Drivetrain damper for a wind turbine power system

Abstract

A method of damping drivetrain oscillations in a wind turbine power system connected to an electrical grid includes receiving, via a drivetrain damping algorithm, an energy buffer power command for an energy buffer of the wind turbine power system. The method also includes modulating, via the drivetrain damping algorithm, the energy buffer power command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals include at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so as to dampen the drivetrain oscillations without directly controlling power or torque on a generator of the wind turbine power system.

Description

700829-WO-1 / GECW-1261-PCTDRIVETRAIN DAMPER FOR A WIND TURBINE POWER SYSTEMFIELD

[0001] The present disclosure relates in general to wind turbines, and more particularly to a drivetrain damper for a wind turbine power system.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, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is typically geared to a generator for producing electricity.

[0003] Wind turbines can be distinguished in two types: fixed speed and variable speed turbines. Conventionally, variable speed wind turbines are controlled as current sources connected to a power grid. In other words, the variable speed wind turbines rely on a grid frequency detected by a phase locked loop (PLL) as a reference and inject a specified amount of current into the grid. The conventional current source control of the wind turbines is based on the assumptions that the grid voltage waveforms are fundamental frequency voltage waveforms with fixed frequency and magnitude and that the penetration of wind power into the grid is low enough so as to not cause disturbances to the grid voltage magnitude and frequency. Thus, the wind turbines simply inject the specified current into the grid based on the fundamental voltage waveforms. However, with the rapid growth of the wind power, wind power penetration into some grids has increased to the point where wind turbine generators have a significant impact on the grid voltage and frequency. When wind turbines are located in a weak grid, wind turbine power fluctuations may lead to an increase in magnitude and frequency variations in the grid voltage. These fluctuations may700829-WO-1 / GECW-1261-PCT adversely affect the performance and stability of the PLL and wind turbine current control.

[0004] Furthermore, many existing renewable generation converters, such as double-fed wind turbine generators, operate in a “grid-following” mode. Gridfollowing (GFL) type devices utilize fast current-regulation loops to control active and reactive power exchanged with the grid. More specifically. FIG. 1 illustrates the basic elements of the main circuit and converter control structure for a grid-following double-fed wind turbine generator. As shown, the active pow er reference to the converter is developed by the energy source regulator, e.g., the turbine control portion of a wind turbine. This is conveyed as a torque reference which represents the lesser of the maximum attainable power from the energy source at that instant, or a curtailment command from a higher-level grid controller. The converter control then determines a current reference for the active component of current to achieve the desired torque. Accordingly, the double-fed wind turbine generator includes functions that manage the voltage and reactive power in a manner that results in a command for the reactive component of current. Wide-bandwidth current regulators then develop commands for voltage to be applied by the converters to the system, such that the actual currents closely track the commands.

[0005] Alternatively, grid-forming (GFM) ty pe converters provide a voltagesource characteristic, where the angle and magnitude of the voltage are controlled to achieve the regulation functions needed by the grid. With this structure, current will flow according to the demands of the grid while the converter contributes to establishing a voltage and frequency for the grid. This characteristic is comparable to conventional generators based on a turbine driving a synchronous machine. Thus, a GFM source must include the following basic functions: (1) support grid voltage and frequency for any current flow within the rating of the equipment, both real and reactive; (2) prevent operation beyond equipment voltage or current capability by allowing grid voltage or frequency to change rather than disconnecting equipment (disconnection is allowed only when voltage or frequency are outside of bounds established by the grid entity); (3) remain stable for any grid configuration or load characteristic, including serving an isolated load or connected with other grid-forming sources, and switching between such configurations; (4) share total load of the grid700829-WO-1 / GECW-1261-PCT among other grid-forming sources connected to the grid; (5) ride through grid disturbances, both major and minor, and (6) meet requirements (1 )-(5) without requiring fast communication with other control systems existing in the grid, or externally-created logic signals related to grid configuration changes.

[0006] The basic control structure to achieve the above GFM objectives was developed and field-proven for battery systems in the early 1990's (see e.g., United States Patent No.: 5,798.633 entitled ‘"Battery Energy Storage Power Conditioning System”). Applications to full-converter wind generators and solar generators are disclosed in United States Publication No.: 2010 / 0142237 entitled “System and Method for Control of a Grid Connected Power Generating System,” and United States Patent No.: 9,270,194 entitled “Controller for controlling a power converter.” However, such implementations have been employed on full-converter wind generators.

[0007] Wind turbines have various natural oscillation modes and forced oscillations associated with drivetrain torsional oscillation mode, tower oscillation modes, and / or forced oscillations due to blade movement. In modem wind turbines, these oscillations made be damped or otherwise manifest as modulation of grid power injected by the wind turbine. In typical grid connections, this modulation in power is achieved by changing the electrical angle of the wind turbine which produces a corresponding change in power. Practically, this change in angle occurs due to changes in torque command, active power command, or active current command.

[0008] In situations where the grid is very weak or the wind turbine is operating in an islanding or blackstart condition, for example, the typical relationship between wind turbine power injection and angle may be partially or entirely “broken” and may limit the ability to change power / torque directly.

[0009] Accordingly, the present disclosure is directed to a system and method for using an energy buffer to provide the power / energy for the associated drivetrain oscillation to overcome the constraints of the grid. More specifically, systems and methods of the present disclosure is directed to a drivetrain damping function associated with the main drivetrain torsional oscillation mode, as well as other types of oscillations described herein.700829-WO-1 / GECW-1261-PCTBRIEF DESCRIPTION

[0010] 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.

[0011] In an aspect, the present disclosure is directed to a method of damping drivetrain oscillations in a wind turbine power system connected to an electrical grid. The method includes receiving, via a drivetrain damping algorithm, an energy buffer power command for an energy buffer of the wind turbine power system. The method also includes modulating, via the drivetrain damping algorithm, the energy buffer power command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals comprise at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so as to dampen the drivetrain oscillations without directly controlling power or torque on a generator of the wind turbine power system.

[0012] In another aspect, the present disclosure is directed to a wind turbine including a generator, a power converter coupled to the generator, an energy buffer, and a controller. The controller includes at least one processor configured to perform a plurality of operations, including but not limited to receiving, via a drivetrain damping algorithm programmed in the controller, an energy buffer power command for the energy buffer; and modulating, via the drivetrain damping algorithm, the energy buffer power command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals comprise at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so as to dampen the drivetrain oscillations without directly controlling power or torque on the generator.

[0013] 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.700829-WO-1 / GECW-1261-PCTBRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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:

[0015] FIG. 1 illustrates a one-line diagram of a double-fed wind turbine generator with structure of converter controls for grid-following application according to conventional construction;

[0016] FIG. 2 illustrates a perspective view of an embodiment of a wind turbine according to the present disclosure;

[0017] FIG. 3 illustrates a simplified, internal view of an embodiment of a nacelle according to the present disclosure;

[0018] FIG. 4 illustrates a schematic view of an embodiment of a wind turbine electrical power system suitable for use with the wind turbine shown in FIG. 1;

[0019] FIG. 5 illustrates a schematic view of an embodiment of a wind farm having a plurality of wind turbines according to the present disclosure;

[0020] FIG. 6 illustrates a block diagram of an embodiment of a controller according to the present disclosure;

[0021] FIG. 7 illustrates a one-line diagram of a double-fed wind turbine generator with converter controls for grid-forming application according to the present disclosure;

[0022] FIG. 8 illustrates a schematic diagram of an embodiment of a drivetrain damping approach;

[0023] FIG. 9 illustrates a flow' diagram of an embodiment of a method of damping drivetrain oscillations in a wind turbine power system connected to an electrical grid according to the present disclosure;

[0024] FIG. 10 illustrates a schematic diagram of an embodiment of hardw are structure having an energy buffer to accommodate advanced drivetrain damping according to the present disclosure;

[0025] FIG. 11 illustrates a schematic diagram of an embodiment of control of an energy buffer to achieve drivetrain damping according to the present disclosure;

[0026] FIG. 12 illustrates a schematic diagram of an embodiment of grid following control w ith added function to increase sensitivity of drivetrain torque to700829-WO-1 / GECW-1261-PCT changes in grid frequency / angle at the drivetrain frequency according to the present disclosure; and

[0027] FIG. 13 illustrates a schematic diagram of an embodiment of a grid forming inertial power regulator with modifications to cancel changes in power introduced by the energy storage based drivetrain damper according to the present disclosure.

[0028] 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

[0029] Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of an embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0030] As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components.

[0031] 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.

[0032] 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”, and “substantially”, are not to be limited to the precise value specified. In at least700829-WO-1 / GECW-1261-PCT 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.

[0033] 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.

[0034] Generally, the present disclosure is directed to systems and methods of damping drivetrain oscillations in a wind turbine power system connected to an electrical grid according to the present disclosure. In particular, systems of the present disclosure include an additional energy buffer within the wind turbine. In such embodiments, an energy buffer power command is modulated based on a drivetrain damper command. The energy buffer power command is modulated around a state of charge control command from other regulators (if the energy buffer is a battery energy storage device, for example). Modulating the energy buffer power together with rotor converter control commands that are sensitive to changes in either the total power injected and / or the electrical angle / frequency at the drivetrain frequency produces the desired damping effect without directly controlling power / torque of the generator based on the drivetrain damper command.

[0035] Referring now to the drawings, FIG. 2 illustrates a perspective view of an embodiment of a wind turbine 10 according to the present disclosure. As shown, the wind turbine 10 generally includes a tower 12 extending from a support surface 14, a nacelle 16 mounted on the tower 12. and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in an alternative embodiment, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub 20 may be rotatably coupled to700829-WO-1 / GECW-1261-PCT an electric generator 24 (FIG. 3) positioned within the nacelle 16 to permit electrical energy to be produced.

[0036] The wind turbine 10 may also include a wind turbine controller 26 centralized within the nacelle 16. However, in other embodiments, the controller 26 may be located within any other component of the wind turbine 10 or at a location outside the wind turbine 10. Further, the controller 26 may be communicatively coupled to any number of the components of the wind turbine 10 in order to control the operation of such components and / or implement a corrective or control action. As such, the controller 26 may include a computer or other suitable processing unit. Thus, in several embodiments, the controller 26 may include suitable computer- readable instructions that, when implemented, configure the controller 26 to perform various different functions, such as receiving, transmitting and / or executing wind turbine control signals. Accordingly, the controller 26 may generally be configured to control the various operating modes (e.g., start-up or shut-do wn sequences), de-rating or up-rating the wind turbine, and / or individual components of the wind turbine 10.

[0037] Referring now to FIG. 2. a simplified, internal view of an embodiment of the nacelle 16 of the wind turbine 10 shown in FIG. 1 is illustrated. As shown, a generator 24 may be disposed within the nacelle 16 and supported atop a bedplate 46. In general, the generator 24 may be coupled to the rotor 18 for producing electrical power from the rotational energy generated by the rotor 18. For example, as shown in the illustrated embodiment, the rotor 18 may include a rotor shaft 34 coupled to the hub 20 for rotation therewith. The rotor shaft 34 may, in turn, be rotatably coupled to a generator shaft 36 of the generator 24 through a gearbox 38. As is generally understood, the rotor shaft 34 may provide a low speed, high torque input to the gearbox 38 in response to rotation of the rotor blades 22 and the hub 20. The gearbox 38 may then be configured to convert the low speed, high torque input to a high speed, low torque output to drive the generator shaft 36 and, thus, the generator 24.

[0038] The wind turbine 10 may also one or more pitch drive mechanisms 32 communicatively coupled to the wind turbine controller 26. with each pitch adjustment mechanism(s) 32 being configured to rotate a pitch bearing 40 and thus the individual rotor blade(s) 22 about its respective pitch axis 28. In addition, as shown, the wind turbine 10 may include one or more yaw drive mechanisms 42700829-WO-1 / GECW-1261-PCT configured to change the angle of the nacelle 16 relative to the wind (e.g., byengaging a yaw bearing 44 of the wind turbine 10 that is arranged between the nacelle 16 and the tower 12 of the wind turbine 10).

[0039] In addition, the wind turbine 10 may also include one or more sensors 66, 68 for monitoring various wind conditions of the wind turbine 10. For example, the incoming wind direction 52, wind speed, or any other suitable wind condition near of the wind turbine 10 may be measured, such as through use of a suitable weather sensor 66. Suitable weather sensors may include, for example, Light Detection and Ranging (“LIDAR’’) devices, Sonic Detection and Ranging (“SOD AR”) devices, anemometers, wind vanes, barometers, radar devices (such as Doppler radar devices) or any other sensing device which can provide wind directional information now known or later developed in the art. Further sensors 68 may be utilized to measure additional operating parameters of the wind turbine 10, such as voltage, current, vibration, etc. as described herein.

[0040] Referring now to FIG. 4, a schematic diagram of an embodiment of a wind turbine power system 100 is illustrated in accordance with aspects of the present disclosure. Although the present disclosure will generally be described herein with reference to the system 100 show n in FIG. 4, those of ordinary skill in the art, using the disclosures provided herein, should understand that aspects of the present disclosure may also be applicable in other power generation systems, and, as mentioned above, that the invention is not limited to wind turbine systems.

[0041] In the embodiment of FIG. 4 and as mentioned, the rotor 18 of the wind turbine 10 (FIG. 2) may, optionally, be coupled to the gearbox 38, which is, in turn, coupled to a generator 102, which may be a doubly fed induction generator (DFIG). As shown, the DFIG 102 may be connected to a stator bus 104. Further, as shown, a power converter 106 may be connected to the DFIG 102 via a rotor bus 108, and to the stator bus 104 via a line side bus 110. As such, the stator bus 104 may provide an output multiphase power (e.g., three-phase power) from a stator of the DFIG 102, and the rotor bus 108 may provide an output multiphase power (e.g., three-phase power) from a rotor of the DFIG 102. The power converter 106 may also include a rotor side converter (RSC) 112 and a line side converter (LSC) 114. The DFIG 102 is coupled via the rotor bus 108 to the rotor side converter 112. Additionally, the RSC 112 is700829-WO-1 / GECW-1261-PCT coupled to the LSC 114 via a DC link 116 across which is a DC link capacitor 118. The LSC 114 is, in turn, coupled to the line side bus 110. Moreover, the wind turbine 10 may include an energy buffer 125, such as a battery energy storage device, one or more capacitors, one or more inductors, or a resistive element (such as a dynamic brake), or combinations thereof.

[0042] The RSC 112 and the LSC 114 may be configured for normal operating mode in a three-phase, pulse width modulation (PWM) arrangement using one or more switching devices, such as insulated gate bipolar transistor (IGBT) switching elements. In addition, the power converter 106 may be coupled to a converter controller 120 in order to control the operation of the rotor side converter 112 and / or the line side converter 114 as described herein. It should be noted that the converter controller 120 may be configured as an interface between the power converter 106 and the turbine controller 26 and may include any number of control devices.

[0043] In typical configurations, various line contactors and circuit breakers including, for example, a grid breaker 122 may also be included for isolating the various components as necessary for normal operation of the DFIG 102 during connection to and disconnection from a load, such as the electrical grid 124. For example, a system circuit breaker 126 may couple a system bus 128 to a transformer 130, which may be coupled to the electrical grid 124 via the grid breaker 122. In alternative embodiments, fuses may replace some or all of the circuit breakers.

[0044] In operation, alternating current power generated at the DFIG 102 by rotating the rotor 18 is provided to the electrical grid 124 via dual paths defined by the stator bus 104 and the rotor bus 108. On the rotor bus side 108, sinusoidal multiphase (e.g.. three-phase) alternating current (AC) power is provided to the power converter 106. The rotor side converter 112 converts the AC power provided from the rotor bus 108 into direct current (DC) power and provides the DC power to the DC link 116. As is generally understood, switching elements (e.g., IGBTs) used in the bridge circuits of the rotor side converter 112 may be modulated to convert the AC power provided from the rotor bus 108 into DC power suitable for the DC link 116.

[0045] In addition, the line side converter 114 converts the DC power on the DC link 116 into AC output power suitable for the electrical grid 124. In particular,700829-WO-1 / GECW-1261-PCT switching elements (e.g., IGBTs) used in bridge circuits of the line side converter 114 can be modulated to convert the DC power on the DC link 116 into AC power on the line side bus 110. The AC power from the power converter 106 can be combined with the power from the stator of DFIG 102 to provide multi-phase power (e.g., three- phase power) having a frequency maintained substantially at the frequency of the electrical grid 124 (e g., 50 Hz or 60 Hz).

[0046] Additionally, various circuit breakers and switches, such as grid breaker 122, system circuit breaker 126, stator sync switch 132, converter breaker 134, and line contactor 136 may be included in the wind turbine power system 100 to connect or disconnect corresponding buses, for example, when current flow is excessive and may damage components of the wind turbine power system 100 or for other operational considerations. Additional protection components may also be included in the wind turbine power system 100.

[0047] Moreover, the power converter 106 may receive control signals from, for instance, the local control system 176 via the converter controller 120. The control signals may be based, among other things, on sensed states or operating characteristics of the wind turbine power system 100. Typically, the control signals provide control of the operation of the power converter 106. For example, feedback in the form of a sensed speed of the DFIG 102 may be used to control the conversion of the output power from the rotor bus 108 to maintain a proper and balanced multiphase (e.g., three-phase) power supply. Other feedback from other sensors may also be used by the controller(s) 120, 26 to control the power converter 106, including, for example, stator and rotor bus voltages and current feedbacks. Using the various forms of feedback information, switching control signals (e g., gate timing commands for IGBTs), stator synchronizing control signals, and circuit breaker signals may be generated.

[0048] The power converter 106 also compensates or adjusts the frequency of the three-phase power from the rotor for changes, for example, in the wind speed at the hub 20 and the rotor blades 22. Therefore, mechanical and electrical rotor frequencies are decoupled, and the electrical stator and rotor frequency matching is facilitated substantially independently of the mechanical rotor speed.

[0049] Under some states, the bi-directional characteristics of the power converter700829-WO-1 / GECW-1261-PCT106, and specifically, the bi-directional characteristics of the LSC 114 and RSC 112, facilitate feeding back at least some of the generated electrical power into generator rotor. More specifically, electrical power may be transmitted from the stator bus 104 to the line side bus 110 and subsequently through the line contactor 136 and into the power converter 106, specifically the LSC 114 which acts as a rectifier and rectifies the sinusoidal, three-phase AC power to DC power. The DC power is transmitted into the DC link 116. The capacitor 118 facilitates mitigating DC link voltage amplitude variations by facilitating mitigation of a DC ripple sometimes associated with three- phase AC rectification.

[0050] The DC power is subsequently transmitted to the RSC 112 that converts the DC electrical power to a three-phase, sinusoidal AC electrical power by adjusting voltages, currents, and frequencies. This conversion is monitored and controlled via the converter controller 120. The converted AC power is transmitted from the RSC 112 via the rotor bus 108 to the generator rotor. In this manner, generator reactive power control is facilitated by controlling rotor current and voltage.

[0051] Referring now to FIG. 5. the wind turbine power system 100 described herein may be part of a wind farm 50. As shown, the wind farm 50 may include a plurality of wind turbines 52, including the wind turbine 10 described above, and an overall farm-level controller 56. For example, as shown in the illustrated embodiment, the wind farm 50 includes twelve wind turbines, including wind turbine 10. However, in other embodiments, the wind farm 50 may include any other number of wind turbines, such as less than twelve wind turbines or greater than twelve wind turbines. In an embodiment, the turbine controllers of the plurality of wind turbines 52 are communicatively coupled to the farm-level controller 56, e.g., through a wired connection, such as by connecting the turbine controller 26 through suitable communicative links 54 (e g., a suitable cable). Alternatively, the turbine controllers may be communicatively coupled to the farm-level controller 56 through a wireless connection, such as by using any suitable wireless communications protocol known in the art. In further embodiments, the farm-level controller 56 is configured to send and receive control signals to and from the various wind turbines 52, such as for example, distributing real and / or reactive pow er demands across the wand turbines 52 of the wind farm 50.700829-WO-1 / GECW-1261-PCT

[0052] Referring now to FIG. 6, a block diagram of an embodiment of suitable components that may be included within the controller (such as any one of the converter controller 120. the turbine controller 26. and / or the farm-level controller 56 described herein) in accordance with example aspects of the present disclosure is illustrated. As shown, the controller may include one or more processor(s) 58, computer, or other suitable processing unit and associated memory device(s) 60 that may include suitable computer-readable instructions that, when implemented, configure the controller to perform various different functions, such as receiving, transmitting and / or executing wind turbine control signals (e.g., performing the methods, steps, calculations and the like disclosed herein).

[0053] 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) 60 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.

[0054] Such memory device(s) 60 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 58, configure the controller to perform various functions as described herein. Additionally, the controller may also include a communications interface 62 to facilitate communications between the controller and the various components of the wind turbine 10. An interface can include one or more circuits, terminals, pins, contacts, conductors, or other components for sending and receiving control signals. Moreover, the controller may include a sensor interface 64 (e.g., one or more analog- to-digital converters) to permit signals transmitted from the sensors 66, 68 to be converted into signals that can be understood and processed by the processor(s) 58.

[0055] Referring now to FIG. 7, a schematic diagram of an embodiment of a grid forming power system 200 according to the present disclosure, particularly illustrating a one-line diagram of the double-fed w ind turbine generator 102 with a high-level700829-WO-1 / GECW-1261-PCT control structure for grid-forming characteristics. In particular, as shown, the grid forming power system 200 may include many of the same features of FIG. 4 described herein, with components having the same reference characters representing like components. Further, as shown, the grid forming power system 200 may include a control structure for controlling the line side converter that is similar to the control structure shown in FIG. 1. More particularly, as shown, the line side converter control structure may include a DC regulator 212 and a line current regulator 214. The DC regulator 212 is configured to generate line-side current commands for the line current regulator 214. The line current regulator 214 then generates line-side voltage commands for a modulator 218. The modulator 218 also receives an output (e.g., a phase-locked loop (PLL) angle) from a PLL 216 to generate one or more gate pulses for the line side converter 1 14. The PLL 216 typically generates its output using a voltage feedback signal.

[0056] Furthermore, as shown, the grid forming power system 200 may also include a unique control structure for controlling the rotor side converter 112 using grid-forming characteristics. In particular, as shown in FIG. 7, the grid forming power system 200 may include a stator voltage regulator 206 for providing such gridforming characteristics. In addition, as showm, the grid forming power system 200 may include a grid voltage / V AR regulator 202, an inertial power regulator 204, a rotor current regulator 208, and a modulator 210. Thus, in an embodiment, a drivetrain damping algorithm 220 (FIG. 8) exists within the inertial power regulator 204. In an embodiment, as shown in FIG. 8, the drivetrain damping algorithm 220 is configured to generate a torque command 222 (e.g., DTDTrqCmd) that is summed together with a main torque reference 224 (e.g., Torque_Ref) from the turbine control to determine a torque command 226 (e.g.. TrqCmd). Alternatively, a similar drivetrain damping algorithm may be configured to generate a power command based on the drivetrain damper torque command 222 and a speed feedback and summed with the inertial power regulator reference (e.g. POWER REF) to determine an angle command for a stator voltage regulator (e.g. VS ANGLE Cmd). It should be further understood that although FIGS. 7 and 8 illustrate the drivetrain damping algorithm 220 existing within the converter control, it can equivalently be applied in the upstream turbine control. This approach to drivetrain damping is achieved, therefore,700829-WO-1 / GECW-1261-PCT by directly controlling torque on the generator.

[0057] Referring now to FIGS. 9-13, the present disclosure is directed to a method 250 and a system 300 for damping drivetrain oscillations in a wind turbine power system connected to an electrical grid according to the present disclosure. In particular, FIG. 9 illustrates a flow diagram of an embodiment of a method 250 of damping drivetrain oscillations in a wind turbine power system connected to an electrical grid according to the present disclosure. In general, the method 250 is described herein with reference to the wind turbine 10 and the wind farm 50 of FIGS. 2-8. However, it should be appreciated that the disclosed method 250 may be implemented with any wind turbines having any other suitable configurations. In addition, although FIG. 9 depicts steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods disclosed herein can be omitted, rearranged, combined, and / or adapted in various ways without deviating from the scope of the present disclosure.

[0058] As shown at (252), the method 250 includes receiving, via a drivetrain damping algorithm, an energy buffer power command for an energy buffer, such as energy buffer 125 described herein. As shown at (254), the method 250 includes modulating, via the drivetrain damping algorithm, the energy buffer power command based on a drivetrain damper command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals comprise at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so as to dampen the drivetrain oscillations without directly controlling power or torque on a generator of the wind turbine power system.

[0059] The method 250 of FIG. 9 can be better understood with reference to FIGS. 10-13. In particular, FIGS. 10-13 illustrate schematic diagrams of the system 300 for damping drivetrain oscillations in a wind turbine power system connected to an electrical grid according to the present disclosure. More specifically, FIGS. 10 and 11 illustrate schematic diagrams of an embodiment of the system 300 having a hardware structure with an energy buffer 302 to accommodate the advanced DTD.700829-WO-1 / GECW-1261-PCT

[0060] Accordingly, as shown, the system 300 may include the additional energybuffer 302 with a corresponding energy buffer control module 304 within the wind turbine 10. In such embodiments, instead of using the drivetrain damper 220 (FIG. 8) to modulate the torque command 226, an energy buffer power command 306 (e.g., PebCmd) is modulated based on a drivetrain damper command 308 (e.g., DTDTrqCmd) using the drivetrain damping algorithm of the energy buffer control module 304. Further, in an embodiment, the energy buffer power command 306 is modulated around a state of charge control command 310 (e g., Psoc) from other regulators.

[0061] More specifically, in an embodiment, as shown in FIG. 11, the drivetrain damping algorithm is configured to modulate the energy buffer power command 306 by receiving one or more feedback signals 314 (such as a speed feedback signal) and filtering the feedback signal(s) 314 via a filter 316 to obtain one or more filtered signals 318. Further, as shown, the drivetrain damping algorithm is configured to modulate the energy buffer power command 306 by determining the drivetrain damper command 308 based on the feedback signal(s) 314 and multiplying the drivetrain damper command 308 by the filtered signal 318 to obtain a processed signal 320. Thus, as shown, the drivetrain damping algorithm sums the processed signal 320 and the state of charge control command 310 to modulate the energy buffer power command 306.

[0062] Accordingly, modulating the energy buffer power command 306 together with rotor-side controls 312 (see e.g., FIG. 10) that are sensitive to changes in either the total power injected (PT) and / or the electrical angle / frequency at the drivetrain frequency produces the desired damping effect.

[0063] The concept can be understood from the balance of power equation given by Equation (1) below:APT=APS-APR+APEB Equation (1)

[0064] If the energy buffer power (e.g., APEB) injected is appropriately cancelled by the associated power of the wind turbine drivetrain (reflected as the combination of APS and APR in Equation (1)), the total pow er injected into the grid at the drivetrain700829-WO-1 / GECW-1261-PCT frequency will be approximately zero and the desired changed in power / torque on the drivetrain to achieve the damping effect will be realized.

[0065] Referring now to FIGS. 12 and 13. rotor-side controls for achieving the desired sensitivity to the total power and / or electrical frequency / angle in both grid following and grid forming applications is further explained. In particular, FIG. 12 illustrates a schematic diagram of an embodiment of grid following control 400 with added function to increase sensitivity of drivetrain torque to changes in grid frequency / angle at the drivetrain frequency according to the present disclosure. FIG. 13 illustrates a schematic diagram of an embodiment of a grid forming inertial power regulator 500 with modifications to cancel changes in power introduced by the energy storage based drivetrain damper according to the present disclosure.

[0066] Referring particularly to FIG. 12, in some grid following applications, open loop control of power / torque may be used, making the controls relatively insensitive to the total power feedback 402 (e.g., P k). Accordingly, as shown, the grid following control 400 of the present disclosure is configured to selectively introduce this sensitivity (represented in FIG. 12 as signal DtPwrModTrq 410) but only at the associated drivetrain frequency(s) using a bandpass filter 404.Additionally, in an embodiment, various limits and rate limits 406 can be applied to the total power feedback so as to respond only to small-signal changes in pow er to mitigate response to large grid events (e.g., grid faults).

[0067] Furthermore, in an embodiment, grid following controls are typically designed to be relatively insensitive to small changes in grid frequency / angle. Therefore, the grid follow ing control 400 of the present disclosure is further configured to introduce this sensitivity (represented in FIG. 12 as signal DtAngModTrq 412) to the grid frequency and / or the grid angle within a narrow frequency range of interest of the associated drivetrain frequency(s).

[0068] For example, in an embodiment, as shown in FIG. 12, the grid following control 400 of the present disclosure is configured to introduce the sensitivity by passing the voltage feedback through a phase-locked loop (PLL) 418 to determine a phase-locked loop error 420 (e.g., PllErr). Moreover, in an embodiment, as shown, the grid follow ing control 400 of the present disclosure is configured to apply one or more rate limits 414 and output limits to the phase-locked loop error 420 to determine700829-WO-1 / GECW-1261-PCT a limited value 422, e.g., for similar reasons at the power path. In addition, as shown, the grid following control 400 of the present disclosure is configured to filter the limited value 422 via at least one filter 416, such as a bandpass filter. Furthermore, in an embodiment, a gain of the bandpass filter 416 may be adjusted based on applications where an increased sensitivity may be needed for stronger grid applications and a lower gain may be sufficient for weaker grid applications. In certain embodiments, only one of the two modifications (e.g.. introducing one or more of signals DtPwrModTrq 410 or DtAngModTrq 412) may be utilized.

[0069] Referring now to FIG. 13, the grid forming inertial power regulator 500 includes grid-forming power feedforward control according to the present disclosure. Thus, as shown, the inertial power regulator 500 receives a power reference Pref and a power command limits PcmdLimits from a higher-level controller (e.g., the turbine controller 26 and / or the farm-level controller 56). These high-level limits are on physical quantities of voltage, current, and power. Thus, as shown, the inertial pow er regulator 500 has final limits applied to the converter control commands for power angle (e.g.. 0pang) to implement constraints on real components of current, respectively. In particular, as shown in FIG. 13, the inertial power regulator 500 provides rapid response to control commands using a feedforward path 506 and a pow er limit function 508. Accordingly, the converter gating logic of FIG. 13 is configured to create a converter voltage with an angle based upon the control signal Op ng and OPI.L. In other embodiments, the voltage with angle based on 0pangand 0PI,L may be created by other equipment capability of creating a voltage phasor.

[0070] Still referring to FIG. 13, to minimize latency in variations in the power command, the grid forming inertial power regulator 500 is configured to calculate a feedforward angle (i.e., Opangff). Thus, as shown, the feedforward angle Opangff (e.g.. in radians) can be differentiated to obtain an angle rate of change in frequency (e g., copangff with units of radians / second). Further, as shown, the angle rate of change can then be summed with frequency signals (e.g., copreg and COPLL). The outputs of these summations can then be integrated to obtain the final angles (i.e., 0pangand 0PLL) of the converter and the PLL.

[0071] Unlike grid following controls, the grid forming inertial powder regulator 500 (FIG. 13) is inherently sensitive to changes in grid frequency / angle.700829-WO-1 / GECW-1261-PCTAdditionally, the grid forming inertial power regulator 500 may already regulate the total power output. Therefore, modification(s) needed to accommodate the energy buffer based drivetrain damper described herein may include certain filtering to adjust the gain / phase angle of the grid forming inertial power regulator 500 at the drivetrain frequency(s) to more effectively cancel the changes in power introduced by the energy buffer 302. For example, as shown in FIG. 13, the grid forming inertial power regulator 500 may be configured to filter, via at least one filter 502. a power error signal 504 (e g., Perr) when the wind turbine 10 is under grid forming control to adjust at least one of a gain or a phase angle of the inertial power regulator 500 at one or more drivetrain frequencies to more effectively cancel changes in power introduced by the energy buffer. More specifically, in an embodiment, a lead / lag filter 502 may be included to the grid forming inertial power regulator 500 to reduce the natural phase lag thereof at the drivetrain frequency to better cancel the power injected in the grid at the drivetrain frequency while also increase the effectiveness of the damping function.

[0072] 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.

[0073] Further aspects of the invention are provided by the subject matter of the following clauses:

[0074] A method of damping drivetrain oscillations in a wind turbine power system connected to an electrical grid, the method comprising: receiving, via a drivetrain damping algorithm, an energy buffer power command for an energy buffer700829-WO-1 / GECW-1261-PCT of the wind turbine power system; and modulating, via the drivetrain damping algorithm, the energy’ buffer power command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals comprise at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so as to dampen the drivetrain oscillations without directly controlling power or torque on a generator of the wind turbine power system.

[0075] The method of any preceding clause, wherein modulating, via the drivetrain damping algorithm, the energy buffer power command further comprises modulating the energy buffer power command around a state of charge control command.

[0076] The method of any preceding clause, wherein modulating the energy buffer power command further comprises: receiving one or more feedback signals; filtering the one or more feedback signals to obtain one or more filtered signals; determining a drivetrain torque command based on at least one of the one or more feedback signals or the one or more filtered signals; multiplying the drivetrain torque command by the filtered signal to obtain a processed signal; and summing the processed signal and the state of charge control command to modulate the energy' buffer power command.

[0077] The method of any preceding clause, wherein the one or more feedback signals comprises a speed feedback signal.

[0078] The method of any preceding clause, further comprising filtering, via at least one filter, a power error signal of an inertial power regulator when the wind turbine power system is under grid forming control to adjust at least one of a gain or a phase angle of the inertial power regulator at one or more drivetrain frequencies to more effectively cancel changes in power introduced by7the energy buffer.

[0079] The method of any preceding clause, wherein the at least one filter comprises a lead / lag filter to reduce a phase lag of the inertial power regulator at the one or more drivetrain frequencies.

[0080] The method of any preceding clause, further comprising selectively introducing sensitivity to a total power feedback.

[0081] The method of any preceding clause, wherein selectively introducing the700829-WO-1 / GECW-1261-PCT sensitivity to the total power feedback further comprises selectively introducing the sensitivity to the total power feedback only at one or more associated drivetrain frequencies using a bandpass fdter.

[0082] The method of any preceding clause, further comprising applying one or more limits or rate limits to the total power feedback to respond only to small signal changes in the total power feedback so as to mitigate a response to grid faults.

[0083] The method of any preceding clause, further comprising introducing sensitivity to at least one of grid frequency or grid angle within a narrow frequency range of interest of one or more associated drivetrain frequencies.

[0084] The method of any preceding clause, wherein introducing the sensitivity to at least one of grid frequency or the grid angle within the narrow frequency range of interest of one or more associated drivetrain frequencies further comprises: passing a voltage feedback through a phase-locked loop to determine a phase-locked loop error; applying one or more rate limits to the phase-locked loop error to determine a limited value; and filtering the limited value via at least one filter.

[0085] The method of any preceding clause, wherein the at least one filter comprises a bandpass filter.

[0086] The method of any preceding clause, further comprising adjusting a gain of the bandpass filter based on applications where an increased sensitivity is needed for stronger grid applications and a lower gain is sufficient for weaker grid applications.

[0087] The method of any preceding clause, wherein the energy' buffer comprises at least one of a battery energy storage system, capacitor, inductor, or resistive device.

[0088] A wind turbine, comprising: a generator; a power converter coupled to the generator; an energy buffer; and a controller comprising at least one processor configured to perform a plurality of operations, the plurality of operations comprising: receiving, via a drivetrain damping algorithm programmed in the controller, an energy' buffer power command for the energy buffer; and modulating, via the drivetrain damping algorithm, the energy buffer power command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals comprise at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so700829-WO-1 / GECW-1261-PCT as to dampen the drivetrain oscillations without directly controlling power or torque on the generator.

[0089] The wind turbine of any preceding clause, wherein modulating the energy buffer power command further comprises: receiving one or more speed feedback signals; fdtering the one or more speed feedback signals to obtain one or more filtered signals; determining a drivetrain torque command based on the one or more speed feedback signals; multiplying the drivetrain torque command by the filtered signal to obtain a processed signal; and summing the processed signal and a state of charge control command to modulate the energy buffer power command.

[0090] The wind turbine of any preceding clause, wherein the plurality of operations further comprise filtering, via at least one lead / lag filter, a power error signal of an inertial power regulator when the wind turbine is under grid forming control to adjust at least one of a gain or a phase angle of the inertial power regulator at one or more drivetrain frequencies to more effectively cancel changes in power introduced by the energy buffer.

[0091] The wind turbine of any preceding clause, wherein the plurality of operations further comprise selectively introducing sensitivity to a total power feedback when the wind turbine is under grid following control, wherein selectively introducing the sensitivity to the total power feedback when the wind turbine is under grid following control further comprises selectively introducing the sensitivity to the total power feedback only at one or more associated drivetrain frequencies using a bandpass filter.

[0092] The wind turbine of any preceding clause, further comprising applying one or more rate limits to the total power feedback to respond only to small signal changes in the total power feedback so as to mitigate a response to grid faults.

[0093] The wind turbine of any preceding clause, further comprising introducing sensitivity to at least one of grid frequency or grid angle within a narrow frequency range of interest of one or more associated drivetrain frequencies, wherein introducing the sensitivity to at least one of grid frequency or the grid angle within the narrow frequency range of interest of one or more associated drivetrain frequencies further comprises: passing at least one of the grid frequency or the grid angle through a phase-locked loop to determine a phase-locked loop error; applying one or more rate700829-WO-1 / GECW-1261-PCT limits to the phase-locked loop error to determine a limited value; and filtering the limited value via at least one bandpass filter.

[0094] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

700829-WO-1 / GECW-1261-PCTWHAT IS CLAIMED IS:

1. A method of damping drivetrain oscillations in a wind turbine power system connected to an electncal grid, the method comprising: receiving, via a drivetrain damping algorithm, an energy buffer power command for an energy buffer of the w ind turbine power system; and modulating, via the drivetrain damping algorithm, the energy buffer power command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals comprise at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so as to dampen the drivetrain oscillations without directly controlling power or torque on a generator of the wind turbine power system.

2. The method of claim 1, wherein modulating, via the drivetrain damping algorithm, the energy buffer power command further comprises modulating the energy buffer power command around a state of charge control command.

3. The method of claim 1. wherein modulating the energy buffer power command further comprises: receiving one or more feedback signals; filtering the one or more feedback signals to obtain one or more filtered signals; determining a drivetrain torque command based on at least one of the one or more feedback signals or the one or more filtered signals; multiplying the drivetrain torque command by the filtered signal to obtain a processed signal; and summing the processed signal and the state of charge control command to modulate the energy buffer power command.

4. The method of claim 3, wherein the one or more feedback signals comprises a speed feedback signal.

5. The method of claim 1. further comprising filtering, via at least one filter, a power error signal of an inertial power regulator when the wind turbine power system is under grid forming control to adjust at least one of a gain or a phase angle of the inertial pow er regulator at one or more drivetrain frequencies to more effectively700829-WO-1 / GECW-1261-PCT cancel changes in power introduced by the energy buffer.

6. The method of claim 5. wherein the at least one filter comprises a lead / lag filter to reduce a phase lag of the inertial power regulator at the one or more drivetrain frequencies.

7. The method of claim 1, further comprising selectively introducing sensitivity to a total power feedback.

8. The method of claim 7, wherein selectively introducing the sensitivity to the total power feedback further comprises selectively introducing the sensitivity to the total power feedback only at one or more associated drivetrain frequencies using a bandpass filter.

9. The method of claim 7, further comprising applying one or more limits or rate limits to the total power feedback to respond only to small signal changes in the total power feedback so as to mitigate a response to grid faults.

10. The method of claim 1, further comprising introducing sensitivity to at least one of grid frequency or grid angle within a narrow frequency range of interest of one or more associated drivetrain frequencies.

11. The method of claim 10, wherein introducing the sensitivity to at least one of grid frequency or the grid angle within the narrow frequency range of interest of one or more associated drivetrain frequencies further comprises: passing a voltage feedback through a phase-locked loop to determine a phase- locked loop error; applying one or more rate limits to the phase-locked loop error to determine a limited value; and filtering the limited value via at least one filter.

12. The method of claim 1. wherein the at least one filter comprises a bandpass filter.

13. The method of claim 12, further comprising adjusting a gain of the bandpass filter based on applications where an increased sensitivity is needed for stronger grid applications and a lower gain is sufficient for weaker grid applications.

14. The method of claim 1, wherein the energy buffer comprises at least one of a battery energy storage system, capacitor, inductor, or resistive device.

15. A wind turbine, comprising:700829-WO-1 / GECW-1261-PCT a generator; a power converter coupled to the generator; an energy buffer; and a controller comprising at least one processor configured to perform a plurality of operations, the plurality of operations comprising: receiving, via a drivetrain damping algorithm programmed in the controller, an energy buffer power command for the energy buffer; and modulating, via the drivetrain damping algorithm, the energy buffer power command in combination with providing rotor converter control commands that are sensitive to changes in electrical signals at a drivetrain frequency, wherein the electrical signals comprise at least one of total power injected into the electrical grid, an electrical angle, or an electrical frequency so as to dampen the drivetrain oscillations without directly controlling power or torque on the generator.

16. The wind turbine of claim 15, wherein modulating the energy buffer power command further comprises: receiving one or more speed feedback signals; filtering the one or more speed feedback signals to obtain one or more filtered signals; determining a drivetrain torque command based on the one or more speed feedback signals; multiplying the drivetrain torque command by the filtered signal to obtain a processed signal; and summing the processed signal and a state of charge control command to modulate the energy buffer power command.

17. The wind turbine of claim 15, wherein the plurality of operations further comprise filtering, via at least one lead / lag filter, a power error signal of an inertial power regulator when the wind turbine is under grid forming control to adjust at least one of a gain or a phase angle of the inertial power regulator at one or more drivetrain frequencies to more effectively cancel changes in power introduced by the energy buffer.

18. The wind turbine of claim 15, wherein the plurality of operations700829-WO-1 / GECW-1261-PCT further comprise selectively introducing sensitivity' to a total power feedback when the wind turbine is under grid following control, wherein selectively introducing the sensitivity to the total power feedback when the wind turbine is under grid following control further comprises selectively introducing the sensitivity to the total power feedback only at one or more associated drivetrain frequencies using a bandpass filter.

19. The wind turbine of claim 18, further comprising applying one or more rate limits to the total power feedback to respond only to small signal changes in the total power feedback so as to mitigate a response to grid faults.

20. The wind turbine of claim 15, further comprising introducing sensitivity' to at least one of grid frequency or grid angle within a narrow frequencyrange of interest of one or more associated drivetrain frequencies, wherein introducing the sensitivity to at least one of grid frequency or the grid angle within the narrow frequency range of interest of one or more associated drivetrain frequencies further comprises: passing at least one of the grid frequency or the grid angle through a phase- locked loop to determine a phase-locked loop error; applying one or more rate limits to the phase-locked loop error to determine a limited value; and filtering the limited value via at least one bandpass filter.

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