079] The system of any preceding clause, wherein, in response to the rate of change of the active power output exceeding the offset and the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: summing the first voltage boost signal from the active powder path and the second voltage boost signal from the frequency path together to determine the overall voltage boost signal; and limiting the overall voltage boost signal by at least a dynamic maximum limit to minimize overvoltage conditions.

[0080] This written description uses examples to disclose the invention, including the best mode, and 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

701327-WO- 1 / GECW-l 325-PCTWHAT IS CLAIMED IS:

1. A method for boosting voltage at a voltage terminal of an inverterbased resource to maintain stable operation during recovery of a utility grid transient event, the inverter-based resource coupled to a utility grid, the method comprising: receiving, via a voltage regulator of a controller, a voltage reference signal; receiving, via a power-voltage boost module of the controller, an active power output of the inverter-based resource; determining, via the power-voltage boost module of the controller, a rate of change of the active power output; receiving, via a frequency-voltage boost function of the controller, a frequency signal representative of a grid frequency of the utility grid; determining, via the frequency -voltage boost function of the controller, a downward rate of change of the frequency signal; and in response to at least one of the rate of change of the active power output exceeding an offset or the downward rate of change of the frequency signal exceeding a ramp down rate offset, generating an overall voltage boost signal for the voltage reference.

2. The method of claim 1, wherein determining, via the power-voltage boost module of the controller, the rate of change of the active power output further comprises: calculating a derivative of the active power output that reflects the rate of change of the active power output.

3. The method of claim 2, wherein, in response to at least one of the rate of change of the active power output exceeding the offset or the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: generating a first voltage boost signal from an active power path by applying a gain and a scaling factor to the rate of change of the active power output, wherein applying the scaling factor enables boosting the voltage when the active power output exceeds a threshold.

4. The method of claim 3, further comprising limiting the first voltage boost signal by a minimum value and a maximum value and filtering the first voltage701327-WO- 1 / GECW-l 325-PCT boost signal via at least one filter having a tunable bandwidth for up and down directions.

5. The method of claim 1. wherein the frequency signal is an angular frequency signal from a phase-locked loop of the controller.

6. The method of claim 3, further comprising filtering the frequency signal to remove high-frequency content related to noise as well as fast electrical transients not related to grid frequency changes.

7. The method of claim 6, wherein determining, via the frequencyvoltage boost function of the controller, the downward rate of change of the frequency signal further comprises: calculating, via the frequency-voltage boost function of the controller, a derivative of the filtered frequency signal that reflects the downward rate of change of the frequency signal.

8. The method of claim 7, further comprising changing a sign of the derivative such that decreases in grid frequencies manifest as a positive boost in voltage.

9. The method of claim 8, further comprising determining, via the frequency -voltage boost function of the controller, whether the downward rate of change of the frequency signal exceeds the ramp down rate offset and if so, multiplying the downward rate of change of the frequency signal by a gain and applying a downward rate limit to the downward rate of change of the frequency signal to determine a second voltage boost signal from a frequency path.

10. The method of claim 9, further comprising limiting the second voltage boost signal by a minimum value and a maximum value.

11. The method of claim 9. wherein, in response to at least one of the rate of change of the active power output exceeding the offset or the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: summing the first voltage boost signal from the active power path and the second voltage boost signal from the frequency path together to determine the overall voltage boost signal.

12. The method of claim 11, further comprising limiting the overall701327-WO- 1 / GECW-l 325-PCT voltage boost signal by at least a dynamic maximum limit to minimize overvoltage conditions.

13. The method of claim 1. wherein the inverter-based resource compnses a wind turbine.

14. The method of claim 1, wherein the inverter-based resource is one of a grid-following inverter-based resource or a grid-forming inverter-based resource.

15. A system for boosting voltage at a voltage terminal of an inverterbased resource to maintain stable operation during recovery of a utility grid transient event, the inverter-based resource coupled to a utility grid, the system comprising: a controller comprising: a voltage regulator for receiving a voltage reference signal; a power-power-voltage boost module, the power-power-voltage boost module configured for receiving an active power output of the inverter-based resource and determining a rate of change of the active power output; and a frequency-voltage boost function, the frequency -voltage boost function configured for receiving a frequency signal representative of a grid frequency of the utility grid, determining a downward rate of change of the frequency signal, and in response to the rate of change of the active power output exceeding an offset and the downward rate of change of the frequency signal exceeding a ramp down rate offset, and generating an overall voltage boost signal for the voltage reference.

16. The system of claim 15, wherein determining the rate of change of the active power output further comprises: calculating a derivative of the active power output that reflects the rate of change of the active power output, and w herein, in response to the rate of change of the active power output exceeding the offset and the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: generating a first voltage boost signal from an active power path by applying a gain and a scaling factor to the rate of change of the active pow er output, wherein applying the scaling factor enables boosting the voltage when the active power output701327-WO- 1 / GECW-l 325-PCT exceeds a threshold.

17. The system of claim 16, wherein the power-power-voltage boost module is further configured to limit the first voltage boost signal by a minimum value and a maximum value and filter the first voltage boost signal via at least one filter having a tunable bandwidth for up and down directions.

18. The system of claim 16, wherein the frequency-voltage boost function is further configured to filter the frequency signal to remove high-frequency content related to noise as well as fast electrical transients not related to grid frequency changes, and wherein determining the downward rate of change of the frequency signal further comprises: calculating a derivative of the filtered frequency signal that reflects the downw ard rate of change of the frequency signal and changing a sign of the derivative such that decreases in grid frequencies manifest as a positive boost in voltage via the frequency -voltage boost function of the controller.

19. The system of claim 18, wherein the frequency-voltage boost function is further configured to multiply the own ward rate of change of the frequency signal by a gain, apply a downward rate limit to the downward rate of change of the frequency signal to determine a second voltage boost signal from a frequency path, and limit the second voltage boost signal by a minimum value and a maximum value.

20. The system of claim 19, wherein, in response to the rate of change of the active power output exceeding the offset and the downward rate of change of the frequency signal exceeding the ramp down rate offset, generating the overall voltage boost signal for the voltage reference further comprises: summing the first voltage boost signal from the active power path and the second voltage boost signal from the frequency path together to determine the overall voltage boost signal; and limiting the overall voltage boost signal by at least a dynamic maximum limit to minimize overvoltage conditions.

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