Systems and methods for frequency filtering of renewable energy power systems

Abstract

A method for controlling a renewable energy power system having at least one renewable energy asset connected with a power grid during a frequency event includes receiving, via a controller, a frequency signal of the power grid. The method also includes determining, from two or more parameters of the frequency signal, a time constant for a frequency filter assembly. Further, the method includes filtering, via the frequency filter assembly, the frequency signal using the determined time constant. Moreover, the method includes determining, using the filtered frequency signal, a power command for the at least one renewable energy asset. Additionally, the method includes controlling the at least one renewable energy asset based on the power command.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to electrical power systems, and more particularly to systems and methods for controlling an electrical power system connected with a power grid in response to frequency events using a frequency filter. BACKGROUND

[0002] Wind power is considered one of the cleanest, environmentally friendliest energy sources currently available, and wind turbines have gained increasing interest in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from the wind using known airfoil principles and transmit the kinetic energy through rotational energy in order to turn a shaft that couples the rotor blades to the gearbox, or if no gearbox is used, the shaft directly couples the rotor blades to the generator. The generator then converts the mechanical energy to electrical energy that can be deployed to a utility grid.

[0003] More particularly, during operation of a wind turbine, wind impinges on the rotor blades and the blades convert the wind energy into torque that drives mechanical rotation of a low speed shaft. The low speed shaft drives a gearbox that subsequently steps up the low rotational speed of the low speed shaft in order to drive a high speed shaft at an increased rotational speed, where the high speed shaft rotatably drives a generator rotor. In many conventional wind turbine configurations, the generator is electrically coupled to a bidirectional power converter that includes a rotor side converter (RSC) that joins, via a regulated DC link, to a line side converter (LSC). The LSC converts DC power on the DC link to AC output power that is combined with power from a generator stator to provide a multiphase power having a frequency that is substantially maintained at the frequency of a power grid bus (e.g., 50 HZ or 60 HZ). The above-described system is often referred to as a doubly-fed induction generator (DFIG) system.

[0004] When providing primary frequency response services, there are at least two concerns in maintaining grid frequency stability. First, measurable events typically occur when large generation sources or loads are offline tripped. These events are characterized by a sharp initial disturbance to the frequency along with a fast recovery of the generator response to the observed disturbance on the system. Second, when resource availability of generation sources (increasingly provided by renewable energy sources) experiences a significant increase or decrease, long-term sustained events occur during a time period that can or can not be significant in magnitude. Such events can be observed, for example, when a sustained change in wind speed or irradiance occurs in a region densely populated by renewable energy generation.

[0005] Accordingly, the requirement for primary frequency response to address the aforementioned events is becoming more prevalent in grid regulation. Trends in grid requirements have tended towards tighter deadbands around the nominal frequency, at which time generator response is implemented and towards faster reaction and settling times. These trends have resulted in renewable assets, such as wind turbine power systems, spending a significant amount of time responding to frequency events. Additionally, frequency can be difficult to measure, thereby resulting in significant noise on the control feedback.

[0006] Accordingly, an improved system and method for dynamically filtering frequency would be welcome in the art that does not impact response time to the aforementioned significant events, while also eliminating the noise that causes repeated responses from renewable assets. SUMMARY

[0007] Aspects and advantages of the application will be set forth in part in the following description, or can be obvious from the description, or can be learned through practice of the application.

[0008] In one aspect, the present disclosure is directed to a method for controlling a renewable energy power system having at least one renewable energy asset connected with a power grid during a frequency event. The method includes receiving, via a controller, a frequency signal of the power grid. The method also includes determining a time constant for a frequency filter assembly from two or more parameters of the frequency signal. Further, the method includes filtering, via the frequency filter assembly, the frequency signal using the determined time constant. Moreover, the method includes determining a power command for the at least one renewable energy asset using the filtered frequency signal. Additionally, the method includes controlling the at least one renewable energy asset based on the power command.

[0009] In an embodiment, the method can include measuring the frequency signal via one or more sensors. In another embodiment, the two or more parameters can include at least a first parameter and a second parameter. For example, in such an embodiment, the first parameter and the second parameter can depend on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of the frequency response. In a further embodiment, the parameter dependency on the frequency can further depend on whether the frequency event is a high frequency event or a low frequency event.

[0010] In a further embodiment, the method can include setting the first parameter to a magnitude dependent on a maximum observed of the frequency event, such that a response time of the renewable energy power system is reduced during the frequency event, and resetting the first parameter to an initial value only after the frequency event ends to ensure that the time constant remains fast for the duration of the frequency event.

[0011] In additional embodiments, determining a time constant for the frequency filter assembly as a function of two or more parameters of the frequency signal can include utilizing at least one of a lookup table, a function, or an algorithm.

[0012] In particular embodiments, the method can include comparing the frequency signal to a frequency threshold to determine a presence of a frequency event occurring in the power grid. In further embodiments, the frequency event can include at least one of a high frequency event, a low frequency event, or a frequency event of some duration.

[0013] In certain embodiments, the method can include resetting the time constant to a default value when the filtered frequency returns within a certain frequency deadband or threshold.

[0014] In another embodiment, the renewable energy power system can be a wind turbine power system, an energy storage system, a solar power system, or a combination thereof. Accordingly, the renewable energy asset(s) can include a wind turbine, a solar panel, an energy storage device, or a combination thereof, such as a hybrid power system.

[0015] In yet another aspect, the disclosure is directed to a method for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event. The method includes receiving, via a controller, a frequency signal of the power grid. The method also includes filtering the frequency signal via a first frequency filter having a dynamic time constant that varies as a function of a first parameter. The method can also include filtering the frequency signal via a second frequency filter having a dynamic time constant that varies as a function of a second parameter of the frequency signal. Accordingly, the method includes selecting one of the filtered frequency signals. Further, the method includes controlling the at least one renewable energy asset based on the selected filtered frequency signal. It should be appreciated that the method can further include any combination of additional features and / or steps as described herein.

[0016] In yet another aspect, the disclosure is directed to a system for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event. The system includes one or more sensors for measuring a frequency signal of the power grid, a frequency filter assembly for filtering the frequency signal, and a controller. The frequency filter assembly has a dynamic time constant. For example, the dynamic time constant varies as a function of two or more parameters of the frequency signal. Further, the controller is configured to perform a plurality of operations including, but not limited to, determining a power command for the at least one renewable energy asset using the filtered frequency signal, and controlling the at least one renewable energy asset based on the power command. It should be appreciated that the system can further include any combination of additional features and / or steps as described herein.

[0017] The present invention provides a set of technical solutions as follows.

[0018] Technical Solution 1. A method for controlling a renewable energy power system having at least one renewable energy asset connected with a power grid during a frequency event, the method comprising:

[0019] receiving a frequency signal of the power grid via a controller;

[0020] determining a time constant for a frequency filter assembly from two or more parameters of the frequency signal;

[0021] filtering the frequency signal via the frequency filter assembly using the determined time constant;

[0022] determining a power command for the at least one renewable energy asset using the filtered frequency signal; and

[0023] controlling the at least one renewable energy asset based on the power command.

[0024] Technical Solution 2. The method of Technical Solution 1, further comprising measuring the frequency signal via one or more sensors.

[0025] Technical Solution 3. The method of Technical Solution 1, wherein the two or more parameters comprise at least a first parameter and a second parameter, the first parameter and the second parameter dependent on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of a frequency response.

[0026] Technical Solution 4. The method of Technical Solution 3, further comprising setting the first parameter to a magnitude dependent on a maximum value observation of the frequency event such that a response time of the renewable energy power system is reduced during the frequency event, and resetting the first parameter to an initial value only after the frequency event ends to ensure that the time constant remains fast for a duration of the frequency event.

[0027] Technical Solution 5. The method of Technical Solution 1, wherein the frequency filter assembly comprises a hysteresis filter.

[0028] Technical Solution 6. The method of Technical Solution 1, wherein determining the time constant for the frequency filter assembly from two or more parameters of the frequency signal further comprises utilizing at least one of a lookup table, a function, or an algorithm.

[0029] TECHNICAL SOLUTION 7. The method of TECHNICAL SOLUTION 1, further comprising comparing the frequency signal to a frequency threshold to determine a presence of the frequency event occurring in the power grid.

[0030] TECHNICAL SOLUTION 8. The method of TECHNICAL SOLUTION 1, wherein the frequency event comprises at least one of a high frequency event, a low frequency event, or a frequency event of some duration.

[0031] TECHNICAL SOLUTION 9. The method of TECHNICAL SOLUTION 1, further comprising resetting the time constant to a default value when the filtered frequency returns within some frequency deadband.

[0032] TECHNICAL SOLUTION 10. The method of TECHNICAL SOLUTION 1, wherein the renewable energy power system comprises at least one of a wind turbine power system, an energy storage system, a solar power system, or a combination thereof, and wherein the at least one renewable energy asset comprises at least one of a wind turbine, a solar panel, an energy storage device, or a combination thereof.

[0033] TECHNICAL SOLUTION 11. A method for controlling a renewable energy power system having at least one renewable energy asset connected with a power grid during a frequency event, the method comprising:

[0034] receiving, via a controller, a frequency signal of the power grid;

[0035] filtering, via a first frequency filter having a dynamic time constant, the frequency signal, the dynamic time constant varying according to a first parameter; and

[0036] filtering, via a second frequency filter having a dynamic time constant, the frequency signal, the dynamic time constant varying according to a second parameter of the frequency signal;

[0037] selecting one of the filtered frequency signals; and

[0038] controlling the at least one renewable energy asset based on the selected filtered frequency signal.

[0039] TECHNICAL SOLUTION 12. A system for controlling a renewable energy power system having at least one renewable energy asset connected with a power grid during a frequency event, the system comprising:

[0040] one or more sensors for measuring a frequency signal of the power grid;

[0041] a frequency filter assembly for filtering the frequency signal, the frequency filter assembly having a dynamic time constant, the dynamic time constant varying according to two or more parameters of the frequency signal; and

[0042] a controller configured to perform a plurality of operations, the plurality of operations comprising:

[0043] determining a power command for the at least one renewable energy asset using the filtered frequency signal; and

[0044] controlling the at least one renewable energy asset based on the power command.

[0045] CLAIM 13. The system of claim 12, wherein the two or more parameters comprise at least a first parameter and a second parameter, the first parameter and the second parameter dependent on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of a frequency response.

[0046] CLAIM 14. The system of claim 13, further comprising setting the first parameter to depend on a maximum observed magnitude of the frequency event, such that a response time of the renewable energy power system is reduced during the frequency event, and resetting the first parameter to an initial value only after the frequency event has ended to ensure that the time constant remains fast for the duration of the frequency event.

[0047] CLAIM 15. The system of claim 12, wherein the frequency filter assembly comprises a hysteresis filter.

[0048] CLAIM 16. The system of claim 12, wherein the dynamic time constant is determined via at least one of a lookup table, a function, or an algorithm.

[0049] CLAIM 17. The system of claim 12, wherein the plurality of operations further comprise comparing the frequency signal to a frequency threshold to determine a presence of the frequency event occurring in the power grid.

[0050] CLAIM 18. The system of claim 12, wherein the frequency event comprises at least one of a high frequency event, a low frequency event, or a frequency event for some duration.

[0051] CLAIM 19. The system of claim 12, wherein the plurality of operations further comprise resetting the time constant to a default value when the filtered frequency returns within a certain frequency deadband.

[0052] Technical Solution 20. The system of Technical Solution 12, wherein the renewable energy power system comprises at least one of a wind turbine power system, an energy storage system, a solar power system, or a combination thereof, and wherein the at least one renewable energy asset comprises at least one of a wind turbine, a solar panel, an energy storage device, or a combination thereof.

[0053] These and other features, aspects, and advantages of the present application 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 application and serve to explain the principles of the application. BRIEF DESCRIPTION OF DRAWINGS

[0054] A complete and enabling disclosure of the application, including its best mode, directed to one of ordinary skill in the art, is set forth in the specification that follows, and is illustrated in the accompanying drawings that

[0055] Figure 1 FIG. illustrates a perspective view of one embodiment of a wind turbine in accordance with the present disclosure;

[0056] Figure 2 FIG. illustrates one embodiment of an electrical and control system that can be used with the wind turbine shown in Figure 1

[0057] Figure 3 FIG. illustrates a block diagram of one embodiment of suitable components that can be included within a controller of a wind turbine in accordance with the present disclosure;

[0058] Figure 4 FIG. illustrates a schematic diagram of one embodiment of a wind farm having a plurality of wind turbines in accordance with the present disclosure;

[0059] Figure 5 FIG. illustrates a schematic diagram of one embodiment of a system for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event in accordance with the present disclosure;

[0060] Figure 6 FIG. illustrates a flowchart of one embodiment of a method for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event in accordance with the present disclosure; and

[0061] Figure 7 FIG. illustrates a schematic diagram of one embodiment of a system for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event in accordance with the present disclosure. DETAILED DESCRIPTION

[0062] ​Reference will now be made in detail to embodiments of the application, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the application and is not meant as a limitation of the application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the scope or spirit of the application. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield still a further embodiment. Thus, it is intended that the present application covers modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

[0063] Generally, the present disclosure is directed to systems and methods for controlling a renewable energy power system (e.g., a wind turbine) connected to a power grid during a frequency event. It should be appreciated that the present disclosure can also be used for DFIG systems, full-conversion systems, battery storage systems, and / or solar inverters. More particularly, the present disclosure uses at least two factors to drive a dynamic filter applied to raw frequency feedback. In embodiments, the two factors, which can be a duration and a depth of a frequency event, can be aligned with grid stability efforts required to maintain a stable operating frequency.

[0064] In conventional systems, a fixed time constant is used to filter frequency. Further, there is a balance of requirements between response speed and the ability to suppress noise that would cause an unintended disturbance to renewable power production. Accordingly, the present disclosure introduces a dynamic dependency on at least two factors to determine how quickly to filter raw frequency feedback. For example, in embodiments, this includes determining when to apply different time constants, how variables affect the time constants, and / or when to return to a heavily filtered time constant.

[0065] Reference will now be made to the drawings, wherein Figure 1 A schematic diagram of one embodiment of a wind turbine 100 in accordance with the present disclosure is illustrated. As shown, the wind turbine 100 includes a nacelle 102 that houses a generator (not shown). The nacelle 102 can be mounted on a tower 104 (a portion of which is shown in Figure 1 ). The tower 104 can be any height that facilitates operation of the wind turbine 100 as described herein. The wind turbine 100 also includes a rotor 106 that includes a plurality of rotor blades 108 attached to a rotating hub 110. More particularly, as shown, the wind turbine 100 includes three rotor blades 108 attached to the hub 110. Alternatively, the wind turbine 100 can include any number of rotor blades 108 that facilitate operation of the wind turbine 100 as described herein. In embodiments, the wind turbine 100 can also include a gearbox 114 ( Figure 2 ) rotatably coupled to the rotor 106 and the generator 118 ( Figure 2 ).

[0066] Special reference Figure 2 It can be used with wind turbine 100 ( Figure 1 A schematic diagram of one embodiment of the electrical and control system 200 used together (shown in the diagram). As shown, rotor 106 may be further rotatably coupled to low-speed shaft 112. Low-speed shaft 112 may be coupled to step-up gearbox 114. Gearbox 114 may be configured to increase the rotational speed of low-speed shaft 112 and transmit that speed to high-speed shaft 116. In an embodiment, gearbox 114 may have a lift ratio of approximately 70:1. For example, low-speed shaft 112, coupled to gearbox 114 having a lift ratio of approximately 70:1 and rotating at approximately 20 revolutions per minute (20), generates a speed of high-speed shaft 116 having approximately 1400 rpm. Alternatively, gearbox 114 may have any lift ratio that facilitates the operation of wind turbine 100 as described herein. Moreover, alternatively, wind turbine 100 may include a direct-drive generator 118, wherein generator 118 is rotatably coupled to rotor 106 without any intermediate gearbox.

[0067] The high-speed shaft 116 is rotatably coupled to the generator 118. In an embodiment, the generator 118 may be a wound-rotor, synchronous, 60Hz, three-phase doubly-fed induction generator (DFIG) including a generator stator 120 magnetically coupled to a generator rotor 122. Alternatively, the generator 118 may be any generator of any number of phases that facilitates the operation of the wind turbine 100 as described herein.

[0068] Therefore, during operation, wind impacts rotor blades 108, and rotor blades 108 convert mechanical wind energy into torque that drives the low-speed shaft 112 to rotate mechanically via hub 110. The low-speed shaft 112 drives gearbox 114, which then increases the low rotational speed of shaft 112 to drive the high-speed shaft 116 at an increased rotational speed. The high-speed shaft 116 rotatably drives generator rotor 122, inducing a rotating magnetic field within generator rotor 122 and inducing a voltage within generator stator 120, which is magnetically coupled to generator rotor 122. Generator 118 converts the rotating mechanical energy into a sinusoidal, three-phase alternating current (AC) electrical signal in generator stator 120.

[0069] The electrical and control system 200 can also include a controller 202. In embodiments, the controller 202 can comprise a computer or other suitable processing unit. Thus, in several embodiments, the controller 202 can include suitable computer readable instructions that, when executed, configure the controller 202 to perform various different functions, such as receiving, transmitting, and / or implementing control signals. Thus, the controller 202 can generally be configured to control various operational modes (e.g., a conductive state or a non-conductive state) of one or more switches and / or components of embodiments of the electrical system 200.

[0070] As used herein, the term computer is not limited to just those 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 circuitry, and these terms are used interchangeably herein. In exemplary embodiments, the memory can include, but is not limited to, a computer-readable medium, such as a random access memory (RAM). Alternatively, a floppy disk, a compact disc - read only memory (CD-ROM), a magneto-optical disk (MOD), and / or a digital versatile disc (DVD) can also be used as the storage device. Also, in exemplary embodiments, an additional input channel can be, but is not limited to, a computer peripheral associated with an operator interface, such as a mouse and a keyboard. Alternatively, other computer peripherals can also be used, which can include, for example, but are not limited to, a scanner. Furthermore, in exemplary embodiments, an additional output channel can include, but is not limited to, an operator interface monitor.

[0071] For example, Figure 3 A block diagram of one embodiment of suitable components that can be included within any other computing device or controller 202 in accordance with aspects of the present subject matter is illustrated. As shown, the controller 202 can include one or more processors 62 and associated memory devices 64 configured to perform various computer-implemented functions (e.g., performing the methods, steps, computations and / or the like disclosed herein).

[0072] 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 controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Additionally, the memory device(s) 64 can generally include memory element(s) including, but not limited to, computer readable medium, for example random access memory (RAM), computer readable nonvolatile memory (e.g., flash memory), soft disks, compact disks - read only memory (CD-ROMs), magneto-optical disks (MODs), digital versatile disks (DVDs), and / or other appropriate memory elements. Such memory device(s) 64 can generally be configured to store appropriate computer readable instructions that, when executed by the processor(s) 62, configure the controller 202 to perform various functions including, but not limited to, directly or indirectly transmitting appropriate control signals to one or more switches including the bi-directional power conversion assembly 210, monitoring operating conditions of the electrical system 200, and various other appropriate computer-implemented functions.

[0073] Additionally, the controller 202 can also include a communication module 66 that functions to facilitate communication between the controller 202 and various components of the electrical system 200. For example, the communication module 66 can function as an interface that allows the controller 202 to transmit control signals to any component of the wind turbine and electrical system 200. Furthermore, the communication module 66 can include a sensor interface 68 (e.g., one or more analog-to-digital converters) that functions to allow signals transmitted from sensors (e.g., any of the sensors 58, 60, 252, 402) to be converted into signals that can be understood and processed by the processor 62. Alternatively, the controller 202 can be provided with appropriate computer readable instructions that, when executed by its processor(s) 62, configure the controller 202 to take various actions depending on the control mode of the wind turbine 100.

[0074] Referring back to Figure 2The generator stator 120 can be further electrically coupled to a stator synchronous switch 206 via a stator bus 208. In an exemplary embodiment, to facilitate a DFIG configuration, the generator rotor 122 is electrically coupled to a bi-directional power conversion assembly 210 via a rotor bus 212. Alternatively, the system 200 can be configured as a full power conversion system, where a full power conversion assembly similar in design and operation to the assembly 210 is electrically coupled to the stator 120 and such full power conversion assembly facilitates channeling of electrical power between the stator 120 and an electrical power transmission and distribution grid. The stator bus 208 transmits three-phase power from the stator 120 and the rotor bus 212 transmits three-phase power from the rotor 122 to the assembly 210. The stator synchronous switch 206 is electrically coupled to a main transformer circuit breaker 214 via a system bus 216.

[0075] The power conversion assembly 210 includes a rotor filter 218 electrically coupled to the rotor 122 via the rotor bus 212. The rotor filter 218 is electrically coupled to a rotor-side, bi-directional power converter 220 via a rotor filter bus 219. The rotor-side converter 220 is electrically coupled to a line-side, bi-directional power converter 222. The converters 220 and 222 can be substantially identical. The line-side converter 222 is electrically coupled to a line filter 224 and a line contactor 226 via a line-side power converter bus 223 and a line bus 225. In an embodiment, the converters 220 and 222 are configured in a three-phase, pulse width modulation (PWM) configuration including insulated gate bipolar transistor (IGBT) switching devices. Alternatively, the converters 220 and 222 can have any configuration using any switching devices that facilitate operation of the system 200 as described herein. Further, as shown, the assembly 210 is coupled in electronic data communication with the controller 202 to control operation of the converters 220 and 222.

[0076] The line contactor 226 is electrically coupled to a conversion circuit breaker 228 via a conversion circuit breaker bus 230. The circuit breaker 228 is also electrically coupled to the system circuit breaker 214 via the system bus 216 and a connection bus 232. The system circuit breaker 214 is electrically coupled to an electrical power main transformer 234 via a generator-side bus 236. The transformer 234 is electrically coupled to a grid circuit breaker 238 via a breaker-side bus 240. The grid circuit breaker 238 is connected to an electrical power transmission and distribution grid via a grid bus 242.

[0077] Still referring to Figure 2The converters 220 and 222 are electrically coupled to one another in electrical communication via a single direct current (DC) link 244. Alternatively, the converters 220 and 222 can be electrically coupled via separate and distinct DC links. The DC link 244 includes a positive rail 246, a negative rail 248, and at least one capacitor 250 coupled therebetween. Alternatively, the capacitor 250 can be one or more capacitors configured in series or in parallel between the rails 246 and 248.

[0078] In one embodiment, as shown, the system 200 can also include one or more voltage sensors 252 electrically coupled to each of the three phases of the bus 242. Alternatively, the voltage sensors 252 can be electrically coupled to the system bus 216. Also, alternatively, the voltage sensors 252 can be electrically coupled to any portion of the system 200 that facilitates operation of the system 200 as described herein.

[0079] During operation, the associated electrical power from the generator 118 is transmitted via the bus 208, the switch 206, the bus 216, the circuit breaker 214, and the bus 236 to the main transformer 234. The main transformer 234 boosts the voltage amplitude of the electrical power, and the transformed electrical power is further transmitted via the bus 240, the circuit breaker 238, and the bus 242 to the power grid.

[0080] In a doubly-fed induction generator configuration, a second electrical power transmission path is provided. For example, as shown, electrical, three-phase, sinusoidal AC power is generated within the wound rotor 122 and transmitted via the bus 212 to the assembly 210. Within the assembly 210, the electrical power is transmitted to the rotor filter 218, where the electrical power is modified for a rate of change of the PWM signals associated with the converter 220. The power converter 220 functions as a rectifier and rectifies the sinusoidal three-phase AC power into DC power. The DC power is transmitted to the DC link 244. The capacitor 250 facilitates mitigating DC link voltage amplitude variations by facilitating mitigating DC ripple associated with AC rectification.

[0081] The DC power is then transmitted from the DC link 244 to the line-side converter 222, where the converter 222 functions as an inverter configured to convert the DC electrical power from the DC link 244 into three-phase sinusoidal AC electrical power having a predetermined voltage, current, and frequency. This conversion is monitored and controlled via the controller 202. The converted AC power is transmitted from the line-side converter 222 via the bus 227 and 225, the line contactor 226, the bus 230, the circuit breaker 228, and the bus 232 to the bus 216. The line filter 224 compensates or adjusts for harmonic currents in the electrical power transmitted from the line-side converter 222. The stator synchronization switch 206 is configured to be closed so that connecting the three-phase power from the stator 120 with the three-phase power from the assembly 210 is facilitated.

[0082] Circuit breakers 228, 214, and 238 are configured to open the corresponding bus, e.g., when current flow is excessive and can damage components of system 200. Additional protection components can also be provided, including line contactors 226, which can be controlled to form a disconnect by opening switches (not shown in FIG. 2) corresponding to each of the lines in line bus 230. Figure 2

[0083] Additionally, assembly 210 can compensate or adjust the frequency of the three-phase power from rotor 122 for variations in wind speed at hub 110 and rotor blades 108, for example. Thus, in this manner, the mechanical and electrical rotor frequencies are decoupled and substantially independent of the mechanical rotor speed to facilitate electrical stator and rotor frequency matching.

[0084] Power conversion assembly 210 and generator 118 can be susceptible to grid voltage fluctuations and other forms of grid faults. Generator 118 can store magnetic energy that can be converted into high currents when the generator terminal voltage is rapidly reduced. Those currents can reduce the expected lifetime of components of assembly 210, including but not limited to semiconductor devices, such as IGBTs within converters 220 and 222.

[0085] Reference is now made to Figure 4 As shown, wind turbine 100 can be part of a wind farm 300 that includes a plurality of wind turbines 302 communicatively coupled to a wind farm controller 304 via a network 306. For example, as shown in the illustrated embodiment, wind farm 300 includes twelve wind turbines, including wind turbine 100. However, in other embodiments, wind farm 300 can include any other number of wind turbines, such as fewer than twelve wind turbines or more than twelve wind turbines. In one embodiment, controller 202 of wind turbine 100 can be communicatively coupled with wind farm controller 304 through a wired connection, such as by connecting controller 202 via an appropriate communication link, such as an appropriate cable. Alternatively, controller 202 can be communicatively coupled with wind farm controller 304 through a wireless connection, such as by using any appropriate wireless communication protocol known in the art. Additionally, wind farm controller 304 can generally be configured similarly to controllers 202 for each of the individual wind turbines 302 within wind farm 300.

[0086] ​In several embodiments, one or more of the wind turbines 302 in the wind farm 300 can include a plurality of sensors for monitoring various operational data of the individual wind turbines 302 and / or one or more environmental parameters of the wind farm 300. For example, as shown, each of the wind turbines 302 can include a wind sensor 308 configured to measure a wind speed or any other wind parameter, such as an anemometer or any other suitable device.

[0087] Referring now to Figure 5 and Figure 6 , a system 400 and method 500 for controlling a renewable energy power system, such as the wind turbine system 200, in accordance with the present disclosure is illustrated. With particular reference to Figure 5 , the system 400 includes at least one grid metering device or sensor 402 for monitoring one or more grid parameters. Thus, as shown, the grid sensor 402 is configured to generate an original frequency signal 404. In embodiments, it is the object of the present disclosure to identify when the observed original frequency signal 404 should be deeply filtered, and when such a signal should be tracked as quickly as possible in response to measurable events. Moreover, in embodiments, the system 400 can receive the original frequency signal 404 and determine when a frequency event occurs. In particular embodiments, as shown at 406, a frequency event can be identified by determining whether the original frequency signal 404 exceeds a particular threshold above or below a nominal frequency.

[0088] Thus, if the system 400 identifies a frequency event in the power grid, the original frequency signal 404, which is typically noisy, can be sent to a plurality of time constant modules 408, 410. For example, in embodiments, the time constant modules 408, 410 can include one or more algorithms programmed therein for calculating one or more parameters of the original frequency signal 404. More particularly, in one embodiment, the parameters can include a duration of the frequency event, an amplitude of the frequency event, a rate of change of the frequency response, and any other grid parameter that can affect the speed at which the original frequency signal 404 is filtered. Thus, the time constant modules 408, 410 are also configured to generate different time constants 412, 414 for the frequency filter module 416. For example, in one embodiment, the time constant modules 408, 410 can use measurements of the duration and amplitude, respectively, to determine an applicable time constant, such as using a lookup table, function, or algorithm (e.g., such as a simple MIN(x,y) function or any other suitable algorithm or mathematical function) to determine which filter time constant to use.

[0089] In certain embodiments, an important distinction of the parameter depending on the depth / duration of the event should be latched at the maximum value observed during the event. This maximum value can then be reset at the end of the frequency event, resulting in the effect that if a large event is observed, the time constant associated with the event remains fast for the duration of the event, even if the event amplitude returns to a smaller value during the event.

[0090] Still referring to Figure 5 , the system 400 includes a dynamic frequency filtering module 416 having at least one filter. Thus, once the frequency filtering time constant is determined, it can be applied to the raw frequency signal 404 using any appropriate filter in the frequency filtering module 416. For example, in an embodiment, the frequency filtering module 416 can include a low pass filter, a high pass filter, a band pass filter, a notch filter, or a combination thereof, or any other appropriate filter. Moreover, in an embodiment, the particular implementation of the filter(s) can be a lag filter, an exponential filter, a lead-lag compensator, a Kalman filter, or another other appropriate implementation.

[0091] Accordingly, in an embodiment, the frequency filtering module 416 is dynamic in that the module 416 can select an appropriate time constant based on the type of frequency event occurring in the power grid (and how quickly a response is needed). Since frequency is often difficult to measure, the raw frequency signal 404 is often very noisy, and if relied on alone, can cause too many control actions by the controller. Moreover, as grid regulation is becoming more stringent (e.g., a deadband of tens of millihertz), the dynamic frequency filtering module 416 helps to minimize the number of times the controller 202 must respond to a frequency event by more accurately filtering the raw frequency signal 404 based on the type of event. This results in less disturbance to the power generation profile, longer time periods between responses, an increase in the total amount of energy produced annually. More particularly, as shown, the output 418 of the frequency filtering module 416 (also referred to as the filtered frequency signal) can then be sent to a primary frequency response logic 420 that determines how quickly to respond to the frequency event by determining a power command 422 for each of the wind turbines 302 in the wind farm 300.

[0092] In a still further embodiment, the system 400 can determine when to reset the filter time constant to a default value. Thus, in one embodiment, the system 400 can reset the time constant when the filtered frequency signal 418 returns within the frequency deadband, which ensures that the raw frequency signal 404 is not re- deeply filtered until the filtered frequency signal 418 returns within the deadband.

[0093] In particular, with reference toFigure 6 FIG. 13 illustrates a flowchart of one embodiment of a method 1300 for controlling a renewable energy power system, such as the wind turbine power system 200. Generally, the method 1300 is described herein with reference to the wind turbine(s) 100, 302. However, it should be appreciated that the disclosed method 1300 can be implemented with any other suitably configured wind turbine. Additionally, although the method 1300 is described below for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement of steps. Those skilled in the art will appreciate from the disclosure provided herein that various steps of the methods disclosed herein can be omitted, rearranged, combined and / or adapted in various ways without departing from the scope of the present disclosure. Figures 1-5 Figure 6 For the purposes of illustration and discussion, steps are depicted as being performed in a particular order. The methods discussed herein are not limited to any particular order or arrangement of steps. Those skilled in the art will appreciate from the disclosure provided herein that various steps of the methods disclosed herein can be omitted, rearranged, combined and / or adapted in various ways without departing from the scope of the present disclosure.

[0094] As shown at (502), the method 500 includes measuring and receiving a frequency signal of a power grid (e.g., at a point of regulation). As shown at (504), the method 500 can include comparing the frequency signal to a frequency threshold to determine the presence of a frequency event occurring in the power grid. In certain embodiments, for example, the frequency event can include a high frequency event, a low frequency event, or a frequency event of some duration. If the frequency signal indicates a frequency event occurring in the power grid, the method continues at (506) and (508). More particularly, in embodiments, the method 500 can include determining a time constant for a frequency filter assembly from two or more parameters of the frequency signal. In certain embodiments, the two or more parameters can include at least a first parameter and a second parameter. For example, as described at (506) and (508), the method 500 includes determining the first parameter and the second parameter from an event magnitude and an event duration, respectively.

[0095] As shown at (510), the method 500 includes determining a time constant for a frequency filter assembly from the first and second parameters of the frequency signal. As shown at (512), the method 500 includes filtering the frequency signal using the determined time constant via the frequency filter assembly. As shown at (514), the method 500 includes determining a power command for at least one renewable energy asset (e.g., one of the wind turbines 302 described herein) using the filtered frequency signal. As shown at (516), the method 500 includes controlling the renewable energy asset(s) based on the power command.

[0096] In certain embodiments, the method 500 can also include resetting the time constant to a default value when the filtered frequency returns within a certain frequency deadband.

[0097] Reference is now made to Figure 7 ​FIG. 6 illustrates a schematic diagram of another embodiment of a system 600 for controlling a renewable energy power system (e.g., wind turbine power system 200) in accordance with the present disclosure. More particularly, as shown, system 600 includes at least one grid metering device or sensor 602 for monitoring one or more grid parameters. Thus, as shown, grid sensor 602 is configured to generate a raw frequency signal 604. In embodiments, as noted, system 600 is configured to identify when an observed raw frequency signal 604 should be deeply filtered, and when such a signal should be tracked as quickly as possible in response to a measurable event. Further, in embodiments, system 600 can receive raw frequency signal 604 and determine when a frequency event occurs. In particular embodiments, as shown at 606, a frequency event can be identified by determining whether raw frequency signal 604 exceeds a particular threshold above or below a nominal frequency.

[0098] Thus, if system 600 identifies a frequency event in the power grid, raw frequency signal 604 (which is typically noisy) can be sent to a plurality of time constant modules 608, 610. For example, in embodiments, time constant modules 608, 610 can include one or more algorithms programmed therein for calculating one or more parameters of raw frequency signal 604. More particularly, in one embodiment, parameters can include a duration of the frequency event, an amplitude of the frequency event, a rate of change of the frequency response, and any other grid parameters that can affect the speed at which raw frequency signal 604 is filtered. Thus, time constant modules 608, 610 are also configured to generate different time constants 612, 614 for frequency filtering logic modules 616, 618 described herein below. For example, in one embodiment, time constant modules 608, 610 can use measurements of duration and amplitude, respectively, to determine an applicable time constant, e.g., using a lookup table, function, or algorithm (e.g., such as a simple MIN(x,y) function or any other appropriate algorithm or mathematical function) to determine which filter time constant to use.

[0099] Once the frequency filter time constants 612, 614 are determined, they can be applied to the raw frequency signal 604, for example using any appropriate filter in the frequency filter logic modules 616, 618. For example, in embodiments, the frequency filter logic modules 616, 618 can include a low pass filter, a high pass filter, a band pass filter, a notch filter, or a combination thereof or any other appropriate filter. Further, in embodiments, the particular implementation of the filter(s) can be a lag filter, an exponential filter, a lead-lag compensator, a Kalman filter, or another other appropriate implementation. The filtered frequency values 620, 622 can then be sent to a frequency feedback selection module 624, which is configured to select one of the filtered frequency values 620, 622, i.e., depending on the expected response time required for a frequency event. The output 626 of the frequency feedback selection module 624 can then be sent to a primary frequency response logic 628, which determines how quickly to respond to a frequency event by determining a power command 630 for each of the wind turbines 302 in the wind farm 300.

[0100] As described above, and as will be appreciated by those skilled in the art, embodiments of the present application can be configured as a system, method, or computer program product. Accordingly, embodiments of the present application can be comprised of various means including entirely hardware, entirely software, or any combination of software and hardware. Furthermore, embodiments of the present application can take the form of a computer program product on a computer-readable storage medium having computer readable program instructions (e.g., computer software) embodied in the computer-readable storage medium. Any suitable non-transitory computer readable storage medium can be utilized including a hard disk, CD-ROM, optical storage device, or magnetic storage device.

[0101] Embodiments of the present application are described above with reference to block and flow diagrams of methods, apparatus (i.e., systems) and computer program products according to this application. It will be understood that each block of the block and flow diagrams, and combinations of blocks in the block and flow diagrams, can be implemented by various means, including computer program instructions. These computer program instructions can be loaded onto a general purpose computer, a special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions which execute on the computer or other programmable data processing apparatus create means for implementing the functions specified in the flowchart block or blocks.

[0102] These computer program instructions can also be stored in a non-transitory computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including computer-readable instructions for implementing the functionality specified in the flow diagram block or blocks. The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that are executed on the computer or other programmable apparatus provide steps for implementing the functions specified in the flow diagram block or blocks.

[0103] Further aspects of the application are provided by the subject matter of the following clauses:

[0104] Clause 1. A method for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event, the method comprising:

[0105] receiving, via a controller, a frequency signal of the power grid;

[0106] determining, from two or more parameters of the frequency signal, a time constant for a frequency filter assembly;

[0107] filtering, via the frequency filter assembly, the frequency signal using the determined time constant;

[0108] determining, using the filtered frequency signal, a power command for the at least one renewable energy asset; and

[0109] controlling the at least one renewable energy asset based on the power command.

[0110] Clause 2. The method of Clause 1, further comprising measuring, via one or more sensors, the frequency signal.

[0111] Clause 3. The method of any preceding clause, wherein the two or more parameters include at least a first parameter and a second parameter, the first and second parameters depending on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of a frequency response.

[0112] Clause 4. The method of any preceding clause, further comprising setting the first parameter to a magnitude dependent on a maximum value observation of the frequency event, such that a response time of the renewable energy power system is reduced during the frequency event, and resetting the first parameter to an initial value only after the frequency event ends to ensure that the time constant remains fast for a duration of the frequency event.

[0113] Clause 5. The method of any preceding clause, wherein the frequency filter assembly comprises a lag filter.

[0114] Clause 6. The method of any preceding clause, wherein determining the time constant for the frequency filter assembly as a function of two or more parameters of the frequency signal further comprises utilizing at least one of a lookup table, a function, or an algorithm.

[0115] Clause 7. The method of any preceding clause, further comprising comparing the frequency signal to a frequency threshold to determine a presence of the frequency event occurring in the power grid.

[0116] Clause 8. The method of any preceding clause, wherein the frequency event comprises at least one of a high frequency event, a low frequency event, or a frequency event for some duration of time.

[0117] Clause 9. The method of any preceding clause, further comprising resetting the time constant to a default value when the filtered frequency returns within a certain frequency deadband.

[0118] Clause 10. The method of any preceding clause, wherein the renewable energy power system comprises at least one of a wind turbine power system, an energy storage system, a solar power system, or a combination thereof, and wherein the at least one renewable energy asset comprises at least one of a wind turbine, a solar panel, an energy storage device, or a combination thereof.

[0119] Clause 11. A method for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event, the method comprising:

[0120] receiving, via a controller, a frequency signal of the power grid;

[0121] filtering the frequency signal via a first frequency filter having a dynamic time constant that varies as a function of a first parameter; and

[0122] filtering the frequency signal via a second frequency filter having a dynamic time constant that varies as a function of a second parameter of the frequency signal;

[0123] selecting one of the filtered frequency signals; and

[0124] controlling the at least one renewable energy asset based on the selected filtered frequency signal.

[0125] Clause 12. A system for controlling a renewable energy power system having at least one renewable energy asset connected with a power grid during a frequency event, the system comprising:

[0126] one or more sensors for measuring a frequency signal of the power grid;

[0127] a frequency filter assembly for filtering the frequency signal, the frequency filter assembly having a dynamic time constant that varies as a function of two or more parameters of the frequency signal; and

[0128] a controller configured to perform a plurality of operations, the plurality of operations comprising:

[0129] determining a power command for the at least one renewable energy asset using the filtered frequency signal; and

[0130] controlling the at least one renewable energy asset based on the power command.

[0131] Clause 13. The system of Clause 12, wherein the two or more parameters include at least a first parameter and a second parameter, the first and second parameters depending on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of a frequency response.

[0132] Clause 14. The system of Clauses 12-13, further comprising setting the first parameter to depend on a maximum observed magnitude of the frequency event, such that a response time of the renewable energy power system is reduced during the frequency event, and resetting the first parameter to an initial value only after the frequency event ends to ensure that the time constant remains fast for the duration of the frequency event.

[0133] Clause 15. The system of Clauses 12-14, wherein the frequency filter assembly comprises a hysteresis filter.

[0134] Clause 16. The system of Clauses 12-15, wherein the dynamic time constant is determined via at least one of a lookup table, a function, or an algorithm.

[0135] Clause 17. The system of Clauses 12-16, wherein the plurality of operations further comprise comparing the frequency signal to a frequency threshold to determine a presence of the frequency event occurring in the power grid.

[0136] Clause 18. The system of Clauses 12-17, wherein the frequency event comprises at least one of a high frequency event, a low frequency event, or a frequency event for some duration.

[0137] Clause 19. The system of clauses 12-18, wherein the plurality of operations further comprise resetting the time constant to a default value when the filtered frequency returns within a certain frequency deadband.

[0138] Clause 20. The system of clauses 12-19, wherein the renewable energy power system comprises at least one of a wind turbine power system, an energy storage system, a solar power system, or a combination thereof, and wherein the at least one renewable energy asset comprises at least one of a wind turbine, a solar panel, an energy storage device, or a combination thereof.

[0139] 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 can 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 have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

1. A method for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event, the method comprising: receiving, via a controller, a frequency signal of the power grid; determining a time constant for a frequency filter assembly from two or more parameters of the frequency signal; filtering, via the frequency filter assembly, the frequency signal using the determined time constant; determining a power command for the at least one renewable energy asset using the filtered frequency signal; and controlling the at least one renewable energy asset based on the power command, wherein the two or more parameters include at least a first parameter and a second parameter, the first parameter and the second parameter dependent on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of a frequency response, the first parameter set to a magnitude dependent on a maximum observed value of the frequency event such that a response time of the renewable energy power system is reduced during the frequency event.

2. The method of claim 1, further comprising measuring the frequency signal via one or more sensors.

3. The method of claim 1, further comprising resetting the first parameter to an initial value only after the frequency event ends to ensure that the time constant remains fast for the duration of the frequency event. the frequency filter assembly comprises a hysteresis filter.

4. The method of claim 1, wherein, determining the time constant for the frequency filter assembly from two or more parameters of the frequency signal further comprises utilizing at least one of a lookup table, a function, or an algorithm.

5. The method of claim 1, wherein, 6. The method of claim 1, further comprising comparing the frequency signal to a frequency threshold to determine a presence of the frequency event occurring in the power grid. the frequency event comprises at least one of a high frequency event, a low frequency event, or a frequency event of some duration.

7. The method of claim 1, wherein, 8. The method of claim 1, further comprising resetting the time constant to a default value when the filtered frequency returns within some frequency deadband. the renewable energy power system comprises at least one of a wind turbine power system, an energy storage system, a solar power system, or a combination thereof, and wherein the at least one renewable energy asset comprises at least one of a wind turbine, a solar panel, an energy storage device, or a combination thereof.

9. The method of claim 1, wherein, 10. A method for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event, the method comprising: receiving, via a controller, a frequency signal of the power grid; filtering, via a first frequency filter having a dynamic time constant, the frequency signal, the dynamic time constant varying according to a first parameter; and filtering, via a second frequency filter having a dynamic time constant, the frequency signal, the dynamic time constant varying according to a second parameter of the frequency signal; selecting one of the filtered frequency signals; and controlling the at least one renewable energy asset based on the selected filtered frequency signal, ​ ​ wherein the first parameter and the second parameter depend on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of a frequency response, the first parameter is set to depend on a magnitude of a maximum observation of the frequency event, such that a response time of the renewable energy power system is reduced during the frequency event.

11. A system for controlling a renewable energy power system having at least one renewable energy asset connected to a power grid during a frequency event, the system comprising: one or more sensors for measuring a frequency signal of the power grid; a frequency filter assembly for filtering the frequency signal, the frequency filter assembly having a dynamic time constant that varies according to two or more parameters of the frequency signal; and a controller configured to perform a plurality of operations, the plurality of operations comprising: determining a power command for the at least one renewable energy asset using the filtered frequency signal; and controlling the at least one renewable energy asset based on the power command, wherein the two or more parameters include at least a first parameter and a second parameter, the first parameter and the second parameter depend on at least one of a magnitude of the frequency event, a duration of the frequency event, or a rate of change of a frequency response, the first parameter is set to depend on a magnitude of a maximum observation of the frequency event, such that a response time of the renewable energy power system is reduced during the frequency event.

12. The system of claim 11, further comprising resetting the first parameter to an initial value only after the frequency event ends to ensure that the time constant remains fast for the duration of the frequency event.

13. The system of claim 11, wherein, the frequency filter assembly comprises a hysteresis filter.

14. The system of claim 11, wherein, the dynamic time constant is determined via at least one of a lookup table, a function, or an algorithm.

15. The system of claim 11, wherein, the plurality of operations further comprise comparing the frequency signal to a frequency threshold to determine a presence of the frequency event occurring in the power grid.

16. The system of claim 11, wherein, the frequency event comprises at least one of a high frequency event, a low frequency event, or a frequency event for some duration.

17. The system of claim 11, wherein, the plurality of operations further comprise resetting the time constant to a default value when the filtered frequency returns within a certain frequency deadband.

18. The system of claim 11, wherein, the renewable energy power system comprises at least one of a wind turbine power system, an energy storage system, a solar power system, or a combination thereof, and wherein the at least one renewable energy asset comprises at least one of a wind turbine, a solar panel, an energy storage device, or a combination thereof.

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