System and method to reduce blade vibrations when yawing a wind turbine that is in a shutdown state and configured with a turbine-mounted crane

Abstract

A system and method reduce vibrations in a blade mounted on a hub of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend between a turbine-mounted crane and ground-based equipment. The method determines a new yaw position for the rotor that will reduce actual or predicted vibrations in the blade; and with a wind turbine controller in communication with the yaw system and a crane controller, the rotor is yawed from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground-based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.

Description

700769-WO-1 / GECW-1264-PCTSYSTEM AND METHOD TO REDUCE BLADE VIBRATIONS WHEN YAWING A WIND TURBINE THAT IS IN A SHUTDOWN STATE AND CONFIGURED WITH A TURBINE-MOUNTED CRANEFIELD

[0001] The present disclosure relates in general to wind turbine power generating systems, and more particularly to systems and methods for damping blade vibrations when the wind turbine rotor is in a shutdown state and configured with a turbinemounted crane that is operated via cables that extend to a ground location.BACKGROUND

[0002] Modem wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally include a tower and a rotor arranged on the tower. The rotor, which typically includes a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades, wherein the rotation generates a torque that is transmitted through a rotor shaft to a generator, either directly ("‘direct drive’7) or through the use of a gearbox. This way. the generator produces electricity which can be supplied to the electrical grid.

[0003] There is a trend to make wind turbine blades increasingly longer to capture more wind and convert the energy of the wind into electricity. This results in the blades being more flexible and more prone to aero-elastic instabilities, e.g.. vibrations of the blades that can also lead to unstable blade oscillations. Vibrating blades create the risk of major potential damage to the blades and other various components in the wind turbine.

[0004] When the wind turbine is in operation, a wind turbine controller may operate directly or indirectly an auxiliary drive system such as a pitch system or a yaw system to reduce loads on the blades. Similarly, vibrations of the blades may be counteracted. When the wind turbine is in a stand-still condition with the rotor either idling or locked, the risk of aero-elastic instabilities can occur.

[0005] Two types of vibrations that are of particular concern during stand-still conditions of the rotor are vortex induced vibrations (VIV) and stall induced vibrations (SIV). Vortex induced vibrations (VIV) tend to be induced at certain angles of attack of the blades and may or may not include cross flow vortices shed at700769-WO-1 / GECW-1264-PCT frequencies close to blade eigen frequencies or system frequencies. Stall-induced vibration (SIV) occur when the angle of attack is close to stall angles and the flow interaction leads to blade vibrations. The blade angle of attack is understood as a geometrical angle between the flow direction of the wind and the chord of the blade.

[0006] The vortex (VIV) and stall (SIV) induced vibrations are phenomena that are difficult or computationally expensive to simulate accurately with state of the art tools, so they may be inadequately considered in the design phase. This can lead, however, to extreme or accelerated fatigue blade and blade bolt failure. When all the blades are vibrating in phase (resonance), there is a potential risk of major turbine failure. The resonance, even if it lasts only a short time and does not cause a major failure, can create loads that may affect the fatigue life of structural components. The effect of these loads may be challenging to estimate due to lack of field data (magnitude and duration of vibrations).

[0007] A particularly critical risk scenario is when the rotor hub is in a nonrotating state (i.e., locked or standstill state) for events such as a blade installation or uptower blade work, major uptower component exchange (e.g.. a gearbox exchange), any work with a ground-based or turbine-based crane, maintenance, and so forth, wherein the ability to yaw the rotor into the wind is limited or constrained to a reduced yaw angle sweep.

[0008] For example, use of a traditional ground-based crane for major component exchanges / maintenance, such as a gearbox or generator exchange / maintenance, may not be feasible for various reasons (including cost, logistics, wind turbine location, etc.). In this situation, a turbine-mounted crane may be mounted to the bedplate within the nacelle (or to a component mounted to the bedplate) and operated via cables that extend to ground-based equipment located at the base of the tower. Commercial examples of such cranes are available, for example, from LIFTRA™ (Denmark) as the LT1000 and LT1200 Liftra Self-Hoisting Crane.

[0009] With use of these cranes, however, there is risk for stall-induced and vortex-induced (SIV / VIV) vibrations because the turbine rotor is locked and is unable to yaw due to the cables attached between the crane and the ground-based equipment at the base of the tower - the cables prevent the rotor from turning relative to the tower. The repair activity can take a significant amount of time to perform and700769-WO-1 / GECW-1264-PCT increases the probability of wind conditions that produce SIV / VIV vibrations. With conventional practices and system configurations, it can take many hours to partially uninstall the turbine-mounted crane to a configuration where the rotor can be yawed into the wind with no restrictions. This procedure is time consuming and cost- prohibitive to do on a regular basis (e.g., nightly). However, the ability to do a rotor gearbox exchange with a turbine-mounted crane is still beneficial where conventional ground-based cranes are not readily available or are cost prohibitive.

[0010] The present disclosure provides an effective means to reduce or prevent vibrations or oscillations in the wind turbine blades when the wind turbine is in anon- operational mode and the ability to yaw the rotor into the wind is constrained by the cables of a turbine-mounted crane.BRIEF DESCRIPTION

[0011] 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.

[0012] The present disclosure encompasses a method for reducing vibrations in a blade mounted on a hub of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend between a turbine-mounted crane and ground-based equipment. The method includes determining a new yaw position for the rotor that will reduce actual or predicted vibrations in the blade. A wind turbine controller is in communication with a yaw system and a crane controller, wherein the method includes yawing the rotor from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground-based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.

[0013] In a particular embodiment, the wind turbine controller determines a length of the cables necessary for the payout to the new yaw position and communicates with the crane controller to pay out the determined length of cable during the yawing. The turbine controller may communicate a payout speed to the700769-WO-1 / GECW-1264-PCT crane controller so that the cables wrap around the tower in coordination with a yaw rate.

[0014] The method may include shutting down the yaw system in the event of certain conditions. For example, the wind turbine controller may shut down the yaw system upon one of: (a) detection that a determined length of cable has been or is about to be exceeded; (b) a loss of communication with the crane controller; or (c) detection that a cable tension threshold is exceeded.

[0015] Embodiments of the method may include sensing a tension in the cables, wherein the wind turbine controller communicates with the crane controller to pay out the cables so that a desired cable tension is maintained during yawing of the rotor to the new yaw position.

[0016] Other embodiments of the method may include defining a yaw sweep for the rotor relative to a longitudinal axis of the rotor aligned with wind direction. This yaw sweep may be divided into multiple vibration risk zones on either side of a novibration zone that is aligned with the longitudinal axis of the rotor, wherein the wind turbine controller determines the new yaw position to be at a different vibration risk zone within the yaw sweep than the initial yaw position. These embodiments may include determining a wind speed of the wind acting on the blade, wherein the wind turbine controller determines the different vibration risk zone based on the wind speed. In certain embodiments, the wind turbine controller selects the different vibration risk zone to be the no-vibration zone (i.e. , with the rotor pointed essentially into the wind).

[0017] The method may include use of a secondary cable storage system operably configured the ground-based equipment and the tower, such as a driven reel or other type of cable accumulator, wherein the cables are paid out or taken up from the secondary cable storage system during the yawing process.

[0018] The term “cables’’ is used herein generically to include one or more cables, lines, ropes, chains, etc.

[0019] In still other embodiments, the wind turbine controller may be configured to rely on detection of actual blade vibrations at the initial yaw position before initiating the yawing to the new yaw position, wherein the new yaw position is at predefined increment from the initial yaw position. Upon detection of vibrations in700769-WO-1 / GECW-1264-PCT the blade at the new yaw position, the wind turbine controller may issue another yaw command to the yaw system to yaw the rotor to a second new yaw position that is in an opposite direction relative to the initial yaw position or is in the same direction as the new yaw position.

[0020] The present disclosure also encompasses a method for yawing a rotor of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend between a turbine-mounted crane and ground-based equipment, wherein the rotor is yawed to the new position for essentially any reason. The method includes determining a new yaw position for the rotor; and with a yaw system and a wind turbine controller in communication with the yaw system and a crane controller, yawing the rotor from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground-based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.

[0021] In a particular embodiment, it may be desired to limit sway of the tower during up-tower maintenance or repair procedures, wherein the new yaw position is determined to reduce the degree of tower sway.

[0022] It may also be desired to determine the new yaw position that keeps the turbine in a safe state while the ground equipment (e.g., winch, storage reel, control equipment) is repositioned on the ground.

[0023] The present disclosure also encompasses a wind turbine configured for reducing vibrations and loads in one or more blades mounted on a hub of a rotor when the rotor is in a stand-still state and in a limited yaw capacity7state. The wind turbine includes: a rotor with a hub at a forward end thereof, the rotor hub mounted atop a tower; a plurality of blades mounted on the hub; a yaw system; a turbine-mounted crane, and one or more cables extending between the turbine-mounted crane and ground-based equipment (e.g., a ground-based control station) for the turbinemounted crane; and a wind turbine controller in communication with the yaw system and a crane controller at the ground-based control station. The wind turbine controller is configured to perform the following operations: determine a new yaw position for the rotor that will reduce actual or predicted vibrations in the blades; and issue a yaw command to the yaw system to yaw the rotor from an initial yaw position to the new700769-WO-1 / GECW-1264-PCT yaw position while simultaneously controlling payout of the cables from the ground- based equipment with the crane controller so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.

[0024] In a particular embodiment of the wind turbine, the wind turbine controller is configured to determine a length of the cables necessary' for the payout to the new yaw position and to communicate with the crane controller to pay out the determined length of cable during the yawing. The wind turbine controller may further communicate a payout speed to the crane controller so that the cables wrap around the tower with a constant cable tension or cable angle. In an alternate embodiment, the system may pay out the cables based simply on a sufficient tension being generated to unwind and pull the cables from a storage reel or other device without the need of a cable tension controller (e.g., the yawing is sufficient to overcome an inherent resistance of the storage reel or other device). This embodiment may include a safety switch that shuts dow n the yaw system in the event of excess tension in the cables.

[0025] Embodiments of the wind turbine may include a cable tension sensor in communication with the wind turbine controller, wherein the wind turbine controller is further configured to communicate with the crane controller so that a desired cable tension or cable angle is maintained during the cable payout when yawing to the new yaw position.

[0026] In still other embodiments, the wind turbine controller may be configured to define a yaw sweep for the rotor divided into multiple vibration risk zones on either side of a no-vibration zone that is aligned with a longitudinal axis of the rotor pointed into the wind, wherein the wind turbine controller determines the new' yaw position to be at a different vibration risk zone within the yaw sweep than the initial yaw position. In these embodiments, the wind turbine may include a wind speed sensor in communication with the w ind turbine controller, wherein the wind turbine controller is configured to determine the different vibration risk zone based on a speed of the wind acting on the blades.

[0027] Other embodiments of the wind turbine may include a vibration sensor configured to detect actual vibrations in the blades, wherein the wind turbine controller is in communication with the vibration sensor and is further configure to: monitor for actual vibrations in the blades with the rotor at the initial yaw position;700769-WO-1 / GECW-1264-PCT upon detection of vibrations in the blades, determine the new yaw position and issue a yaw command to the yaw system to yaw the rotor to the new yaw position; and at the new yaw position of the rotor, continue to monitor for actual vibrations in the blades. Upon detection of vibrations in the blades at the new yaw position, the wind turbine controller may be configured to issue another yaw command to the yaw system to yaw the rotor to a second new yaw position that is in an opposite direction relative to the initial yaw position or is in the same direction as the new yaw position.

[0028] Another embodiment of the wind turbine may include a secondary cable storage system operably configured with the ground-based equipment, wherein the cables are paid out or taken up from the secondary cable storage system.

[0029] The wind turbine controller may be configured in various embodiments to perform any combination of the functions discussed above with respect to the method embodiments.

[0030] 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

[0031] 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:

[0032] Fig. 1 illustrates a perspective view of a wind turbine configured with an uptower crane;

[0033] Fig. 2 is a cut-away view of an embodiment of a wind turbine nacelle;

[0034] Fig. 3 is a functional control block diagram of embodiments of a method and system in accordance with the present disclosure;

[0035] Fig. 4 is a diagram depicting aspects of the present method related to vibrations risk zones relative to different wind directions;

[0036] Figs. 5A-5C are operational views of a wind turbine yawing in accordance with method and systems of the present disclosure; and700769-WO-1 / GECW-1264-PCT

[0037] Fig. 6 is a flow chart of a method embodiments in accordance with aspects of the present disclosure.

[0038] 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

[0039] Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0040] Referring now to the drawings, Fig. 1 illustrates a perspective view of one 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 rotor hub 20 and at least one rotor blade 22 coupled to and extending outwardly from the rotor 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 to an electric generator 25 positioned within the nacelle 16 to permit electrical energy to be produced.

[0041] The wind turbine 10 may also include a wind turbine controller 24 centralized within the nacelle 16. However, in other embodiments, the controller 24 may be located within any other component of the wind turbine 10 or at a location700769-WO-1 / GECW-1264-PCT outside the wind turbine 10. Further, the controller 24 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. For example, the controller 24 may be in communication with individual pitch drive systems associated with each rotor blade 22 in order to pitch such blades about a respective pitch axis 28. As such, the controller 24 may include a computer or other suitable processing unit. Thus, the controller 24 may include suitable computer- readable instructions that, when implemented, configure the controller 24 to perform various different functions, such as receiving, transmitting and / or executing wind turbine control signals. Accordingly, the controller 24 may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences), de-rating or up-rating the wind turbine, and / or individual components of the wind turbine 10.

[0042] As used herein, the term “controller” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. The controller is also configured to compute advanced control algorithms and communicate to a variety of Ethernet or serial-based protocols (Modbus, OPC, CAN, etc.). Additionally, a memory device(s) configured with the controller may generally include memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and / or other suitable memory elements. Such memory device(s) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the controller to perform the various functions as described herein.

[0043] The present disclosure relates to situations wherein the wind turbine 10 is non-operational (e.g., not producing electrical power) and the rotor 18 (and thus the rotor hub 20) is either locked against rotation or is left to idle, for instance due to installation, commissioning, maintenance tasks, or any other reason. The controller 24 may remain communicatively coupled to at least the pitch drive system and the yaw system (described below) in the locked or idling state of the rotor 18.700769-WO-1 / GECW-1264-PCTAlternatively, the “controller” function may also be provided by a separate dedicated controller during the locked or idling state of the rotor. This dedicated controller may be configured to operate autonomously, i.e.. independently from the wind turbine controller 24, at least in some operating conditions, and may be able to perform tasks such as receiving and emitting signals and processing data when the wind turbine controller 24 is otherwise unavailable.

[0044] The wind turbine 10 of Fig. 1 may be placed in an offshore or onshore location.

[0045] The nacelle 16 is rotatably coupled to the tower 12 through a yaw system 26 in such a way that the nacelle 16 is able to rotate about a rotating axis or “yaw axis”. The yaw system 26 includes a yaw bearing having two bearing components configured to rotate with respect to the other. The tower 12 is coupled to one of the bearing components and a bedplate or support frame of the nacelle 16 is coupled to the other bearing component. The yaw system 26 includes an annular gear 30 and a plurality of yaw drives 32 each having a motor 34, a gearbox 36, a shaft 23, and a pinion 38 that meshes with the annular gear 30 for rotating one of the bearing components with respect to the other.

[0046] Fig. 3 depicts a control diagram with the various inputs and considerations for the controller 24 discussed herein. For example, aspects of the present disclosure rely on sensors to detect various parameters, wherein the sensors are in communication with the controller 24. These sensors (collectively identified as components 40 in the figures) may include sensors configured to measure displacements, yaw, pitch, moments, strain, stress, twist, damage, failure, rotor torque, rotor speed, cable length, cable tension, a grid anomaly in the power grid, and / or an anomaly of power supplied to any component of wind turbine 10. Although exemplary sensors 40 are illustrated herein as coupled to various components of wind turbine 10, for example tower 12, blades 22, and hub 20, the sensors are not limited to attachment with such components, nor the location shown on such components.Rather, the sensor(s) 40 may be coupled to any component of wind turbine 10 and / or the power grid at any location thereof for measuring any parameter thereof, whether such component, location, and / or parameter is described and / or illustrated herein.700769-WO-1 / GECW-1264-PCT

[0047] As discussed, aspects of the present disclosure rely on detecting actual vibrations in the blades or other components of the wind turbine. These vibrations or oscillations may be detected or measured directly by displacement sensors 40 (e.g.. accelerometers or strain gauges) configured on the blades 22, as depicted in Fig. 1, or on other components that are indicative of blade vibrations, such as the tower, main shaft, gearbox, rotor lock, foundation or bedplate, and so forth. A vibration may be determined when the strain or deformation parameter satisfies a strain or deformation threshold, which may be determined by the controller 24.

[0048] Alternatively, the oscillations or vibrations may be predicted or modeled based on data from the sensors 40 disposed on the wind turbine to measure the wind parameters or sensors 40 disposed to detect the yaw position of the rotor hub. etc.

[0049] Aspects of the present disclosure may rely on detection of wind parameters of incident wind acting on the rotor 18, such as wind direction, wind speed, turbulence, and so forth. Referring to Fig. 2, the wind turbine 10 may include one or more wind parameter sensors 40 for measuring various wind parameters at the turbine, upwind of the turbine, or downwind from the wind turbine 10. For example, as shown in Fig. 2, one sensor 40 may be located on the hub 20 or nacelle 16 so as to measure an actual wind parameter upwind from the wind turbine 10. The actual wind parameter may be any of the following: a wind gust, a wind speed, a wind direction, a wind acceleration, a wind turbulence, a wind shear, a wind veer, a wake, or similar. Further, the one or more sensors 40 may include at least one LIDAR sensor for measuring upwind parameters. For example, the wind sensor 40 may be a LIDAR sensor, which is a measurement radar configured to scan an annular region around the wind turbine 10 and measure wind speed based upon reflection and / or scattering of light transmitted by the LIDAR sensor from aerosol. The cone angle (0) and the range (R) of the LIDAR sensor may be suitably selected to provide a desired accuracy of measurement as well as an acceptable sensitivity.

[0050] In further embodiments as depicted in Fig. 2, the one or more LIDAR sensors may also be located on the wind turbine tower 12. on one or more of the wind turbine blades, on the nacelle 16, on a meteorological mast of the wind turbine, or at any other suitable location. In still further embodiments, the wind parameter sensor 40 may be located in any suitable location near the wind turbine 10.700769-WO-1 / GECW-1264-PCT

[0051] In alternative embodiments, the sensors 40 need not be LIDAR sensors and may be any other suitable sensors capable of measuring wind parameters upwind of the wind turbine 10. For example, the sensors may be accelerometers, pressure sensors, angle of attack sensors, vibration sensors, MIMU sensors, camera systems, fiber optic systems, anemometers, wind vanes, Sonic Detection and Ranging (SOD AR) sensors, infra lasers, radiometers, pitot tubes, rawinsondes, other optical sensors, and / or any other suitable sensors. It should be appreciated that, as used herein with respect to the sensors, the term “determine” and variations thereof indicates that the various sensors of the wind turbine may be configured to provide a direct measurement of the parameters being monitored or an indirect measurement of such parameters. Thus, the sensors 40 may, for example, be used to generate signals relating to the parameter being monitored, which can then be utilized by the controller 24 to determine the actual wind condition.

[0052] When the rotor 18 / hub 20 are locked from rotating / yawing during a maintenance procedure, shutdown, or for any other reason, components of the wind turbine may be subjected to excessive loads. Excessive torque induced in the rotor 18 can result in very high and damaging loads in many components in the wind turbine, such the blades 22, hub 20, an interconnection between the tower 12 and the wind generator 12, a bedplate (not shown) of the tower 12, a foundation (not shown) of wind turbine 10, and drivetrain components including the gearbox and bearings. An aspect of the present disclosure may include consideration of one or more turbine component loads at the new yaw7position before issuing the yaw command to the new yaw position. In a particular embodiment, the load of interest is rotor torque load induced in the rotor at the new yaw position. Fig. 3 depicts one or more rotor torque sensors 40 that provide input to the controller 24. As discussed in greater detail below, aspects of the present disclosure may also relate to determining the new7yaw position that also reduces or optimizes mechanical rotor torque loads.

[0053] In an embodiment wherein several different types / component loads are considered, the process may include determining a yaw position that optimizes the various types of loads across the various components.

[0054] The loads in various components induced by the excessive rotor torque can be measured directly via sensors 40 (e g., accelerometers, strain gauges, or any other700769-WO-1 / GECW-1264-PCT ty pe of sensor as discussed above) located directly on the components. Alternatively, the loads may be predicted or modeled based on inputs such as such as wind speed, wind direction, rotor position, pitch angle, wind turbulence intensity, wind upflow, air density, temperature, wind sheer, and wind veer.

[0055] Referring to Fig. 4, characteristics of a representative wind turbine are depicted for SIV and VIV conditions for different relative wind directions and wind speeds. It should be appreciated that the values shown in Fig. 4 are for non-limiting, illustrative purposes only. These characteristics may vary’ between different types / designs of wind turbines, and the present invention is intended to encompass such variations.

[0056] In Fig. 4, a complete 360-degree yaw sweep of the rotor is divided into different SIV / VIV / No-Risk zones for a particular wind turbine configuration. For example, a forward “no risk” zone may be defined between + / - 20° relative to the longitudinal axis of the rotor (dashed line). When the rotor is yawed into the wind (i.e., pointed into the wind) within + / - 20, the likelihood of SI V / VIV vibrations being induced in the blades (or other turbine structure) is minimal. It should be appreciated that the wind speeds and angular values depicted in Fig. 4 and described herein are meant as an example only. These values may vary’ between different wind turbines and w ind turbine designs. Other safe zones may be possible depending on the turbine design (e.g., in between SIV and VIV zones). An angular SIV or VIV zone may also include a buffer zone at one or both sides of the zone.

[0057] Still referring to Fig. 4, SIV zones are depicted between [- 20° to -50°] and between [+20° to +50°] relative to the longitudinal axis 50 of the rotor aligned with wind direction. Additional SIV zones are depicted between [- 130° to -160°] and between [+130° to +160°] relative to the longitudinal axis 50 of the rotor aligned with the wind direction. SIV conditions are possible when the rotor is yawed to a position such that the wind direction lies within one of these SIV zones and wind speeds are greater than 12 m / s.

[0058] In Fig. 4, VIV zones are depicted between [-50° to -130°] and between [+50° to +130°] relative to the longitudinal axis 50 of the rotor aligned with the wind direction. VIV conditions are possible w’hen the rotor is yawed to a position such that700769-WO-1 / GECW-1264-PCT the wind direction lies within one of these VIV zones and wind speeds are between 9- 12 m / s.

[0059] It is generally understood that, in addition to wind direction. SIV and VIV conditions are more likely to be induced at certain wind speeds / ranges. Embodiments of the present method may also include control considerations that are dependent on wind speed. The diagram in Fig. 4 presents a critical wind speed of >12 m / s for SIV in the blades for illustrative purposes only. At wind speeds less than 12 m / s, SIV in the blades is not likely. Similarly, the critical wind speed range of 9-12 m / s is presented for VIV in the blades At w ind speeds outside of this range, VIV in the blades is not likely.

[0060] Fig. 1 depicts a fixed rotor gearbox exchange (FRGE) using a turbine mounted crane 42 (such as the LT1000 or LT1200 Liftra Self-Hoisting Crane) that is controlled by lines or cables 44 that extend down to ground-based equipment 46 that may be configured in a vehicle or other structure at the base of the tower 12. This type of system and procedure are known and used in the industry and need not be described in detail herein. With conventional methods, the cables 44 limit the yaw sweep of the rotor (e g., to a yaw sweep + / -750to 135°) and, even if the yaw system was operational, may prevent yawing of the rotor hub into the wind in the event that wind direction changes.

[0061] Aspects of the present method and systems are depicted in Figs. 5A-5C, which depict the cables 40 extending between the tower-mounted crane 42 and the ground-based equipment 46, which may include a controller 52 that is in communication with the wind turbine controller 24. The controller 52 may operate a winch or similar device at the control station 46 to pay out or take up the cables 44 as the hub 20 is yawed to a new7position, as depicted in Fig. 5B wherein the hub 20 has been yawed a complete 360-degree sweep as compared to the initial yaw position of Fig. 5A. A cable tension sensor 50 may be configured to detect tension in the cables 44 during the yawing process. The cables 44 may be wrapped with a constant tension and / or a constant wrap angle 54 relative to the longitudinal axis 55 of the tower 12. Various types of cable tension sensors or meters are known and commercially available for this purpose.700769-WO-1 / GECW-1264-PCT

[0062] Fig. 5C depicts a method and system embodiment wherein the ground- based equipment 46 includes a secondary storage system 56 operationally configured between the controller 52 and associated equipment and the tower 12. This system 56 may use a reel 57, drum, or other type of cable accumulator that accommodates the payout or take-up of the cables 44 at a constant tension. The reel 57 may have a plurality of wraps of the cables 44 and be driven (e.g.. via a motor, hydraulic system, rotational torque spring, etc.) in a first direction to pay out the cables 44 or in a second opposite direction to take up the cables 44 during the yawing process. The system 56 may include a controller 58 that is in communication with a cable tension sensor 50 and the ground-based equipment controller 52 and / or the wind turbine controller 24 so that the payout and take-up of the cables 44 is controlled to maintain the cables at a desired tension during the yawing process.

[0063] As mentioned above, the present disclosure also encompasses a method for yawing a rotor of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend between a turbine-mounted crane and ground-based equipment, wherein the rotor is yawed to the new position for essentially any reason. The method includes determining a new yaw position for the rotor; and with a yaw system and a wind turbine controller in communication with the yaw system and a crane controller, yawing the rotor from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground-based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position. For example, it may be desired to limit sway of the tower during up-tower maintenance or repair procedures, wherein the new yaw position is determined to reduce the degree of tower sway. In another embodiment, it may be desired to determine the new yaw position that keeps the turbine in a safe state while the ground equipment (e.g., winch, storage reel, control equipment) is repositioned on the ground.

[0064] Fig. 6 is an operational flow chart depicting various method embodiments 100 in accordance with aspects of the disclosure discussed above related to the embodiments intended to reduce vibrations in a blade mounted on a hub of a wind turbine rotor when the rotor is in a stand-still and a limited yaw capacity state because700769-WO-1 / GECW-1264-PCT of cables that are rigged between maintenance equipment in / on the rotor (e.g., a turbine-mounted crane) and ground-based equipment. The method may be conducted for a single wind turbine blade or multiple (e.g.. all) wind turbine blades configured on the hub.

[0065] At step 102, the method monitors for actual blade vibrations using one or more suitable vibration sensors (step 104). such as one of the sensors 40 in Figs. 1 and 3 discussed above, to directly sense the vibrations or parameter indicative of vibrations induced in the blades. Alternatively, the method may rely on a prediction or assumption of blade vibrations based on wind parameters sensed with one or more of the wind sensors 40 (step 106) discussed above and the rotational position of the rotor relative to the wind (step 108) determined by a suitable rotor position sensor.Vibrations may be determined based on the risk zones discussed above with respect to Fig. 4 and the actual w ind speed and wind direction relative to the yaw position of the rotor.

[0066] Step 110 indicates that actual vibrations have been detected or predicted / assumed. wherein the process proceeds to step 112 and the wind turbine controller determines a new yaw position to reduce the actual vibrations or the likelihood of vibrations. This new yaw position may be determined in various ways. For example, referring to Fig. 4 above and related discussion, the new- yaw position may be determined based on risk zones (step 114) and wind speed (step 115).Relative to a longitudinal axis of the rotor aligned with wind direction, the yaw sweep may be divided into multiple vibration risk zones on either side of a no-vibration zone that is aligned with the longitudinal axis of the rotor (with the rotor pointed into the wind). The controller may determine the new yaw position to be in a different vibration risk zone within the allowable yaw sweep than the initial yaw position based on the wind speed.

[0067] In another embodiment, at step 112 the new yaw position is determined based on a predefined increment from the initial yaw position. For example, the new yaw position may be a predefined increment of, e.g., + / - 5 degrees relative to the initial yaw position from the initial yaw position. Subsequent incremental yaw positions may be determined if vibrations are detected in the blades at the first new7position. For example, the second new' yaw position may be at the same increment700769-WO-1 / GECW-1264-PCT and direction as the first new yaw position. Alternately, the second yaw position may be in an opposite direction relative to the initial yaw position and / or at a different yaw increment.

[0068] Blocks 116 and 118 in Fig. 5 indicate that additional considerations may be used to determine the new yaw positions. For example, step 116 relates to sensing wind speed and determining if a critical wind speed is exceeded. As discussed above with respect to Fig. 4, an exemplary critical wind speed of >12 m / s is defined for SIV in the blades. At wind speeds less than 12 m / s, SIV in the blades is not likely. Similarly, the critical wind speed range of 9-12 m / s is presented for VIV in the blades At wind speeds outside of this range, VIV in the blades is not likely. If the detected wind speed does not exceed a critical wind speed (regardless of the risk zone in which the initial yaw position lies), anew yaw position may not be necessary / determined at step 112.

[0069] Similarly, step 118 includes consideration of one or more turbine component loads at the new yaw position before issuing the yaw command to the new yaw position, such as blade loads, tower loads, and so forth. In a particular embodiment, the load of concern is torque load induced in the rotor at the new yaw position based on the existing wind conditions. Alternatively, a plurality of rotor torque loads for different wind conditions may be predetermined and stored for access by the controller. The rotor torque load is compared to a threshold value and if the rotor torque load does not exceed the threshold value, then the process proceeds to issuing the yaw command for the new yaw positions. If the rotor torque load exceeds the threshold value at step 118, then another yaw position may be determined. The process will repeat until a new yaw position is determined that results in rotor torque not exceeding the threshold value.

[0070] In an embodiment wherein several different types / component loads are considered, the process may include determining a yaw position that optimizes the loads across the various components.

[0071] Step 120 indicates that a shutdown condition may be monitored for and, if satisfied at step 122, the yaw system may be shutdown at step 124. Specifically, the shutdow n condition may require that communications between the wind turbine700769-WO-1 / GECW-1264-PCT controller / ground-based station controller / storage system controller are established and verified or the yaw system is shutdown.

[0072] If the communications are verified at step 126. then the process proceeds to yawing the rotor to the new yaw position at step 128 wherein the wind turbine controller issues a yaw command to the yaw system controller at step 134 to yaw the rotor while simultaneously communicating with the ground-based system controller at step 136 (and, if utilized, the storage system controller at step 138) to control the payout or take-up of the cables during yawing of the rotor.

[0073] Steps 130, 132, and 133 relate to considerations that may be used during the yawing process. For example, step 130 relates to maintaining a desired cable tension (as sensed by a sensor and discussed above) on the cables during yawing of the rotor by coordinating the cable payout speed (determined at step 133) with rotor yaw rate. This process may also be used to achieve a desired constant cable angle (Fig. 5B). The cable payout speed and cable tension values may also be considered for shutdown conditions. If the actual cable tension or cable payout speed exceeds a respective threshold value, then the yaw system may be shut down at steps 135 / 124.

[0074] Step 132 relates to determining the length of the cable to be paid out from the ground-based equipment to achieve the new yaw position, and measuring the length of cable being paid out during the yawing process (e.g., with an encoder or similar device). The cable length may be used as a control variable to, e.g., determine a run time for a winch in the ground-based equipment and / or a shutdown condition variable. If the actual length of cable being paid out exceeds the predicted cable length, then the yaw system may be shut down at steps 135 / 124.

[0075] Further aspects of the invention are provided by the subject matter of the following clauses:700769-WO-1 / GECW-1264-PCTClause 1 : A method for reducing vibrations in a blade mounted on a hub of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend between a turbine-mounted crane and ground-based equipment, the method comprising: determining a new yaw position for the rotor that will reduce actual or predicted vibrations in the blade; and with a yaw system and a wind turbine controller in communication with the yaw system and a crane controller, yawing the rotor from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground- based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.Clause 2: The method according to clause 1, wherein the wind turbine controller determines a length of the cables necessary for the payout to the new yaw position and communicates with the crane controller to payout the determined length of cable during the yawing.Clause 3: The method according to any preceding clause, wherein the turbine controller further communicates a payout speed to the crane controller so that the cables wrap around the tower in coordination with a yaw rate.Clause 4: The method according to any preceding clause, wherein the wind turbine controller shuts down the yaw sy stem upon one of: (a) detection that a determined length of cable has been or is about to be exceeded; (b) a loss of communication with the crane controller; or (c) detection that a cable tension threshold is exceeded.Clause 5: The method according to any preceding clause, further comprising sensing a tension in the cables, wherein the wind turbine controller communicates with the crane controller so that a desired cable tension is maintained during the cable payout when yawing to the new yaw- position.Clause 6: The method according to any preceding clause, wherein, relative to a longitudinal axis of the rotor aligned w-ith wind direction, a yaw sweep for the rotor is divided into multiple vibration risk zones on either side of a no-vibration zone that is aligned with the longitudinal axis of the rotor, wherein the wind turbine controller determines the new yaw position to be at a different vibration risk zone within the yaw sweep than the initial yaw position.700769-WO-1 / GECW-1264-PCTClause 7: The method according to any preceding clause, further comprising determining a wind speed of the wind acting on the blade, wherein the wind turbine controller determines the different vibration risk zone based on the wind speed.Clause 8: The method according to any preceding clause, wherein the wind turbine controller relies on detection of actual blade vibrations at the initial yaw position before initiating the yawing to the new yaw position, wherein the new yaw position is at a predefined increment from the initial yaw position.Clause 9: The method according to any preceding clause, wherein upon detection of vibrations in the blade at the new yaw position, the wind turbine controller issues a yaw command to the yaw system to yaw the rotor to a second new yaw position that is in an opposite direction relative to the initial yaw position or is in the same direction as the new yaw position.Clause 10: The method according to any preceding clause, wherein the ground-based equipment includes a secondary cable storage system, the method further comprising paying out or taking up the cables from the secondary cable storage system.Clause 11 : A method for yawing a rotor of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend between a turbine-mounted crane and ground-based equipment, the method comprising: determining a new yaw position for the rotor; and wi th a yaw system and a wind turbine controller in communication with the yaw system and a crane controller, yawing the rotor from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground- based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.Clause 12: The method according to clause 11, wherein the new yaw position is determined based on reducing sway of the tower.Clause 13: A wind turbine configured for reducing vibrations and loads in blades mounted on a hub of a rotor when the rotor is in a stand-still state and in a limited yaw capacity state, the wind turbine comprising: a rotor with a hub at a forward end thereof, the rotor hub mounted atop a tower; a plurality- of blades mounted on the hub; a yaw system; a turbine-mounted crane, and one or more cables700769-WO-1 / GECW-1264-PCT extending between the turbine-mounted crane and ground-based equipment for the turbine-mounted crane; a wind turbine controller in communication with the yaw system and a crane controller, the wind turbine controller configured to perform the following operations: determine a new- yaw position for the rotor that will reduce actual or predicted vibrations in the blades; and issue a yaw command to the yaw system to yaw the rotor from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground-based equipment with the crane controller so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw7position.Clause 14: The wind turbine according to clause 3, wherein the wind turbine controller is configured to determine a length of the cables necessary for the cable payout to the new yaw position and to communicate with the crane controller to pay out the determined length of cable during the yawing.Clause 15: The wind turbine according to any preceding clause, wherein the wind turbine controller further communicates a payout speed to the crane controller so that the cables wrap around the tower with a constant cable tension or cable angle.Clause 16: The wind turbine according to any preceding clause, further comprising a cable tension sensor in communication with the wind turbine controller, wherein the wind turbine controller is further configured to communicate with the crane controller so that a desired cable tension is maintained during the payout when yawing to the new yaw- position.Clause 17: The wind turbine according to any preceding clause, wherein the wind turbine controller is configured to define a yaw sweep for the rotor divided into multiple vibration risk zones on either side of a no-vibration zone that is aligned with a longitudinal axis of the rotor pointed into the wind, wherein the wind turbine controller determines the new yaw position to be at a different vibration risk zone within the yaw7sweep than the initial yaw7position, and further comprising a wind speed sensor in communication with the wind turbine controller, wherein the controller determines the different vibration risk zone based on a speed of the wind acting on the blades.700769-WO-1 / GECW-1264-PCTClause 18: The wind turbine according to any preceding clause, wherein the ground-based equipment further comprises a secondary cable storage system, wherein the cables are paid out or taken up from the secondary cable storage system.Clause 19: The wind turbine according to any preceding clause, further comprising a vibration sensor configured to detect actual vibrations in the blades, the wind turbine controller in communication with the vibration sensor and further configured to: monitor for actual vibrations in the blades with the rotor at the initial yaw position; upon detection of vibrations in the blades, determine the new yaw position and issue a yaw command to the yaw system to yaw the rotor to the new yaw position; and at the new yaw position of the rotor, continue to monitor for actual vibrations in the blades.Clause 20: The wind turbine according to any preceding clause, wherein upon detection of vibrations in the blades at the new yaw position, the wind turbine controller is configured to issue another yaw command to the yaw system to yaw the rotor to a second new yaw position that is in an opposite direction relative to the initial yaw position or is in the same direction as the new yaw position.

[0076] 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

700769-WO-1 / GECW-1264-PCTWHAT IS CLAIMED IS:

1. A method for reducing vibrations in a blade mounted on a hub of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend between a turbine-mounted crane and ground-based equipment, the method comprising: determining a new yaw position for the rotor that will reduce actual or predicted vibrations in the blade: and with a yaw system and a wind turbine controller in communication with the yaw system and a crane controller, yawing the rotor from an initial yaw position to the new' yaw position while simultaneously controlling payout of the cables from the ground-based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.

2. The method according to claim 1, w herein the wind turbine controller determines a length of the cables necessary for the payout to the new yaw position and communicates with the crane controller to payout the determined length of cable during the yawing.

3. The method according to claim 2, w herein the wind turbine controller communicates a payout speed to the crane controller so that the cables wrap around the tower in coordination with a yaw rate.

4. The method according to claim 1 , w herein the wind turbine controller shuts down the yaw system upon one of: (a) detection that a determined length of cable has been or is about to be exceeded; (b) a loss of communication with the crane controller; or (c) detection that a cable tension threshold is exceeded.

5. The method according to claim 1. further comprising sensing a tension in the cables, wherein the wind turbine controller communicates with the crane controller so that a desired cable tension is maintained during the cable payout when yawing to the new yaw position.700769-WO-1 / GECW-1264-PCT6. The method of claim 1, wherein, relative to a longitudinal axis of the rotor aligned with wind direction, a yaw sweep for the rotor is divided into multiple vibration risk zones on either side of a no-vibration zone that is aligned with the longitudinal axis of the rotor, wherein the wind turbine controller determines the new yaw position to be at a different vibration risk zone within the yaw sweep than the initial yaw position.

7. The method of claim 6, further comprising determining a wind speed of the wind acting on the blade, wherein the wind turbine controller determines the different vibration risk zone based on the wind speed.

8. The method of claim 1, wherein the wind turbine controller relies on detection of actual blade vibrations at the initial yaw position before initiating the yawing to the new yaw position, wherein the new yaw position is at a predefined increment from the initial yaw position.

9. The method of claim 8, wherein upon detection of vibrations in the blade at the new yaw position, the wind turbine controller issues a yaw command to the yaw system to yaw the rotor to a second new yaw position that is in an opposite direction relative to the initial yaw position or is in the same direction as the new yaw position.

10. The method of claim 1, wherein the ground-based equipment includes a secondary' cable storage system, the method further comprising paying out or taking up the cables from the secondary cable storage system.

11. A method for yawing a rotor of a wind turbine rotor mounted atop a tower when the rotor is in a stand-still and limited yaw capacity state due to one or more cables that extend betw een a turbine-mounted crane and ground-based equipment, the method comprising: determining a new yaw- position for the rotor; and with a yaw system and a wind turbine controller in communication with the yaw system and a crane controller, yawing the rotor from an initial yaw position to the700769-WO-1 / GECW-1264-PCT new yaw position while simultaneously controlling payout of the cables from the ground-based equipment so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.

12. The method of claim 11, wherein the new7yaw7position is determined based on reducing sw ay of the tower.

13. A wind turbine configured for reducing vibrations and loads in blades mounted on a hub of a rotor when the rotor is in a stand-still state and in a limited yaw7capacity state, the wind turbine comprising: a rotor with a hub at a forward end thereof, the rotor hub mounted atop a tower; a plurality of blades mounted on the hub; a yaw system; a turbine-mounted crane, and one or more cables extending between the turbine-mounted crane and ground-based equipment for the turbine-mounted crane; a wind turbine controller in communication with the yaw system and a crane controller, the wind turbine controller configured to perform the following operations: determine a new7yaw position for the rotor that will reduce actual or predicted vibrations in the blades; and issue a yaw command to the yaw system to yaw the rotor from an initial yaw position to the new yaw position while simultaneously controlling payout of the cables from the ground-based equipment with the crane controller so that the cables wrap at least partially around the tower as the rotor rotates relative to the tower to the new yaw position.

14. The w ind turbine according to claim 13, wherein the wind turbine controller is configured to determine a length of the cables necessary for the cable payout to the new yaw position and to communicate with the crane controller to pay out the determined length of cable during the yawing.700769-WO-1 / GECW-1264-PCT15. The wind turbine according to claim 14, wherein the wind turbine controller further communicates a payout speed to the crane controller so that the cables wrap around the tower with a constant cable tension or cable angle.

16. The wind turbine according to claim 13, further comprising a cable tension sensor in communication with the wind turbine controller, wherein the wind turbine controller is further configured to communicate with the crane controller so that a desired cable tension is maintained during the payout when yawing to the new yaw position.

17. The wind turbine according to claim 13. wherein the wind turbine controller is configured to define a yaw sweep for the rotor divided into multiple vibration risk zones on either side of a no-vibration zone that is aligned with a longitudinal axis of the rotor pointed into the wind, wherein the wind turbine controller determines the new yaw position to be at a different vibration risk zone within the yaw sweep than the initial yaw position, and further comprising a wind speed sensor in communication with the wind turbine controller, wherein the controller determines the different vibration risk zone based on a speed of the wind acting on the blades.

18. The wind turbine according to claim 13, wherein the ground-based equipment further comprises a secondary cable storage system, wherein the cables are paid out or taken up from the secondary cable storage system.

19. The wind turbine according to claim 13. further comprising a vibration sensor configured to detect actual vibrations in the blades, the wind turbine controller in communication with the vibration sensor and further configured to: monitor for actual vibrations in the blades with the rotor at the initial yaw position; upon detection of vibrations in the blades, determine the new yaw position and issue a yaw command to the yaw system to yaw the rotor to the new yaw position; and700769-WO-1 / GECW-1264-PCT at the new yaw position of the rotor, continue to monitor for actual vibrations in the blades.

20. The wind turbine according to claim 19, wherein upon detection of vibrations in the blades at the new7yaw7position, the wind turbine controller is configured to issue another yaw command to the yaw system to yaw the rotor to a second new yaw position that is in an opposite direction relative to the initial yaw position or is in the same direction as the new yaw position.

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