System and method for controlling a wind turbine

Abstract

A system and method for controlling a wind turbine is provided. A controller of a wind turbine detects a transient grid event and generates a first torque command via a driveline damper control module. The first torque command is configured to damp torsional vibrations caused by a transient grid event. The controller also generates a second torque command via a driveline 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 for a first period of time based on the first torque command and to provide a second torque for a second period of time based on the second torque command.

Description

Technical Field

[0001] The present disclosure generally relates to wind turbines, and more particularly to systems and methods for controlling a wind turbine in response to transient grid events. Background Art

[0002] Wind power is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines have received increased attention in this regard. Modern wind turbines typically include 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 coupled to the generator. The rotor assembly and the gearbox are mounted on a platen support frame located within the nacelle. One or more rotor blades capture the kinetic energy of the wind using known airfoil principles. The rotor blades transfer the kinetic energy in the form of rotational energy to rotate a shaft that couples the rotor blades to the gearbox, or, if no gearbox is used, the shaft couples the rotor blades directly to the generator. The generator then converts the mechanical energy into electrical energy, and the electrical energy can be transmitted to a converter and / or transformer housed within the tower and subsequently deployed to the utility grid. Modern wind power generation systems typically take the form of a wind farm having a plurality of such wind turbine generators that are operable to supply power to a transmission system that provides power to the power grid.

[0003] In order to supply power to the power grid, wind turbines generally need to meet certain grid requirements. For example, a wind turbine may be required to provide fault ride-through (e.g., low voltage ride-through) capability. This requirement may mandate that the wind turbine remain 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 terms are intended to encompass a change in the magnitude of the grid voltage over a certain duration. For example, when a grid fault occurs, the voltage of the system can decrease by a significant portion within a short duration (e.g., typically less than 500 milliseconds). Additionally, grid faults can occur for a variety of reasons, including but not limited to a phase conductor connected to ground (i.e., a ground fault), a short circuit between phase conductors, lightning and / or storms, and / or an accidental transmission line grounding.

[0004] In the past, a wind turbine could be immediately disconnected in response to a voltage drop. However, as the power output of the wind turbine increases as a percentage of the power of the power grid, there is an increasing desire for the wind turbine to remain online and ride through transient grid events. However, the voltage drop during a transient grid event can cause a significant reduction in the torque of the generator, while the rotational speed of the rotor can remain substantially unchanged. Accordingly, when the voltage returns to the pre-fault level, the mismatch between the torque of the generator and the inertia of the rotor can cause undesirable torsional vibrations in the drivetrain of the wind turbine. Torsional vibrations can have a negative impact on the life cycle of various components of the wind turbine and / or can manifest as oscillations in the power generated by the wind turbine that exceed certain power grid limits. For example, the torsional vibrations can exceed the release threshold of a slip coupling, causing the rotor to become operably disengaged from the generator.

[0005] Accordingly, there is a continuing search in the art for new and improved systems and methods to address the aforementioned problems. Accordingly, the present disclosure is directed to systems and methods for controlling a wind turbine in response to a transient grid event to manage torsional vibrations caused by the transient grid event and oscillations in the power output of the wind turbine. Summary of the Invention

[0006] Aspects and advantages of the invention will be set forth in part in the description which follows, or may be obvious from the description, or may be learned by 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 that includes a rotor rotatably coupled to a generator via a slip coupling. The method may include detecting a transient grid event via a controller. Additionally, the method may include generating, in response to the transient grid event, one or more torque commands via a drivetrain damper control module of the controller. Further, the method may include driving the generator based on the one or more torque commands to provide torque. As a result of driving the generator based on the one or more torque commands to provide torque, torsional vibrations caused by the transient grid event are damped, and the error magnitude of the 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 complete and enabling disclosure of the present invention, including the best mode thereof, for one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which:

[0011] Figure 1 FIG. illustrates a perspective view of an embodiment of a wind turbine in accordance with the present disclosure;

[0012] Figure 2 FIG. illustrates an interior perspective view of an embodiment of a nacelle of a wind turbine in accordance with the present disclosure;

[0013] Figure 3 FIG. illustrates a schematic view of an embodiment of a drivetrain of a wind turbine in accordance with the present disclosure;

[0014] Figure 4 FIG. illustrates a schematic view of an embodiment of an electrical system for use with a wind turbine in accordance with the present disclosure;

[0015] Figure 5 FIG. illustrates a block diagram of an embodiment of a controller for use with a wind turbine in accordance with the present disclosure;

[0016] Figure 6 FIG. illustrates a graphical representation of damped torsional vibrations in accordance with the present disclosure;

[0017] Figure 7 FIG. illustrates a graphical representation of damped power oscillations in accordance with the present disclosure; and

[0018] Figure 8 FIG. illustrates a flowchart diagram of an embodiment of a method for controlling a wind turbine in accordance with the present disclosure.

[0019] The repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the invention. DETAILED DESCRIPTION

[0020] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the present invention and not limitation thereof. 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 thereof. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still another embodiment. Accordingly, it is intended that the present invention cover 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 component or step, and are not intended to denote the position or importance of individual components or the order of individual steps.

[0022] The terms "coupled", "fixed", "attached to", etc. refer to both direct coupling, fixing, or attaching and indirect coupling, fixing, or attaching through one or more intermediate components or features, unless specifically stated otherwise herein.

[0023] As used throughout the specification and claims herein, approximate language is applied to modify any quantitative representation that admits of variation without resulting in a change in the basic function associated therewith. Thus, a value modified by one or more terms such as "about", "approximately", "substantially", and "essentially" will not be limited to the precise value specified. In at least some instances, the approximate language may correspond to the precision of the instrument used to measure the value, or the precision of the method or machine used to construct or manufacture the component and / or system. For example, the approximate language may refer to within a margin of 10%.

[0024] Here and throughout the specification and claims, ranges are combined and interchanged, such ranges are identified and include all the subranges subsumed therein, unless the context or language indicates otherwise. For example, all ranges disclosed herein include the endpoints, and the endpoints can be combined independently of each other.

[0025] Generally, the present disclosure is directed to systems and methods for controlling a wind turbine to increase the effectiveness of a drive train damper (DTD) control system with respect to both damping torsional vibrations caused by transient grid events and reducing oscillations in the electrical power delivered by the wind turbine to the power grid after a 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 grid event and continues until grid power stabilizes). Typically, a wind turbine utilizes torque generated by a generator to counteract torque generated by a rotor in response to wind. Many modern wind turbines employ generators, such as doubly-fed induction generators (DFIGs), which utilize grid power for generating generator torque. At the onset of a transient grid event (such as a low voltage ride through (LVRT) event), grid power can suddenly decrease, resulting in a corresponding decrease in generator torque. However, due to inertia and / or the influence of wind, the rotor can continue to rotate at the same speed, and in some instances, when the rotation is not significantly impeded by generator torque, the rotor can accelerate. When the transient grid event ends and grid power returns, the generator can quickly resume generating generator torque to return the wind turbine to a power generation state. However, within the drive train of the wind turbine, the generator torque can meet the torque caused by the rotation of the rotor. This meeting can generate torsional vibrations within the drive train. A DTD control system can be employed to quickly damp the resulting torsional vibrations. However, such quick damping can also result in a longer recovery period after a transient grid event and greater oscillations in grid power during the recovery period. The present disclosure can vary the damping level applied to the torsional vibrations over time throughout the recovery period to balance a reduction in structural loads on the drive train and a reduction in the oscillatory nature of power recovery. Thus, the systems and methods of the present disclosure can increase the effectiveness of the DTD control system.

[0026] Referring now to the drawings, Figure 1 FIG. 5 illustrates a perspective view of one embodiment of a wind turbine 100 in accordance with 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 alternative embodiments, the rotor 108 can include more or fewer than three rotor blades 112. Each rotor blade 112 can be spaced about the hub 110 to facilitate rotation of the rotor 108 such that kinetic energy can be converted from wind into useful mechanical energy and subsequently into electrical energy. For example, the hub 110 can be rotatably coupled to a generator 118 of an electrical system 150 ( Figure 2 ) located within the nacelle 106 ( Figure 2) to allow the generation of electrical energy.

[0027] The wind turbine 100 may also include a controller 200 concentrated 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 external to the wind turbine. Additionally, the controller 200 may be communicatively coupled to any number of components of the wind turbine 100 in order to control those components. Accordingly, 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 that cause the controller 200 to perform or implement operations (such as one or more method steps, such as the steps of the exemplary methods described herein). Thus, it should be noted that the controller 200, as disclosed herein, is capable and may be capable of operating to perform any method and associated method steps as disclosed herein.

[0028] Now refer to Figures 2 to 4 , a simplified internal view of one embodiment of the nacelle 106, a schematic diagram of one embodiment of the drivetrain 146, and Figure 1 the exemplary electrical system 150 of the wind turbine 100 shown in

[0029] In an embodiment, the rotor 108 may be slowed via the torque generated by the generator 118. Since the generator 118 may generate a torque opposite 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 the components of the drive train 146 due to an overload of the drive train 146. Accordingly, the slip coupling 154 may have a release threshold or traction force above which the slip coupling 154 may allow the first portion 162 and the second portion 164 of the high-speed shaft 124 to have different rotational speeds. It should be appreciated that if the torsional moment at the slip coupling 154 exceeds the release / traction force threshold, the generator 118 may be communicatively disengaged from the rotor 108. In such a case, the torque generated by the generator 118 may not be available to slow the rotor 108, or the increased rotational speed of the rotor 108 may not be available 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 an embodiment, the pitch drive motor 128 may be coupled to the pitch drive gearbox 130 such that the pitch drive motor 128 applies a 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 the corresponding rotor blade 112 such that rotation of the pitch drive pinion 132 causes rotation of the pitch bearing 134. Thus, in such an embodiment, 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 (one or more) rotor blades 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, where each yaw drive mechanism 138 is configured to change the angle of the nacelle 106 relative to the wind (e.g., by engaging the yaw bearing 140 of the wind turbine 100).

[0031] Specifically referring to Figure 2, in an embodiment, the wind turbine 100 may include at least one operating sensor 158. The operating sensor(s) 158 may be configured to detect the performance of the wind turbine 100, e.g., in response to environmental conditions. For example, the operating sensor(s) 158 may be a rotational speed sensor operably coupled to the controller 200. The operating sensor(s) 158 may be directed at the rotor shaft 122 and / or the generator 118 of the wind turbine 100. The operating sensor(s) 158 may collect data indicative of the rotational speed and / or rotational position of the rotor shaft 122 and thus the rotor 108 in the form of rotor speed and / or rotor azimuth angle. In an embodiment, the operating sensor(s) 158 may be an analog tachometer, a DC tachometer, an AC tachometer, a digital tachometer, a contact tachometer, a non-contact tachometer, or a time and frequency tachometer. In an embodiment, the operating sensor(s) 158 may be, for example, an encoder, such as an optical encoder. In an embodiment, the operating sensor(s) 158 may be configured to monitor the operating parameters 338 of the wind turbine 100. For example, the operating 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 the three phases of power.

[0032] In addition, 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. Thus, in an embodiment, the grid sensor(s) 160 may 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 its variants indicate that the various sensors of the wind turbine 100 may be configured to provide either a direct measurement of the monitored parameter or an indirect measurement of such a parameter. Thus, the sensors described herein may be used, for example, to generate signals related to the monitored parameter, which signals may then be utilized by the controller 200 to determine the condition or response of the wind turbine 100.

[0034] With particular reference to Figure 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 the 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 the stator bus 166 and the power converter 168 via the rotor bus 170. In such a configuration, the stator bus 166 may provide an output polyphase power (e.g., three-phase power) from the stator of the generator 118, and the rotor bus 170 may provide an output polyphase power (e.g., three-phase power) of the generator rotor 119 of the generator 118. Additionally, the generator 118 may be coupled to the rotor-side converter 172 via the rotor bus 170. The rotor-side converter 172 may be coupled to the line-side converter 174, which in turn may be coupled to the line-side bus 176.

[0035] In an embodiment, the rotor-side converter 172 and the line-side converter 174 may be configured for a normal operating mode in a three-phase pulse width modulation (PWM) arrangement that uses insulated gate bipolar transistors (IGBTs) as switching devices. Other suitable switching devices may be used, such as insulated gate commutated thyristors, MOSFETs, bipolar transistors, silicon controlled rectifiers, 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, and a DC link capacitor 175 may be across the DC link 173.

[0036] In an embodiment, the power converter 168 may be coupled to a 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 the switching elements used in the power converter 168 to establish a desired generator torque set point and / or power output.

[0037] As Figure 4Further depicted in the embodiments, the electrical system 150 may include a transformer 178 that couples the wind turbine 100 to the power grid 179. In an embodiment, the transformer 178 may be a three-winding transformer that 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 may be a three-winding transformer as depicted, or alternatively, may be a two-winding transformer having only the primary winding 180 and the secondary winding 182; may be a four-winding transformer having the primary winding 180, the secondary winding 182, the auxiliary winding 184, and additional auxiliary windings; 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, in an embodiment, the electrical system 150 may include a grid circuit breaker 188, a stator bus circuit breaker 190, and / or a line bus circuit breaker 192. When the conditions of the electrical system 150 approach the operating thresholds of the electrical system 150, the (multiple) circuit breakers 188, 190, 192 of the electrical system 150 may connect or disconnect the corresponding components of the electrical system 150.

[0039] Still referring to Figure 4 And also referring to Figure 5 , an embodiment of a system 300 for controlling a wind turbine 100 according to the present disclosure is presented. As Figure 5Specifically shown therein, the illustration may include a schematic diagram of one embodiment of suitable components within system 300. For example, as shown, system 300 may include a controller 200 communicatively coupled to (one or more) operation sensors 158 and (one or more) grid sensors 160. Additionally, as shown, controller 200 includes one or more processors 206 and associated memory devices 208, which are configured to perform various computer-implemented functions (e.g., execute methods, steps, calculations, etc. and store related data, as disclosed herein). Further, controller 200 may also include a communication module 210 to facilitate communication between controller 200 and various components of wind turbine 100. Additionally, communication module 210 may include a sensor interface 212 (e.g., one or more analog-to-digital converters) to allow signals transmitted from (one or more) sensors 158, 160 to be converted into signals understandable and processable by processor 206. It should be appreciated that (one or more) sensors 158, 160 may be communicatively coupled to communication module 210 using any suitable means. For example, (one or more) sensors 158, 160 may be coupled to sensor interface 212 via a wired connection. However, in other embodiments, (one or more) sensors 158, 160 may be coupled to sensor interface 212 via a wireless connection, such as by using any suitable wireless communication protocol known in the art. Additionally, communication module 210 may also be operatively coupled to an operation state control module 214, which is configured to change at least one wind turbine operation state. Controller 200 may further include a drivetrain damper control module 216, such that, for example, controller 200 may generate torque commands via drivetrain damper control module 216 in response to transient grid events.

[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 to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Additionally, (one or more) memory devices 208 may generally include (one or more) memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk-read only memory (CD-ROM), magneto-optical disk (MOD), digital versatile disk (DVD), and / or other suitable memory elements. (One or more) such memory devices 208 may generally be configured to store suitable computer-readable instructions, which when implemented by (one or more) processors 206 configure controller 200 to perform various functions, including but not limited to any of the exemplary methods and method steps described herein, as well as various other suitable computer-implemented functions.

[0041] Figure 6and Figure 7 Illustrates exemplary oscillations through the recovery period or recovery phase of a wind turbine following a transient grid event (such as a low voltage fault, etc.). The numerical values are provided by way of illustration only in Figure 6 and Figure 7 to inform the examples depicted therein, and such quantities are in no way intended to limit the subject matter in any respect.

[0042] Now specifically referring to Figure 6 , an exemplary graph is illustrated showing the possible drivetrain load in a wind turbine drivetrain varying over time during recovery from a transient grid event (e.g., during the recovery phase immediately following the transient grid event). In Figure 6 , the first oscillating drivetrain load 1000 (e.g., during the first recovery phase after the first transient grid event) and the second oscillating drivetrain load 1001 (e.g., during the second recovery phase after the second transient grid event) are illustrated as examples of the varying oscillating drivetrain load in various recovery phases and the various possible damping levels of the oscillation of the drivetrain load in various possible recovery phases. The characteristics of the oscillating drivetrain load in each recovery phase (e.g., the first oscillating drivetrain load 1000, the second oscillating drivetrain load 1001, and / or other possible oscillating drivetrain loads in other possible recovery phases) can vary based on many factors such as: the type of transient grid event, the duration of the transient grid event, the wind conditions during the transient grid event and the subsequent recovery phase, etc. Such characteristics of the oscillating drivetrain load include the maximum amplitude (e.g., in the example illustrated at Figure 6 , a highest drivetrain load of approximately 11500 kNm) and the total time to settle (e.g., until the drivetrain load returns within a positive or negative threshold (such as 10% or less) of the pre-transient grid event drivetrain load, e.g., in the example illustrated at Figure 6 , a pre-transient grid event drivetrain load of approximately 6000 kNm, or when the drivetrain load returns to a steady state, which steady state can be at or approximately the pre-transient grid event drivetrain load). As can be seen in Figure 6 , the drivetrain load in a wind turbine during the recovery phase after a transient grid event (such as the exemplary oscillating drivetrain loads 1000 and 1001 illustrated in Figure 6 ) undergoes damped oscillations, which include several cycles of alternating overshoots (above the pre-transient grid event load) and undershoots (below the pre-transient grid event load), where the magnitude or amplitude of each successive cycle is generally less than the immediately preceding cycle.

[0043] Now turning to Figure 7 , an exemplary graph is illustrated showing the possible grid power varying over time during recovery from a transient grid event. InFigure 7 illustrates a first oscillating grid power 2000 (e.g., during a first recovery phase after a first transient grid event) and a second oscillating grid power 2002 (e.g., during a second recovery phase after a second transient grid event) as examples of the varying oscillating grid power during various recovery phases and the various possible damping degrees of the oscillation of the grid power in various possible recovery phases. In a manner similar to that described above with respect to Figure 6 the driveline load illustrated in, the oscillating grid power can define characteristics such as a maximum magnitude above or below the pre-transient grid event power and a total time to settle (e.g., until the grid power returns to a steady state, which can be at or approximate to the pre-transient grid event grid power). In the Figure 7 example illustrated in, for both the oscillating grid powers 2000 and 2002, the pre-transient grid event power is approximately 5.5 MW or 5500 kW, and during the first cycle of the recovery phase, the maximum magnitude is approximately 1.2 MW (1200 kW). Figure 7 also illustrated by way of example in, in both the initial overshoot portion (e.g., approximately 700 kW above the pre-transient grid event power) and the subsequent undershoot portion (e.g., approximately 700 kW below the pre-transient grid event power) of the second cycle of the second oscillating grid power 2002, the magnitude of the second oscillating grid power 2002 during the second cycle of the recovery phase is approximately 700 kW. As Figure 7 can be seen in, the grid power (such as Figure 7 one of the exemplary oscillating grid powers 2000 and 2002 illustrated in) during the recovery phase after a transient grid event undergoes damped oscillations that include a number of cycles of alternating overshoots (above the pre-transient grid event power) and undershoots (below the pre-transient grid event power), where the 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 oscillation of the grid power (e.g., as illustrated at 2000 and / or 2002 in Figure 7 ) is generally determined by the degree of damping in the oscillation of the driveline load (e.g., as illustrated in Figure 6Cancellation (illustrated at 1000 and / or 1001 in). For example, there may be a trade-off between the physical and structural limitations of a wind turbine (such as its drivetrain) and the requirements of the power grid. Thus, increasing the damping of the oscillations of the drivetrain load to reduce stress and / or strain on the drivetrain may result in a longer time for the grid power to stabilize or recover (e.g., return to a steady state, such as approximately the power level before a transient grid event), while increasing the damping of the oscillations of the grid power to reduce the 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 the 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 of the steps of such a method. In some embodiments, the controlled wind turbine may include a drivetrain that includes a rotor rotatably coupled to a generator via a slip coupling, such as described above in the context of the exemplary wind turbine 100. Figure 8 An example of such a method is illustrated in.

[0046] Figure 8 An exemplary method 800 for controlling a wind turbine coupled to a power grid is illustrated in. As shown at (810), the method 800 may include (and the controller 200 may be operable to perform) detecting a transient grid event. In some embodiments, the transient grid event may be detected via a controller (such as the controller 200).

[0047] The 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 drivetrain damper control module of the controller (e.g., the controller 200).

[0048] Generating 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 torsional vibrations caused by the transient grid event, such as Figure 6One of the exemplary oscillatory drive train loads illustrated therein. In some embodiments, the second torque command may be configured to minimize the amount of error in the power supplied to the power grid during a recovery phase immediately following a transient grid event. For example, the error may be positive or negative, such that the power supplied to the power grid during the recovery phase may be greater than (and thus a positive error) the power before the transient grid event, or the power supplied to the power grid during the recovery phase may be less than (and thus a negative error) the power before the transient grid event, and the amount of error is the distance by which the power supplied to the power grid during the recovery phase varies from the power before the transient grid event (in either direction, e.g., above or below), e.g., the amount of error may be the absolute value of the error and / or may correspond to the magnitude of oscillatory power (such as, for example Figure 7 one or both of the oscillatory powers illustrated therein).

[0049] In some embodiments, method 800 may further include driving the generator based on one or more torque commands to provide torque so as to damp torsional vibrations caused by a transient grid event and to minimize the amount of error in the power supplied to the power grid during a recovery phase after the transient grid event. For example, as Figure 8 illustrated therein, method 800 may include (and as mentioned above, and as may be the case for any or all of the exemplary method steps described herein, controller 200 may be operable to perform) inputting a first torque command and a second torque command into timer logic, as shown at (830). Then, method 800 may include one or more iterations of each of the following steps: (840), driving the generator based on the first torque command to provide a first torque for a first time period; and (842), driving the generator based on the second torque command to provide a second torque 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 drive train and reducing the length of the recovery phase. Thus, while a lower first torque may protect the drive train components more, a higher second torque may facilitate a faster return to equilibrium, e.g., a faster recovery to steady-state 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 time period and the second time period by the timer logic may include generating time pulses based on an estimated drive shaft torque and inferring the number of drive train load oscillation cycles from the estimated drive shaft torque. Thus, in some embodiments, the first time period and the second time period may each be an integer number of cycles of the oscillatory drive train load, e.g., a whole number.

[0051] For example, a second time period during which the generator is driven based on a second torque command configured to minimize the amount of error in the power supplied to the power grid may be or include a first cycle of a recovery phase. In such an embodiment, initially providing the second torque may prioritize power recovery, e.g., reducing or minimizing the duration of the recovery phase.

[0052] In some embodiments, the driveline damper control module may be operable to generate a first torque command and a second torque command using a closed-loop control algorithm. The closed-loop control algorithm may be, for example, a control algorithm based on proportional (P), proportional-integral (PI), or proportional-integral-derivative (PID) feedback. As will be recognized by those of ordinary skill in the art, a closed-loop control algorithm applies one or more gains when obtaining (e.g., generating) an output value. Thus, for example, in some embodiments, generating the first torque command may include applying a first gain in the 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 in the power supplied to the power grid that is greater than a predetermined threshold. For example, the amount of error may be an input to the closed-loop control algorithm (e.g., one of the exemplary algorithms discussed above). For example, the predetermined threshold may be a cut-off threshold, where the input to the control algorithm for generating the second torque command is the error in 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, for example, plus or minus 10% of the pre-transient grid event power, and the power supplied to the power grid is, for example, 15% greater or less than the pre-transient grid event power, the amount of error input to the control algorithm in this particular example would be 5%. In the foregoing example, the exemplary 5% amount of error is an example of an error level in the power supplied to the power grid that is greater than the predetermined threshold, e.g., the error level greater than the predetermined threshold is the extent to which the current power supplied to the power grid varies beyond the predetermined threshold.

[0054] Some such embodiments may include dynamic thresholds, such as a dynamic cut-off threshold. For example, a predetermined threshold may be a first predetermined threshold, and a second torque command may be generated based on an error level greater than the first predetermined threshold of the power supplied to the power grid during a first period of a recovery phase. In such an embodiment, the second torque command may be generated based on an error level of the power supplied to the power grid during a second period (such as a second period immediately following the first period of the recovery phase, or the second period may be another subsequent period after the first period and after at least one period of the recovery phase during which a first torque is provided) after the first period of the recovery phase being greater than a second predetermined threshold. For example, the dynamic threshold may include a decreasing threshold. 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 less than the second predetermined threshold, and so on. For example, the first predetermined threshold may be approximately plus or minus 10% of the power before a transient grid event, the second predetermined threshold may be approximately plus or minus 8% of the power before a transient grid event, and the third predetermined threshold may be approximately plus or minus 6% of the power before a transient grid event.

[0055] In some embodiments, an exemplary method for controlling a wind turbine may include a slip alert, such as detecting when a driveline load approaches or is within a margin (e.g., a tolerance margin or a safety margin) of the disengagement torque of a slip coupling. For example, some embodiments may include monitoring the torque in the driveline, comparing the torque in the driveline to a nominal release threshold of the slip coupling, and driving a generator to provide only a first torque based on a 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 driveline load by providing torque based on a first torque command configured to damp torsional vibrations caused by a transient grid event whenever disengagement is about to occur or a heightened risk of disengagement is detected (such as in response to a slip alert).

[0056] Furthermore, those skilled in the art 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 method and feature, may be mixed and matched by those of ordinary skill in the art to construct additional systems and techniques in accordance with the principles of the present disclosure. Of course, it will be understood that not necessarily all such objectives or advantages described above may be achieved in any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or performed in a manner that achieves or optimizes one advantage or a group of advantages as taught herein, without necessarily achieving other objectives 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 enables any person skilled in the art to practice the invention (including making and using any device or system, and performing any incorporated method). The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. If such other examples include structural elements that are not different from the literal language of the claims, or if such other examples include equivalent structural elements that have no substantial difference from the literal language of the claims, then such other examples are intended to be within the scope of the claims.

[0058] Additional 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 drive train that includes a rotor rotatably coupled to a generator via a slip coupling, the method comprising: detecting a transient grid event via a controller; generating, in response to the transient grid event, one or more torque commands via a drive train damper control module of the controller; and driving the generator based on the one or more torque commands to provide torque, whereby torsional vibrations caused by the transient grid event are damped and the error magnitude of the power supplied to the power grid during a recovery phase after the transient grid event is minimized.

[0060] Clause 2. The method according to 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 includes: generating a first torque command configured to damp torsional vibrations caused by the transient grid event; and generating a second torque command configured to minimize the error magnitude of the power supplied to the power grid during a recovery phase immediately following the transient grid event, wherein driving the generator based on the one or more torque commands to provide torque includes: driving the generator based on the first torque command to provide a first torque for a first time period; and driving the generator based on the second torque command to provide a second torque for a second time period, wherein generating the first torque command includes applying a first gain in a closed-loop control algorithm, and wherein generating the second torque command includes applying a second gain in a closed-loop control algorithm.

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

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

[0063] Clause 5. A method according to any of the preceding clauses, wherein the second predetermined threshold is less than the first predetermined threshold.

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

[0065] Clause 7. A method according to any of the preceding clauses, 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. A method according to any of the preceding clauses, wherein the first time period and the second time period are determined based on timer logic.

[0067] Clause 9. A method according to any of the preceding clauses, wherein the timer logic generates time pulses based on an estimated torque in the drive train, and wherein the time pulses correspond to the periods of the drive train load oscillations.

[0068] Clause 10. A method according to any of the preceding clauses, further comprising: monitoring the torque in the drive train, comparing the torque in the drive train with a nominal release threshold of the slip coupling, and when the monitored torque is within a predetermined margin of the nominal release threshold of the slip coupling, driving the generator based on the first torque command to provide only the first torque.

[0069] Clause 11. A system for controlling a wind turbine, the system comprising: a drive train including a generator rotatably coupled to a rotor via a slip coupling; and a controller communicatively coupled to the generator, the controller including at least one processor configured to perform a plurality of operations, the plurality of operations including: detecting a transient grid event; generating, in response to the transient grid event, one or more torque commands via a drive train damper control module of the controller; and driving the generator based on the one or more torque commands to provide torque, whereby torsional vibrations caused by the transient grid event are damped and the error magnitude of the power supplied to the power grid during a recovery phase after the transient grid event is minimized.

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

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

[0072] Clause 14. The system according to any of the preceding clauses, wherein the predetermined threshold is a first predetermined threshold, wherein the second torque command is generated based on an error level of the power supplied to the power grid that is greater than the first predetermined threshold during a first cycle of the recovery phase, and wherein the second torque command is generated based on an error level of the power supplied to the power grid that is greater than a second predetermined threshold during a second cycle of the recovery phase that follows the first cycle of the recovery phase.

[0073] Clause 15. The system according to any of the preceding clauses, wherein the second predetermined threshold is less than the first predetermined threshold.

[0074] Clause 16. The system according to any of the preceding clauses, further comprising: generating the second torque command based on an error level of the power supplied to the power grid that is greater than a third predetermined threshold during a third cycle of the recovery phase that follows the second cycle of the recovery phase.

[0075] Clause 17. The system according to any of the preceding clauses, 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 according to any of the preceding clauses, wherein the first time period and the second time period are determined based on timer logic.

[0077] Clause 19. The system according to any of the preceding clauses, wherein the timer logic generates time pulses based on an estimated torque generation time in the drive train, and wherein the time pulses correspond to the period of drive train load oscillation.

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

Claims

1. A method for controlling a wind turbine coupled to a power grid, the wind turbine having a drive train including a rotor rotatably coupled to a generator via a slip coupling, the method comprising: Detecting a transient grid event via a controller; Generating, in response to the transient grid event, one or more torque commands via a drive train damper control module of the controller; And Driving the generator based on the one or more torque commands to provide torque, whereby torsional vibrations caused by the transient grid event are damped and the error magnitude of the power supplied to the power grid during a recovery phase after the transient grid event is minimized.

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

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

4. The method according to claim 3, wherein, The predetermined threshold is a first predetermined threshold, wherein the second torque command is generated based on the error level of the power supplied to the power grid that is 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 the power supplied to the power grid that is 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 according to claim 4, wherein, The second predetermined threshold is less than the first predetermined threshold.

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

7. The method according to 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 according to claim 2, wherein The first time period and the second time period are determined based on timer logic.

9. The method according to claim 8, wherein The timer logic generates time pulses based on an estimated torque generation time in the drive train, and wherein the time pulses correspond to the period of drive train load oscillations.

10. The method according to claim 2, further comprising: Monitor the torque in the drive train, compare the torque in the drive train with the nominal release threshold of the slip coupling, and drive 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 drive train including a generator rotatably coupled to a rotor via a slip coupling; And A controller communicatively coupled to the generator, the controller including at least one processor configured to perform a plurality of operations, the plurality of operations including: Detect a transient grid event; Generate one or more torque commands via a drive train damper control module of the controller in response to the transient grid event; and Drive the generator to provide torque based on the one or more torque commands, whereby torsional vibrations caused by the transient grid event are damped and the error magnitude of the power supplied to the power grid during a recovery phase after the transient grid event is minimized.

12. The system according to 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 includes: generating a first torque command configured to damp torsional vibrations caused by the transient grid event; and generating a second torque command configured to minimize the error magnitude of the power supplied to the power grid during a recovery phase immediately following the transient grid event, wherein driving the generator to provide torque based on the one or more torque commands includes: driving the generator to provide a first torque for a first time period based on the first torque command; and driving the generator to provide a second torque for a second time period based on the second torque command, wherein generating the first torque command includes applying a first gain in a closed-loop control algorithm, and wherein generating the second torque command includes applying a second gain in the closed-loop control algorithm.

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

14. The system according to claim 13, wherein, The predetermined threshold is a first predetermined threshold, wherein the second torque command is generated based on the error level of the 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 the 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 according to claim 14, wherein, The second predetermined threshold is less than the first predetermined threshold.

16. The system according to claim 14, further comprising: Generate the second torque command based on an error level of the 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 the recovery phase.

17. The system according to 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 according to claim 12, wherein The first time period and the second time period are determined based on timer logic.

19. The system according to claim 18, wherein The timer logic generates time pulses based on the estimated torque in the driveline, and wherein the time pulses correspond to the period of the driveline load oscillation.

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

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