WO2024107191A1

WO2024107191A1 - System and method for controlling a wind turbine

Info

Publication number: WO2024107191A1
Application number: PCT/US2022/050192
Authority: WO
Inventors: Arvind Kumar Tiwari; Veena Padmarao; Rupam BASAK; Apoorva Anil Sohani; Soumyashree BISOYI
Original assignee: General Electric Renovables Espana S.L.
Priority date: 2022-11-17
Filing date: 2022-11-17
Publication date: 2024-05-23

Abstract

A system and method are provided for controlling a wind turbine. A controller of the wind turbine detects a transient grid event and generates a first torque command via a drive‑train‑damper control module. The first torque command is configured to damp a torsional vibration resulting from the transient grid event. The controller also generates a second torque command via the drive-train-damper control module of the controller in response to the transient grid event. The second torque command is configured to minimize an error magnitude of power supplied to the power grid during a recovery phase immediately after the transient grid event. The controller further drives the generator to provide a first torque based on the first torque command for a first time period and drives the generator to provide a second torque based on the second torque command for a second time period.

Description

SYSTEM AND METHOD FOR CONTROLLING A WIND TURBINE

FIELD

[0001] The present disclosure relates in general to wind turbines, and more particularly to systems and methods for controlling wind turbines in response to a transient grid event.

BACKGROUND

[0002] Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The nacelle includes a rotor assembly coupled to the gearbox and to the generator. The rotor assembly and the gearbox are mounted on a bedplate support frame located within the nacelle. The one or more rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy and the electrical energy may be transmitted to a converter and/or a transformer housed within the tower and subsequently deployed to a utility grid. Modem wind power generation systems typically take the form of a wind farm having multiple such wind turbine generators that are operable to supply power to a transmission system providing power to a power grid.

[0003] In order to supply power to the power grid, wind turbines generally need to conform to certain grid requirements. For example, wind turbines may be required to offer fault-ride through (e.g. low-voltage ride through) capability. This requirement may mandate that a wind turbine stay connected to the power grid during one or more transient grid events, such as a grid fault. As used herein, the terms “grid fault,” “fault,” or similar are intended to cover a change in the magnitude of a grid voltage for a certain time duration. For example, when a grid fault occurs, the voltage of the system can decrease by a significant portion for a short duration (e.g., typically less than 500 milliseconds). In addition, grid faults may occur for variety of reasons, including but not limited to a phase conductor being connected to a ground (i.e. a ground fault), short-circuiting between phase conductors, lightning and/or windstorms, and/or accidental transmission line grounding.

[0004] In the past, the wind turbine may have been immediately disconnected in response to the voltage reduction, but as the power production of the wind turbines has increased as a percentage of the power of the power grid, the desirability for the wind turbines to remain online and ride through the transient grid events has increased. However, the voltage reduction of the transient grid event may result in the torque of the generator being significantly reduced while the rotational speed of the rotor may remain essentially unchanged. As such, when the voltage returns to pre-fault levels, a mismatch between the torque of the generator and the inertia of the rotor may result in undesirable torsional vibrations in the drivetrain of the wind turbine. The torsional vibrations may negatively impact the lifecycle of various components of the wind turbine and/or may manifest as oscillations in the power produced by the wind turbine which exceed certain power grid limits. For example, the torsional vibrations may exceed a release threshold of the slip coupling resulting in the operable decoupling of the rotor from the generator.

[0005] Thus, the art is continuously seeking new and improved systems and methods that address the aforementioned issues. As such, the present disclosure is directed to systems and methods for controlling a wind turbine to manage torsional vibration resulting from a transient grid event as well as oscillations in the power output of the wind turbine in response to the transient grid event.

BRIEF DESCRIPTION

[0006] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0007] In one aspect, the present disclosure is directed to a method for controlling a wind turbine. The wind turbine may be coupled to a power grid. The wind turbine may have a drivetrain which includes a rotor rotatably coupled to a generator via a slip coupling. The method may include detecting, via a controller, a transient grid event. Additionally, the method may include generating one or more torque commands via a drive-train-damper control module of the controller in response to the transient grid event. Further, the method may include driving the generator to provide torque based on the one or more torque commands. As a result of driving the generator to provide torque based on the one or more torque commands, a torsional vibration resulting from the transient grid event is damped and an error magnitude of power supplied to the power grid during a recovery phase after the transient grid event is minimized.

[0008] In another aspect, the present disclosure is directed to a system for controlling a wind turbine. The system may include a generator rotatably coupled to a rotor via a slip coupling and a controller communicatively coupled to the generator. The controller may include at least one processor configured to perform a plurality of operations. The plurality of operations may include any of the operations and/or features described herein.

[0009] 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

[0010] 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:

[0011] FIG. 1 illustrates a perspective view of one embodiment of a wind turbine according to the present disclosure;

[0012] FIG. 2 illustrates a perspective, internal view of one embodiment of a nacelle of the wind turbine according to the present disclosure;

[0013] FIG. 3 illustrates a schematic diagram of one embodiment of a drivetrain of the wind turbine according to the present disclosure;

[0014] FIG. 4 illustrates a schematic diagram of one embodiment of an electrical system for use with the wind turbine according to the present disclosure;

[0015] FIG. 5 illustrates a block diagram of one embodiment of a controller for use with the wind turbine according to the present disclosure;

[0016] FIG. 6 illustrates a graphical representation of damped torsional vibration according to the present disclosure;

[0017] FIG. 7 illustrates a graphical representation of damped power oscillation according to the present disclosure; and

[0018] FIG. 8 illustrates a flow chart diagram of one embodiment of a method for controlling a wind turbine according to the present disclosure.

[0019] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

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 one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. [0021] As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component or step from another and are not intended to signify location or importance of the individual components or sequence of the individual steps.

[0022] The terms “coupled,” “fixed,” “attached to,” and the like refer to both direct coupling, fixing, or attaching, as well as indirect coupling, fixing, or attaching through one or more intermediate components or features, unless otherwise specified herein.

[0023] Approximating language, as used herein throughout the specification and claims, is applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately,” “generally,” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value, or the precision of the methods or machines for constructing or manufacturing the components and/or systems. For example, the approximating language may refer to being within a 10 percent margin. [0024] Here and throughout the specification and claims, range limitations are combined and interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

[0025] Generally, the present disclosure is directed to systems and methods for controlling a wind turbine so as to increase the effectiveness of a drive-train-damper (DTD) control system with respect to both damping torsional vibrations resulting from a transient grid event and reducing oscillations in the electrical power delivered to the power grid by the wind turbine following the transient grid event, such as during a recovery phase immediately following the transient grid event, e.g., where the recovery phase begins immediately after the transient gird event and continues until the grid power stabilizes. Typically, wind turbines counter the torque generated by the rotor in response to the wind with a torque generated by the generator. Many modem wind turbines employ generators, such as a doubly -fed induction generator (DFIG), which utilize grid power for the generation of the generator torque. At the outset of a transient grid event, such as a low-voltage ride through (LVRT) event, the grid power may suddenly decrease resulting in a corresponding decrease in the generator torque. However, due to inertia and/or the effects of the wind, the rotor may continue rotating at the same speed and may, in some instances, accelerate when the rotation is not significantly resisted by the generator torque. When a transient grid event concludes, and the grid power returns, the generator may rapidly resume developing generator torque in order to return the wind turbine to a power-producing state. However, within the drivetrain of the wind turbine, the generator torque may encounter the torque resulting from the rotation of the rotor. This encounter may develop a torsional vibration within the drivetrain. A DTD control system may be employed to rapidly damp the resultant torsional vibration. Such rapid damping may, however, also result in a longer post-transient grid event recovery period and greater oscillations in the grid power during the recovery period. The present disclosure may vary the damping level applied to the torsional vibration over time throughout the recovery period in order to balance reduction of the structural loads on the drivetrain and reduction in the oscillatory nature of the power recovery. Therefore, the systems and methods of the present disclosure may increase the effectiveness of the DTD control system.

[0026] Referring now to the drawings, FIG. 1 illustrates a perspective view of one embodiment of a wind turbine 100 according to the present disclosure. As shown, the wind turbine 100 generally includes a tower 102 extending from a support surface 104, a nacelle 106, mounted on the tower 102, and a rotor 108 coupled to the nacelle 106. The rotor 108 includes a rotatable hub 110 and at least one rotor blade 112 coupled to and extending outwardly from the hub 110. For example, in the illustrated embodiment, the rotor 108 includes three rotor blades 112. However, in an alternative embodiment, the rotor 108 may include more or less than three rotor blades 112. Each rotor blade 112 may be spaced about the hub 110 to facilitate rotating the rotor 108 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub 110 may be rotatably coupled to an electric generator 118 (FIG. 2) of an electrical system 150 (FIG. 2) positioned within the nacelle 106 to permit electrical energy to be produced. [0027] The wind turbine 100 may also include a controller 200 centralized within the nacelle 106. However, in other embodiments, the controller 200 may be located within any other component of the wind turbine 100 or at a location outside the wind turbine. Further, the controller 200 may be communicatively coupled to any number of the components of the wind turbine 100 in order to control the components. As such, the controller 200 may include a computer or other suitable processing unit. Thus, in several embodiments, the controller 200 may include suitable computer-readable instructions that, when implemented, configure the controller 200 to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals. For example, such instructions may include instructions which cause the controller 200 to perform or carry out operations such as one or more method steps, such as steps of the exemplary methods described herein. Thus, it should be noted that controllers 200 as disclosed herein are capable of and may be operable to perform any methods and associated method steps as disclosed herein.

[0028] Referring now to FIGS. 2-4, a simplified, internal view of one embodiment of the nacelle 106, a schematic diagram of one embodiment of a drivetrain 146, and an exemplary electrical system 150 of the wind turbine 100 shown in FIG. 1 are illustrated. As shown, the generator 118 may be coupled to the rotor 108 for producing electrical power from the rotational energy generated by the rotor 108. For example, as shown in the illustrated embodiment, the rotor 108 may include a rotor shaft 122 coupled to the hub 110 for rotation therewith. The rotor shaft 122 may be rotatably supported by a main bearing 144. The rotor shaft 122 may, in turn, be rotatably coupled to a high-speed shaft 124 of the generator 118 through an optional gearbox 126 connected to a bedplate support frame 136 by one or more torque arms 142. As is generally understood, the rotor shaft 122 may provide a low-speed, high-torque input to the gearbox 126 in response to rotation of the rotor blades 112 and the hub 110. The gearbox 126 may then be configured with a plurality of gears 148 to convert the low-speed, high-torque input to a high-speed, low-torque output to drive the high-speed shaft 124 and, thus, the generator 118. In an embodiment, the gearbox 126 may be configured with multiple gear ratios so as to produce varying rotational speeds of the high-speed shaft for a given low-speed input, or vice versa. [0029] In an embodiment, the rotor 108 may be slowed via a torque generated by the generator 118. As the generator 118 may generate a torque counter to the rotation of the rotor 108, the high-speed shaft 124 may be equipped with a slip coupling 154. The slip coupling 154 may prevent damage to a component of the drivetrain 146 due to overloading of the drivetrain 146. As such, the slip coupling 154 may have a release threshold, or traction, above which the slip coupling 154 may permit first and second portions 162, 164 of the high-speed shaft 124 to have a different rotational speeds. It should be appreciated that, if the torsional moment at the slip coupling 154 exceeds the release/traction threshold, the generator 118 may be communicatively decoupled from the rotor 108. In such an event, the torque developed by the generator 118 may be unavailable to slow the rotor 108 or an increased rotational speed of the rotor 108 may be unavailable for increased power production.

[0030] Each rotor blade 112 may also include a pitch control mechanism 120 configured to rotate the rotor blade 112 about its pitch axis 116. Each pitch control mechanism 120 may include a pitch drive motor 128 (e.g., any suitable electric, hydraulic, or pneumatic motor), a pitch drive gearbox 130, and a pitch drive pinion 132. In such embodiments, the pitch drive motor 128 may be coupled to the pitch drive gearbox 130 so that the pitch drive motor 128 imparts mechanical force to the pitch drive gearbox 130. Similarly, the pitch drive gearbox 130 may be coupled to the pitch drive pinion 132 for rotation therewith. The pitch drive pinion 132 may, in turn, be in rotational engagement with a pitch bearing 134 coupled between the hub 110 and a corresponding rotor blade 112 such that rotation of the pitch drive pinion 132 causes rotation of the pitch bearing 134. Thus, in such embodiments, rotation of the pitch drive motor 128 drives the pitch drive gearbox 130 and the pitch drive pinion 132, thereby rotating the pitch bearing 134 and the rotor blade(s) 112 about the pitch axis 116. Similarly, the wind turbine 100 may include one or more yaw drive mechanisms 138 communicatively coupled to the controller 200, with each yaw drive mechanism(s) 138 being configured to change the angle of the nacelle 106 relative to the wind (e.g., by engaging ayaw bearing 140 of the wind turbine 100).

[0031] Referring particularly to FIG. 2, in an embodiment, the wind turbine 100 may include at least one operational sensor 158. The operational sensor(s) 158 may be configured to detect a performance of the wind turbine 100, e.g. in response to the environmental condition. For example, the operational sensor(s) 158 may be a rotational speed sensor operably coupled to the controller 200. The operational sensor(s) 158 may be directed at the rotor shaft 122 of the wind turbine 100 and/or the generator 118. The operational sensor(s) 158 may gather data indicative of the rotational speed and/or rotational position of the rotor shaft 122, and thus the rotor 108 in the form of a rotor speed and/or a rotor azimuth. The operational sensor(s) 158 may, in an embodiment, be an analog tachometer, a D.C. tachometer, an A.C. tachometer, a digital tachometer, a contact tachometer a non-contact tachometer, or a time and frequency tachometer. In an embodiment, the operational sensor(s) 158 may, for example, be an encoder, such as an optical encoder. In an embodiment, the operational sensor(s) 158 may be configured to monitor operating parameters 338 of wind turbine 100, for example, the operational sensor(s) 158 may be configured to monitor a plurality of electrical conditions, such as slip, stator voltage and current, rotor voltage and current, and line-side voltage and current at each of three phases of power.

[0032] Further, in an embodiment, the wind turbine 100 may include, or be operably coupled to, at least one grid sensor 160 configured to monitor at least one parameter of the power of the power grid 179. For example, the grid sensor(s) 160 may be configured to continuously monitor the voltage of the power grid 179 as seen by the wind turbine 100. Accordingly, the grid sensor(s) 160 may, in an embodiment, be an ammeter, a voltmeter, an ohmmeter, and/or any other suitable sensor for monitoring the power of the power grid 179.

[0033] It should also be appreciated that, as used herein, the term “monitor” and variations thereof indicates that the various sensors of the wind turbine 100 may be configured to provide a direct measurement of the parameters being monitored or an indirect measurement of such parameters. Thus, the sensors described herein may, for example, be used to generate signals relating to the parameter being monitored, which can then be utilized by the controller 200 to determine a condition or response of the wind turbine 100.

[0034] Referring particularly to FIG. 4, in an embodiment, the electrical system 150 may include various components for converting the kinetic energy of the rotor 108 into an electrical output in an acceptable form to a connected power grid 179. For example, in an embodiment, the generator 118 may be a doubly-fed induction generator (DFIG) having a stator 117 and a generator rotor 119. The generator 118 may be coupled to a stator bus 166 and a power converter 168 via a rotor bus 170. In such a configuration, the stator bus 166 may provide an output multiphase power (e.g. three-phase power) from a stator of the generator 118, and the rotor bus 170 may provide an output multiphase power (e.g. three-phase power) of the generator rotor 119 of the generator 118. Additionally, the generator 118 may be coupled via the rotor bus 170 to a rotor side converter 172. The rotor side converter 172 may be coupled to a line side converter 174 which, in turn, may be coupled to a line side bus 176. [0035] In an embodiment, the rotor side converter 172 and the line side converter 174 may be configured for normal operating mode in a three-phase, pulse width modulation (PWM) arrangement using insulated gate bipolar transistors (IGBTs) as switching devices. Other suitable switching devices may be used, such as insulated gate commuted thyristors, MOSFETs, bipolar transistors, silicone controlled rectifier’s, and/or other suitable switching devices. The rotor side converter 172 and the line side converter 174 may be coupled via a DC link 173 across which may be a DC link capacitor 175.

[0036] In an embodiment, the power converter 168 may be coupled to the controller 200 configured as a converter controller 202 to control the operation of the power converter 168. For example, the converter controller 202 may send control commands to the rotor side converter 172 and the line side converter 174 to control the modulation of switching elements used in the power converter 168 to establish a desired generator torque setpoint and/or power output.

[0037] As further depicted in FIG. 4, the electrical system 150 may, in an embodiment, include a transformer 178 coupling the wind turbine 100 to a power grid 179. The transformer 178 may, in an embodiment, be a 3-winding transformer which includes a high voltage (e.g. greater than 12 KVAC) primary winding 180. The high voltage primary winding 180 may be coupled to the power grid 179. The transformer 178 may also include a medium voltage (e.g. 6 KVAC) secondary winding 182 coupled to the stator bus 166 and a low voltage (e.g. 575 VAC, 690 VAC, etc.) auxiliary winding 184 coupled to the line bus 176. It should be appreciated that the transformer 178 can be a three-winding transformer as depicted, or alternatively, may be a two-winding transformer having only a primary winding 180 and a secondary winding 182; may be a four- winding transformer having a primary winding 180, a secondary winding 182, and auxiliary winding 184, and an additional auxiliary winding; or may have any other suitable number of windings.

[0038] In an embodiment, the electrical system 150 may also include various circuit breakers, fuses, contactors, and other devices to control and/or protect the various components of the electrical system 150. For example, the electrical system 150 may, in an embodiment, include a grid circuit breaker 188, a stator bus circuit breaker 190, and/or a line bus circuit breaker 192. The circuit breaker(s) 188, 190, 192 of the electrical system 150 may connect or disconnect corresponding components of the electrical system 150 when a condition of the electrical system 150 approaches an operational threshold of the electrical system 150.

[0039] Referring still to FIG. 4 and also to FIG. 5, embodiments of a system 300 for controlling the wind turbine 100 according to the present disclosure are presented. As shown particularly in FIG. 5, a schematic diagram of one embodiment of suitable components that may be included within the system 300 is illustrated. For example, as shown, the system 300 may include the controller 200 communicatively coupled to the operational sensor(s) 158 and the grid sensor(s) 160. Further, as shown, the controller 200 includes one or more processor(s) 206 and associated memory device(s) 208 configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like and storing relevant data as disclosed herein). Additionally, the controller 200, may also include a communications module 210 to facilitate communications between the controller 200, and the various components of the wind turbine 100. Further, the communications module 210 may include a sensor interface 212 (e.g., one or more analog-to-digital converters) to permit signals transmitted from the sensor(s) 158, 160 to be converted into signals that can be understood and processed by the processors 206. It should be appreciated that the sensor(s) 158, 160 may be communicatively coupled to the communications module 210 using any suitable means. For example, the sensor(s) 158, 160 may be coupled to the sensor interface 212 via a wired connection.

However, in other embodiments, the sensor(s) 158, 160 may be coupled to the sensor interface 212 via a wireless connection, such as by using any suitable wireless communications protocol known in the art. Additionally, the communications module 210 may also be operably coupled to an operating state control module 214 configured to change at least one wind turbine operating state. The controller 200 may further include a drivetrain damper control module 216, e.g., whereby the controller 200 may generate a torque command in response to a transient grid event via the drivetrain damper control module 216.

[0040] As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) 208 may generally comprise memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) 208 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 206, configure the controller 200 to perform various functions including, but not limited to, any of the exemplary methods and method steps as described herein, as well as various other suitable computer-implemented functions.

[0041] FIGS. 6 and 7 illustrate exemplary oscillations throughout a recovery period or recovery phase of a wind turbine following a transient grid event, e.g., low- voltage fault, etc. Numerical values are provided in FIGS. 6 and 7 solely by way of illustration to inform the examples depicted therein and such quantities are in no way intended to be limiting of the present subject matter in any respect.

[0042] Referring now specifically to FIG. 6, exemplary graphs of possible drivetrain loads in a wind turbine drivetrain over time during a recovery from a transient grid event, e.g., during a recovery phase immediately following the transient grid event, are illustrated. In FIG. 6, a first oscillatory drive train load 1000 (e.g., during a first recovery phase following a first transient grid event) and a second oscillatory drive train load 1001 (e.g., during a second recovery phase following a second transient grid event) are illustrated, as examples of varying oscillatory drive train loads in various recovery phases and various possible degrees of damping of the oscillations of the drivetrain load in the various possible recovery phases. The characteristics of the oscillatory drive train load in each recovery phase, e.g., first oscillatory drive train load 1000, second oscillatory drive train load 1001, and/or other possible oscillatory drive train loads in other possible recovery phases, may vary based on numerous factors, such as the type of transient grid event, the duration of the transient grid event, wind conditions during the transient grid event and the subsequent recovery phase, etc. Such characteristics of the oscillatory drive train load include the maximum amplitude (e.g., the highest drivetrain load of about 11,500 kNm in the example illustrated at FIG. 6) and the total time to settle (e.g., until the drivetrain load returns to within plus or minus a threshold, such as ten percent or less, of the pre-transient grid event drivetrain load, for example, the pre-transient grid event drivetrain load of about 6,000 kNm in the example illustrated at FIG. 6, or when the drivetrain load returns to a steady state, which may be at or approximately the pretransient grid event drivetrain load). As may be seen in FIG. 6, the drivetrain load in the wind turbine during a recovery phase after a transient grid event, such as the exemplary oscillatory drive train loads 1000 and 1001 illustrated in FIG. 6, undergoes a damped oscillation including several cycles of alternating overshoot (above the pretransient grid event load) and undershoot (below the pre-transient grid event load), where a magnitude or amplitude of each successive cycle is generally less than the immediately preceding cycle.

[0043] Turning now to FIG. 7, exemplary graphs of possible grid power over time during a recovery from a transient grid event are illustrated. In FIG. 7, a first oscillatory grid power 2000 (e.g., during a first recovery phase following a first transient grid event) and a second oscillatory grid power 2002 (e.g., during a second recovery phase following a second transient grid event) are illustrated, as examples of varying oscillatory grid powers during various recovery phases and various possible degrees of damping of the oscillations of the grid power in the various possible recovery phases. In a similar manner as described above with respect to the drivetrain loads illustrated in FIG. 6, the oscillatory grid power may define characteristics such as a maximum amplitude above or below the pre-transient grid event power and the total time to settle (e.g., until the grid power returns to a steady state, which maybe at or approximately the pre-transient grid event grid power). In the examples illustrated in FIG. 7, the pre-transient grid event power is about 5.5 MW or 5500 kW and the maximum amplitude is about 1.2 MW (1200 kW) during the first cycle of the recovery phase for both oscillatory grid powers 2000 and 2002. Also illustrated in FIG. 7 by way of example, the amplitude of the second oscillatory grid power 2002 during the second cycle of the recovery phase is about 700 kW, in both the initial overshoot portion (e.g., about 700 kW above the pre-transient grid event power) and the subsequent undershoot portion (e.g., about 700 kW below the pre-transient grid event power) of the second cycle of the second oscillatory grid power 2002. As may be seen in FIG. 7, the grid power during a recovery phase after a transient grid event, such as one of the exemplary oscillatory grid powers 2000 and 2002 illustrated in FIG. 7, undergoes a damped oscillation including several cycles of alternating overshoot (above the pre-transient grid event power) and undershoot (below the pretransient grid event power), where a magnitude or amplitude of each successive cycle is generally less than the immediately preceding cycle.

[0044] Additionally, those of ordinary skill in the art will recognize that, for a given recovery phase after a transient grid event, the degree of damping in the oscillations of the grid power, e.g., as illustrated at 2000 and/or 2002 in FIG. 7, is generally countervailed by the degree of damping in the oscillations of the drivetrain load, e.g., as illustrated at 1000 and/or 1001 in FIG. 6. For example, there may be a tradeoff between the physical and structural limitations of the wind turbine, e.g., the drivetrain thereof, and the requirements of the electrical grid. Thus, increasing the damping of the oscillations in the drivetrain load to reduce the stress and/or strain on the drivetrain may result in a longer time for the grid power to settle or recover, e.g., return to a steady state such as approximately the pre-transient grid event power level, whereas increasing the damping of the oscillations in the grid power to reduce the time duration of the recovery phase may result in higher physical loads on the wind turbine drivetrain.

[0045] Embodiments of the present subject matter may also include methods for controlling a wind turbine coupled to a power grid, such as wind turbine 100 described above. For example, as noted above, the controller 200 of the wind turbine 100 may be operable to perform some or all steps of such methods. In some embodiments, the controlled wind turbine may include a drivetrain comprising a rotor rotatably coupled to a generator via a slip coupling, e.g., as described above in the context of exemplary wind turbine 100. One example of such methods is illustrated in FIG. 8.

[0046] An exemplary method 800 for controlling a wind turbine coupled to a power grid is illustrated in FIG. 8. As shown at (810), method 800 may include (and controller 200 may be operable for performing) detecting a transient grid event. In some embodiments, the transient grid event may be detected via a controller, such as controller 200. [0047] Method 800 may also include generating one or more torque commands in response to the transient grid event. For example, in some embodiments, the one or more torque commands may be generated by a drive-train-damper control module of the controller, e.g., of controller 200.

[0048] Generating the one or more torque commands may include generating a first torque command (820) and/or a second torque command (822) in response to the transient grid event. For example, the first torque command may be configured to damp a torsional vibration, such as one of the example oscillatory drivetrain loads illustrated in FIG. 6, resulting from the transient grid event. In some embodiments, the second torque command may be configured to minimize an error magnitude of power supplied to the power grid during a recovery phase immediately after the transient grid event. For example, the error may be positive or negative, such as the power supplied to the power grid during the recovery phase may be greater (and thus a positive error) than the pre-transient grid event power or the power supplied to the power grid during the recovery phase may be less (and thus a negative error) than the pre-transient grid event power, while the magnitude of the error is the distance (in either direction, e.g., above or below) by which the power supplied to the power grid during the recovery phase varies from the pre-transient grid event power, e.g., the magnitude of the error may be the absolute value of the error and/or may correspond to an amplitude of the oscillatory power (such as one or both of the oscillatory powers illustrated in FIG. 7, for example).

[0049] In some embodiments, method 800 may further include driving the generator to provide torque based on the one or more torque commands, so as to cause a torsional vibration resulting from the transient grid event to be damped and an error magnitude of power supplied to the power grid during a recovery phase after the transient grid event to be minimized. For example, as illustrated in FIG. 8, method 800 may include (and, as mentioned above and as may be true for any or all of the exemplary method steps described herein, controller 200 may be operable for performing) inputting the first torque command and the second torque command into a timer logic, as shown at (830). Method 800 may then include one or more iterations of each of (840), driving the generator to provide a first torque based on the first torque command for a first time period , and (842), driving the generator to provide a second torque based on the second torque command for a second time period. In some embodiments, the first torque may be less than the second torque. For example, as mentioned above, there may be a trade-off between reducing the structural load on the drivetrain and reducing the length of the recovery phase. Thus, while the lower first torque may be more protective of the drivetrain components, the higher second torque may promote a faster return to equilibrium, e.g., a faster recovery to steadystate power generation.

[0050] In some embodiments, the first time period and the second time period may be determined by the timer logic. For example, determining the first and second time periods by the timer logic may include generating a time pulse based on an estimated drive shaft torque, and a drivetrain load oscillation cycle number may be inferred from the estimated drive shaft torque. Thus, in some embodiments, the first time period and the second time period may each be an integer, e.g., whole number, of cycles of the oscillatory drivetrain load.

[0051] For example, the second time period during which the generator is driven based on the second torque command configured to minimize the error magnitude of power supplied to the power grid may be or include a first cycle of the recovery phase. In such embodiments, initially providing the second torque may prioritize the power recovery, e.g., reducing or minimizing the time duration of the recovery phase. [0052] In some embodiments, the drive-train-damper control module may be operable to generate the first and second torque commands using a closed-loop control algorithm. The closed-loop control algorithm may be, for example, a proportional (P), proportional-integral (PI), or proportional-integral-derivative (PID) feedback-based control algorithm. As will be recognized by those of ordinary skill in the art, closed-loop control algorithms apply one or more gains in arriving at, e.g., generating, an output value. Thus, for example, in some embodiments, generating the first torque command may include applying a first gain in a closed-loop control algorithm, and generating the second torque command may include applying a second gain in the closed-loop control algorithm.

[0053] In some embodiments, the second torque command may be generated based on, e.g., in response to, an error level of power supplied to the power grid greater than a predetermined threshold. For example, the error magnitude may be an input into a closed-loop control algorithm, e.g., such as one of the exemplary algorithms discussed above. For example, the predetermined threshold may be a cutoff threshold wherein the input into the control algorithm that generates the second torque command is the error of the power supplied to the power grid that exceeds the predetermined threshold. As an example of a cut-off threshold, where the predetermined threshold is, e.g., plus or minus ten percent of the pre-transient grid event power, and a power supplied to the power grid is, e.g., fifteen percent greater or less than the pre-transient grid event power, the error magnitude which is input into the control algorithm would be, in this particular example, five percent. In the foregoing example, the exemplary error magnitude of five percent is an example of an error level of power supplied to the power grid greater than a predetermined threshold, e.g., the error level greater than the predetermined threshold is the extent to which the variation in the power presently supplied to the power gride exceeds the predetermined threshold.

[0054] Some such embodiments may include a dynamic threshold, such as a dynamic cut-off threshold. For example, the predetermined threshold may be a first predetermined threshold, and the second torque command may be generated based on the error level of power supplied to the power grid greater than the first predetermined threshold during a first cycle of the recovery phase. In such embodiments, the second torque command may be generated based on the error level of power supplied to the power grid being greater than a second predetermined threshold during a second cycle of the recovery phase after the first cycle of the recovery phase, such as a second cycle immediately after the first cycle or the second cycle may be another subsequent cycle after the first cycle and after at least one cycle of the recovery phase during which the first torque is provided. For example, the dynamic threshold may include diminishing thresholds. Thus, in some embodiments, the second predetermined threshold may be less than the first predetermined threshold. Additional predetermined thresholds may also be included, such as a third predetermined threshold that is less than the second predetermined threshold, etc. For example, the first predetermined threshold may be approximately plus or minus ten percent of the pre-transient grid event power, the second predetermined threshold may be approximately plus or minus eight percent of the pre-transient grid event power, and the third predetermined threshold may be approximately plus or minus six percent of the pre-transient grid event power.

[0055] In some embodiments, exemplary methods for controlling a wind turbine may include a slipping alarm, such as detecting when the drivetrain load is approaching or within a margin, e.g., a tolerance margin or margin of safety, of a decoupling torque of the slip coupling. For example, some embodiments may include monitoring torque in the drivetrain, comparing the torque in the drivetrain to a nominal release threshold of the slip coupling, and driving the generator to provide only the first torque based on the first torque command when the monitored torque is within a predetermined margin of the nominal release threshold of the slip coupling. Thus, the method may prioritize the drivetrain load by providing a torque based on the first torque command that is configured to damp the torsional vibration resulting from the transient grid event whenever a decoupling is imminent or an elevated risk of decoupling is detected, such as in response to a slipping alarm.

[0056] Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0057] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0058] Further aspects of the invention are provided by the subject matter of the following clauses:

[0059] Clause 1. A method for controlling a wind turbine coupled to a power grid, the wind turbine having a drivetrain comprising a rotor rotatably coupled to a generator via a slip coupling, the method comprising: detecting, via a controller, a transient grid event; generating one or more torque commands via a drive-traindamper control module of the controller in response to the transient grid event; and driving the generator to provide torque based on the one or more torque commands, whereby a torsional vibration resulting from the transient grid event is damped and an error magnitude of power supplied to the power grid during a recovery phase after the transient grid event is minimized.

[0060] Clause 2. The method of clause 1, wherein generating one or more torque commands via the drive-train-damper control module of the controller in response to the transient grid event comprises generating a first torque command configured to damp a torsional vibration resulting from the transient grid event and generating a second torque command configured to minimize an error magnitude of power supplied to the power grid during a recovery phase immediately after the transient grid event, wherein driving the generator to provide torque based on the one or more torque commands comprises driving the generator to provide a first torque based on the first torque command for a first time period and driving the generator to provide a second torque based on the second torque command for a second time period, wherein generating the first torque command comprises applying a first gain in a closed-loop control algorithm, and wherein generating the second torque command comprises applying a second gain in the closed-loop control algorithm.

[0061] Clause 3. The method of any preceding clause, wherein the second torque command is generated based on an error level of power supplied to the power grid greater than a predetermined threshold.

[0062] Clause 4. The method of any preceding clause, wherein the predetermined threshold is a first predetermined threshold, wherein the second torque command is generated based on the error level of power supplied to the power grid greater than the first predetermined threshold during a first cycle of the recovery phase, and wherein the second torque command is generated based on the error level of power supplied to the power grid greater than a second predetermined threshold during a second cycle of the recovery phase after the first cycle of the recovery phase. [0063] Clause 5. The method of any preceding clause, wherein the second predetermined threshold is less than the first predetermined threshold.

[0064] Clause 6. The method of any preceding clause, further comprising generating the second torque command based on the error level of power supplied to the power grid greater than a third predetermined threshold during a third cycle of the recovery phase after the second cycle of recovery phase.

[0065] Clause 7. The method of any preceding clause, wherein the second predetermined threshold is less than the first predetermined threshold and the third predetermined threshold is less than the second predetermined threshold.

[0066] Clause 8. The method of any preceding clause, wherein the first time period and the second time period are determined based on a timer logic.

[0067] Clause 9. The method of any preceding clause, wherein the timer logic generates a time pulse based on an estimated torque in the drivetrain, and wherein the time pulse corresponds to a cycle of a drivetrain load oscillation.

[0068] Clause 10. The method of any preceding clause, further comprising monitoring torque in the drivetrain, comparing the torque in the drivetrain to a nominal release threshold of the slip coupling, and driving the generator to provide only the first torque based on the first torque command when the monitored torque is within a predetermined margin of the nominal release threshold of the slip coupling. [0069] Clause 11. A system for controlling a wind turbine, the system comprising: a drivetrain comprising a generator rotatably coupled to a rotor via a slip coupling; and a controller communicatively coupled to the generator, the controller comprising at least one processor configured to perform a plurality of operations, the plurality of operations comprising: detecting a transient grid event, generating one or more torque commands via a drive-train-damper control module of the controller in response to the transient grid event; and driving the generator to provide torque based on the one or more torque commands, whereby a torsional vibration resulting from the transient grid event is damped and an error magnitude of power supplied to the power grid during a recovery phase after the transient grid event is minimized.

[0070] Clause 12. The system of clause 11, wherein generating one or more torque commands via the drive-train-damper control module of the controller in response to the transient grid event comprises generating a first torque command configured to damp a torsional vibration resulting from the transient grid event and a second torque command configured to minimize an error magnitude of power supplied to the power grid during a recovery phase immediately after the transient grid event, wherein driving the generator to provide torque based on the one or more torque commands comprises driving the generator to provide a first torque based on the first torque command for a first time period and driving the generator to provide a second torque based on the second torque command for a second time period, wherein generating the first torque command comprises applying a first gain in a closed-loop control algorithm, and wherein generating the second torque command comprises applying a second gain in the closed-loop control algorithm.

[0071] Clause 13. The system of any preceding clause, wherein the second torque command is generated based on an error level of power supplied to the power grid greater than a predetermined threshold.

[0072] Clause 14. The system of any preceding clause, wherein the predetermined threshold is a first predetermined threshold, wherein the second torque command is generated based on the error level of power supplied to the power grid greater than the first predetermined threshold during a first cycle of the recovery phase, and wherein the second torque command is generated based on the error level of power supplied to the power grid greater than a second predetermined threshold during a second cycle of the recovery phase after the first cycle of the recovery phase. [0073] Clause 15. The system of any preceding clause, wherein the second predetermined threshold is less than the first predetermined threshold.

[0074] Clause 16. The system of any preceding clause, further comprising generating the second torque command based on the error level of power supplied to the power grid greater than a third predetermined threshold during a third cycle of the recovery phase after the second cycle of recovery phase. [0075] Clause 17. The system of any preceding clause, wherein the second predetermined threshold is less than the first predetermined threshold and the third predetermined threshold is less than the second predetermined threshold.

[0076] Clause 18. The system of any preceding clause, wherein the first time period and the second time period are determined based on a timer logic.

[0077] Clause 19. The system of any preceding clause, wherein the timer logic generates a time pulse based on an estimated torque in the drivetrain, and wherein the time pulse corresponds to a cycle of a drivetrain load oscillation.

[0078] Clause 20. The system of any preceding clause, wherein the plurality of operations further comprises monitoring torque in the drivetrain, comparing the torque in the drivetrain to a nominal release threshold of the slip coupling, and driving the generator to provide only the first torque based on the first torque command when the monitored torque is within a predetermined margin of the nominal release threshold of the slip coupling.

Claims

WHAT IS CLAIMED IS:

1. A method for controlling a wind turbine coupled to a power grid, the wind turbine having a drivetrain comprising a rotor rotatably coupled to a generator via a slip coupling, the method comprising: detecting, via a controller, a transient grid event; generating one or more torque commands via a drive-train-damper control module of the controller in response to the transient grid event; and driving the generator to provide torque based on the one or more torque commands, whereby a torsional vibration resulting from the transient grid event is damped and an error magnitude of power supplied to the power grid during a recovery phase after the transient grid event is minimized.

2. The method of claim 1, wherein generating one or more torque commands via the drive-train-damper control module of the controller in response to the transient grid event comprises generating a first torque command configured to damp a torsional vibration resulting from the transient grid event and generating a second torque command configured to minimize an error magnitude of power supplied to the power grid during a recovery phase immediately after the transient grid event, wherein driving the generator to provide torque based on the one or more torque commands comprises driving the generator to provide a first torque based on the first torque command for a first time period and driving the generator to provide a second torque based on the second torque command for a second time period, wherein generating the first torque command comprises applying a first gain in a closed-loop control algorithm, and wherein generating the second torque command comprises applying a second gain in the closed-loop control algorithm.

3. The method of claim 2, wherein the second torque command is generated based on an error level of power supplied to the power grid greater than a predetermined threshold.

4. The method of claim 3, wherein the predetermined threshold is a first predetermined threshold, wherein the second torque command is generated based on the error level of power supplied to the power grid greater than the first predetermined threshold during a first cycle of the recovery phase, and wherein the second torque command is generated based on the error level of power supplied to the power grid greater than a second predetermined threshold during a second cycle of the recovery phase after the first cycle of the recovery phase.

5. The method of claim 4, wherein the second predetermined threshold is less than the first predetermined threshold.

6. The method of claim 4, further comprising generating the second torque command based on the error level of power supplied to the power grid greater than a third predetermined threshold during a third cycle of the recovery phase after the second cycle of recovery phase.

7. The method of claim 6, wherein the second predetermined threshold is less than the first predetermined threshold and the third predetermined threshold is less than the second predetermined threshold.

8. The method of claim 2, wherein the first time period and the second time period are determined based on a timer logic.

9. The method of claim 8, wherein the timer logic generates a time pulse based on an estimated torque in the drivetrain, and wherein the time pulse corresponds to a cycle of a drivetrain load oscillation.

10. The method of claim 2, further comprising monitoring torque in the drivetrain, comparing the torque in the drivetrain to a nominal release threshold of the slip coupling, and driving the generator to provide only the first torque based on the first torque command when the monitored torque is within a predetermined margin of the nominal release threshold of the slip coupling.

11. A system for controlling a wind turbine, the system comprising: a drivetrain comprising a generator rotatably coupled to a rotor via a slip coupling; and a controller communicatively coupled to the generator, the controller comprising at least one processor configured to perform a plurality of operations, the plurality of operations comprising: detecting a transient grid event; generating one or more torque commands via a drive-train-damper control module of the controller in response to the transient grid event; and driving the generator to provide torque based on the one or more torque commands, whereby a torsional vibration resulting from the transient grid event is damped and an error magnitude of power supplied to the power grid during a recovery phase after the transient grid event is minimized.

12. The system of claim 11, wherein generating one or more torque commands via the drive-train-damper control module of the controller in response to the transient grid event comprises generating a first torque command configured to damp a torsional vibration resulting from the transient grid event and a second torque command configured to minimize an error magnitude of power supplied to the power grid during a recovery phase immediately after the transient grid event, wherein driving the generator to provide torque based on the one or more torque commands comprises driving the generator to provide a first torque based on the first torque command for a first time period and driving the generator to provide a second torque based on the second torque command for a second time period, wherein generating the first torque command comprises applying a first gain in a closed-loop control algorithm, and wherein generating the second torque command comprises applying a second gain in the closed-loop control algorithm.

13. The system of claim 12, wherein the second torque command is generated based on an error level of power supplied to the power grid greater than a predetermined threshold.

14. The system of claim 13, wherein the predetermined threshold is a first predetermined threshold, wherein the second torque command is generated based on the error level of power supplied to the power grid greater than the first predetermined threshold during a first cycle of the recovery phase, and wherein the second torque command is generated based on the error level of power supplied to the power grid greater than a second predetermined threshold during a second cycle of the recovery phase after the first cycle of the recovery phase.

15. The system of claim 14, wherein the second predetermined threshold is less than the first predetermined threshold.

16. The system of claim 14, further comprising generating the second torque command based on the error level of power supplied to the power grid greater than a third predetermined threshold during a third cycle of the recovery phase after the second cycle of recovery phase.

17. The system of claim 16, wherein the second predetermined threshold is less than the first predetermined threshold and the third predetermined threshold is less than the second predetermined threshold.

18. The system of claim 12, wherein the first time period and the second time period are determined based on a timer logic.

19. The system of claim 18, wherein the timer logic generates a time pulse based on an estimated torque in the drivetrain, and wherein the time pulse corresponds to a cycle of a drivetrain load oscillation.

20. The system of claim 12, wherein the plurality of operations further comprises monitoring torque in the drivetrain, comparing the torque in the drivetrain to a nominal release threshold of the slip coupling, and driving the generator to provide only the first torque based on the first torque command when the monitored torque is within a predetermined margin of the nominal release threshold of the slip coupling.