System and method for continuous yawing of a wind turbine within a constrained YAW angle sweep upon detection of blade vibrations

Abstract

A system and method reduce vibrations in a blade mounted on a hub of a wind turbine rotor when the rotor is in a limited yaw capacity state with a defined allowable yaw sweep. An allowable yaw sweep is defined for the limited yaw capacity state. A sensor in communication with a controller monitors for vibrations in the blade with the rotor at an initial yaw position. Upon detection of vibrations, the controller determines a yaw sweep sector that is within and less than the allowable yaw sweep and issues a command to a yaw system to yaw the rotor in a continuous back and forth manner in the yaw sweep sector. The controller continues to monitor for vibrations in the blade during or after the continuous yawing of the rotor and stops the continuous yawing of the rotor when the blade vibrations reduce to below the threshold level.

Description

701178-WO-1 / GECW-1281-PCTSYSTEM AND METHOD FOR CONTINUOUS YAWING OF A WIND TURBINE WITHIN A CONSTRAINED YAW ANGLE SWEEP UPON DETECTION OF BLADE VIBRATIONSFIELD

[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 limited yawing state.BACKGROUND

[0002] Modem wind turbines are commonly used to supply electncity 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”) 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 flow7vortices shed at frequencies close to blade eigen frequencies or system frequencies. Stall-induced701178-WO-1 / GECW-1281-PCT vibration (SIV) occur when the angle of attack is close to stall angles and the flow interaction leads to blade vibrations.

[0006] The vortex (V1V) 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, and the ability to yaw the rotor into the wind is limited or constrained to a reduced yaw angle sweep.

[0008] For example, during a fixed rotor gearbox exchange (FRGE) using a turbine mounted crane, there is risk for stall-induced and vortex-induced (SIV / VI V) vibrations because the turbine rotor is locked, and the turbine is unable to yaw due to the cables attached between the crane and the control equipment at the base of the tower. This repair activity can take a significant amount of time to perform and 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). The ability to do a FRGE with a turbine-mounted crane is beneficial where conventional base cranes are not readily available or are cost prohibitive. Commercial examples of such cranes are available, for example, from LIFTRA™ (Denmark) as the LT1000 and LT1200 Liftra SelfHoisting Crane.701178-WO-1 / GECW-1281-PCT

[0009] 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.BRIEF 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] The present disclosure encompasses a method for reducing vibrations in a blade mounted on a hub of a wind turbine rotor when the rotor is in a stand-still state with limited yaw capacity. The method includes defining an allowable yaw sweep for the limited yaw capacity state. One or more sensors are in communication with a controller and are used to monitor (directly or indirectly) for actual vibrations in the blade with the rotor at an initial yaw position. Upon detection of vibrations in the blade exceeding a threshold level, the controller determines a yaw sweep sector that is within and less than the limits of the allowable yaw sweep. The controller issues a yaw command to a yaw system to yaw the rotor in a continuous back and forth manner in the yaw sweep sector. The method continues to monitor for vibrations in the blade during or after the continuous back and forth yawing of the rotor in the yaw sweep sector, wherein the continuous back and forth yawing of the rotor in the yaw sweep sector is stopped when the blade vibrations are reduced to below the threshold level.

[0012] In one embodiment, a mean position of the yaw sweep sector corresponds to the initial yaw position of the rotor. For example, the yaw sweep sector may be + / - 10° to either side of the initial 0° relative heading of the rotor for a total 20° sweep with a mean of 0° - meaning that the midpoint of the yaw sweep corresponds to the 0° relative heading of the rotor. In a different embodiment, the mean position of the yaw sweep sector is different than the initial yaw position of the rotor. For example, the yaw sweep sector may be +5° / -15° to either side of the initial 0° relative heading of the rotor for a total yaw sweep of 20° sweep with a mean at a -5° relative heading - meaning that the midpoint of the yaw sweep is at the -5° relative heading.701178-WO-1 / GECW-1281-PCT

[0013] In the event that the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the method includes changing the parameters of the yaw sweep sector within the allowable yaw sweep. For example, the range of the yaw sweep sector may be increased (e.g., from + / - 10° to + / - 20°) in a particular embodiment of the method. In a different embodiment, the controller may move the mean position (heading) of the yaw sweep sector. In still a further embodiment, the method may change a characteristic of the yawing motion of the rotor within the yaw sweep sector. For example, the rate of yawing may be increased, decreased, or varied throughout the yaw sweep sector. The continuous characteristic of the yawing may be changed to a continuous pulsing rate having a fixed or variable frequency. The method includes any one or combination of the changes to the yaw sweep sector or yaw motion characteristics. The controller may determine the changes to the yawing motion and / or range of the yaw sweep sector based on characteristics of the sensed blade vibrations.

[0014] The method may repeat with additional changes to the yaw sweep sector and / or yawing characteristics until the blade vibrations are reduced to below the threshold level.

[0015] After the blade vibrations have been reduced to below the threshold level, the method may include yawing the rotor to the initial yaw position prior to stopping the continuous yawing. In other words, the rotor may be parked at its initial rotor position.

[0016] The present disclosure also encompasses 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, limited yaw capacity state. The wind turbine includes the rotor and a plurality of the blades mounted on the hub, as well as a yaw system. One or more sensors are configured to directly or indirectly detect vibrations in one or more of the blades. A controller is in communication with the yaw system and the vibration sensors and is configured to perform the following operations: define an allowable yaw sweep for the limited yaw capacity state; monitor for vibrations in the blades with the rotor at an initial yaw position; upon detection of vibrations in the blade exceeding a threshold level, determine a yaw sweep sector that is within and less than701178-WO-1 / GECW-1281-PCT the allowable yaw sweep and issue a yaw command to the yaw system to yaw the rotor in a continuous back and forth manner in the yaw sweep sector; continue to monitor for vibrations in the blade during or after the continuous back and forth yawing of the rotor in the yaw sweep sector; and stop the continuous back and forth yaw ing of the rotor w hen the blade vibrations reduce to below' the threshold level.

[0017] The controller may be configured in various embodiments to perform any combination of the functions discussed above with respect to the method embodiments.

[0018] 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

[0019] 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, w'hich makes reference to the appended figures, in w'hich:

[0020] Fig. 1 illustrates a perspective view' of a wind turbine configured with an uptower crane;

[0021] Fig. 2 is a cut-away view of an embodiment of a wind turbine nacelle;

[0022] Fig. 3 is a functional control block diagram of embodiments of a method and system in accordance with the present disclosure;

[0023] Fig. 4 a diagram depicting aspects of the present method;

[0024] Figs. 5a through 5c are diagrams depicting an embodiment of continuous yawing of the rotor in response to a change in w ind conditions and detection of blade vibrations;

[0025] Figs. 6a through 6c are diagrams depicting another embodiment of continuous yawing of the rotor in response to a change in wind conditions and detection of blade vibrations; and

[0026] Fig. 7 is a flow chart of a method embodiments in accordance with aspects of the present disclosure.701178-WO-1 / GECW-1281-PCT

[0027] 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

[0028] 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.

[0029] 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.

[0030] The wind turbine 10 may also include a wind turbine controller 24 (Fig. 2) 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 location 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 control701178-WO-1 / GECW-1281-PCT 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.

[0031] 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 a yaw system (described below) in the locked or idling state of the rotor 18. Alternatively, 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 otherw ise unavailable.

[0032] The wind turbine 10 of Fig. 1 may be placed in an offshore or onshore location.

[0033] 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 “yawaxis”. The yaw system 26 includes a yaw7bearing having tw o 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 a701178-WO-1 / GECW-1281-PCT pinion 38 that meshes with the annular gear 30 for rotating one of the bearing components with respect to the other.

[0034] 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 40 / 48 may include sensors configured to measure displacements, yaw, pitch, moments, strain, stress, twist, damage, failure, rotor torque, rotor speed, a grid anomaly in the power grid, and / or an anomaly of power supplied to any component of wind turbine 10. Although exemplary7sensors 40 are illustrated herein as coupled to various components of wind turbine 10, for example tower 12, blades 22. and hub 20, the sensors 40 described herein are not limited to attachment with the components each sensor is shown as coupled to, 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 pow er grid at any location thereof for measuring any parameter thereof, whether such component, location, and / or parameter is described and / or illustrated herein.

[0035] As discussed, aspects of the present disclosure rely on detecting or determining actual vibrations in the blades or other components of the wind turbine. These vibrations or oscillations may be detected or measured directly by sensors 48 (e.g., accelerometers, strain gauges, vibrations sensors, MIMU sensors, camera or fiber optic systems, laser systems, optical sensors, or any other suitable sensor) configured on the blades 22, as depicted in Fig. 1. A vibration of a blade may be determined w hen the strain or deformation parameter satisfies a strain or deformation threshold, which may be determined by the controller 24.

[0036] Alternatively, the oscillations or vibrations may be predicted or inferred based on data from the sensors 40 disposed on the wind turbine to measure the wind parameters or sensors disposed to detect any other parameter of a component of the wind turbine that indicates that blade vibrations are likely or actually exist.

[0037] It should be appreciated that, as used herein with respect to the sensors, the terms “determine”, “detect”, and variations thereof , indicate 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.701178-WO-1 / GECW-1281-PCT

[0038] 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 upw ind of 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 sensor 40 in the hub 20 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 (9) and the range (R) of the LIDAR sensor maybe suitably selected to provide a desired accuracy of measurement as well as an acceptable sensitivity.

[0039] 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.

[0040] 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 signals701178-WO-1 / GECW-1281-PCT relating to the parameter being monitored, which can then be utilized by the controller 24 to determine the actual wind condition.

[0041] 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 memory7element(s) including, but not limited to, computer readable medium (e.g., random access memory7(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 memory7elements. Such memory7device(s) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 402, configure the controller to perform the various functions as described herein.

[0042] Referring to Fig. 4, characteristics of a representative wind turbine are depicted for SIV and VIV conditions for different relative wind directions and wind speed. 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.

[0043] In Fig. 4, a partial yaw arc of the rotor is divided into different SIV / VIV / No-Risk zones for a particular wind turbine configuration. A forward “no risk” zone is defined between + / - 20° relative to the longitudinal axis of the rotor (dashed line). This range could vary7depending on the turbine design. Other safe zones may be possible depending on the turbine design (e.g., in between SIV and VIV zones). When the rotor is yawed into the wind (i.e., pointed into the wind) within + / - 20, the likelihood of SIV / VIV vibrations being induced in the blades (or other turbine structure) is minimal.701178-WO-1 / GECW-1281-PCT

[0044] 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.

[0045] 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. 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. It should be appreciated that these wind speeds / ranges may vary depending on the turbine design.

[0046] When the rotor is able to complete a 360° yaw sweep (or opposite 180° sweeps relative), the conventional practice is to yaw the rotor to point the rotor hub 20 into the wind regardless of wind direction. However, as discussed above, certain conditions may dictate a limited yaw capacity state that inhibits the ability of the yaw system to encompass a complete 360° yaw sweep and prevents the rotor hub from being yawed directly into the wind.

[0047] For example, the limited yaw capacity state may be implemented during one of: a blade installation or up tower blade work, major up tower component exchange (e.g., a gearbox exchange), any work with a ground-based or turbine-based crane, maintenance, and so forth, and the ability to yaw the rotor into the wind is limited or constrained to a reduced yaw angle sweep. Fig. 1 depicts, for example, a fixed rotor gearbox exchange (FRGE) using a turbine mounted crane 42 that is controlled by lines or cables 44 that extend down to a vehicle 46 or other ground- based equipment or control station at the base of the tower 12. This type of procedure is known and practiced in the industry and need not be described in detail herein. The cables 44 limit the yaw sweep of the rotor 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.

[0048] The term “cables” is used herein generically to include one or more cables, lines, ropes, chains, etc.701178-WO-1 / GECW-1281-PCT

[0049] It may be necessary or desired to loosen or slack the cables 44 (without removing the cables from between the crane 42 and ground control station 46) to define a workable yaw sweep of the rotor.

[0050] Fig. 4 depicts an allowable yaw sweep of + / - 90 degrees relative to the initial yaw position (a total sweep of 180 degrees). This is for illustrative purposes only. The allowable yaw sweep may be greater or less than the depicted + / - 90 degrees.

[0051] Fig. 7 is a flow chart depicting various method embodiments 100 in accordance with aspects of the disclosure discussed above for reducing vibrations in a blade mounted on a hub of a wind turbine rotor when the rotor is in a stand-still state and a limited yaw capacity state. The method may be conducted for a single wind turbine blade or multiple (e.g., all) wind turbine blades configured on the hub. Fig. 7 will be discussed also with reference to the embodiments of the method depicted in Figs. 5a-5c and 6a-6c.

[0052] At step 102, the method includes defining the allowable yaw sweep of the rotor in the limited yaw capacity state of the rotor. As discussed above, the yaw sweep corresponds to an arc that is less than a complete 360-degree revolution of the rotor hub relative to an axis of the wind turbine tower. Figs. 5a and 6a depict an allowable yaw sweep of about + / -90 degrees for illustrative purposes only. In Fig. 5 a, the initial yaw position of the rotor (the 0 degree relative position of the rotor) is directly into the wind. In Fig. 6a, the initial yaw position of the rotor is offset by 25 degrees from the wind (the wind direction is at +25 degrees relative to the 0 degree yaw position of the rotor 20).

[0053] At step 104, the method includes continuously or periodically monitoring for blade vibrations induced by the wind. As discussed above, this monitoring may be performed by various sensors that directly or indirectly detect blade vibrations, the sensors in communication with a controller.

[0054] Fig. 5a indicates that the wind has changed direction to +20 degrees and has a speed of 14 m / s. Thus, the wind has moved into one of the SIV risk sectors (relative to the 0 degree relative heading of the rotor) and exceeds the SIV risk wind speed. SIV vibrations may be induced in the blades with this scenario. Similarly, Fig. 6a indicates that the wind has changed direction to +40 degrees and increased701178-WO-1 / GECW-1281-PCT speed of 16 m / s. Thus, the wind is in the SIV risk sector and now exceeds the SIV risk wind speed. SIV vibrations may be induced in the blades with this scenario.

[0055] At step 108, the method confirms that vibrations in one or more of the blades above a predetermined threshold have been detected.

[0056] At step 110, the controller determines a first yaw sweep sector (that is less than the allowable yaw sweep) and issues a command to the yaw system to commence continuous yawing of the rotor in the yaw sweep sector. For example, Figs. 5b and 6b depict that the rotor has commenced continuous back-and-forth yawing in a yaw sweep sector of 20° (+ / - 10°) having a mean of 0° (+ / - 10° on either side of the initial 0 degree relative yaw position of the rotor).

[0057] At step 110, the controller may conduct the continuous yawing for a predetermined time period, for example for 10 minutes. It should be appreciated that the “continuous” nature of the yawing includes a constant uninterrupted rate, a variable or changing uninterrupted rate, or a pulsed rate having a fixed or variable frequency.

[0058] Step 111 indicates a wait period (e.g., 1 minute) after the continuous yawing period of step 110. It may be that the blade vibrations ceased or decreased during the continuous yawing period, and this wait period may be provided to determine if the blade vibrations will start again or increase after the continuous yawing period has ceased. It may also be that the blade vibrations did not cease or decrease during the continuous yawing period of step 110, in which case the vibrations will still be present and detected after the wait period of step 111.

[0059] At step 112, the method may then recommence or continue monitoring for the blade vibrations after the prescribed wait period. At step 114, the method determines that the vibrations have ceased or been reduced below the threshold level and the method reverts to step 104.

[0060] If at step 116 the method determines that the blade vibrations did not stop or decrease below the threshold level (or started again). The method then proceeds to step 118 wherein the controller defines a second yaw sweep sector with characteristics that are different from the first yaw sweep sector. For example, as compared to the first yaw sweep sector, the second yaw sweep sector may have any one or combination of: (a) an increased or decreased yaw sweep sector within the allowable701178-WO-1 / GECW-1281-PCT yaw sweep; (b) a changed mean position of the yaw sweep sector; or (c) a different characteristic of the continuous yawing of the rotor in the yaw sweep sector (e.g., different rate, pulsed rate, constant rate, variable rate). In the embodiment of Fig. 5c, the yaw sweep sector has been modified to a yaw sweep sector of 30° (+ / - 15°) having a mean of 0° (+ / - 15° on either side of the initial 0 degree relative yaw position of the rotor). In the embodiment of Fig. 6c, the yaw sweep sector has been modified to a yaw sweep sector of 20° (+5° / - 15°) having a mean of -5° (as explained above).

[0061] The continuous yawing with the characteristics of the second yaw sweep sector is conducted for another define time period that may be the same or different from the time period of step 110.

[0062] The wait period is then implemented at step 120, which may be the same or different from the wait period of step 111.

[0063] The method then performs the monitoring functions at step 122. If the vibrations have stopped or decreased below the threshold value at step 124, the method reverts to step 104.

[0064] If the blade vibrations have not stopped or decreased below the threshold value at step 126, then the method reverts to step 118 where additional another (nthyaw sweep sector is defined and implemented by the controller. This nthyaw sweep sector has different characteristics than the previous yaw sweep sector.

[0065] The loop between step 126 and 118 may be performed for a predetermined number of attempts before other corrective or preventative actions are taken with the with turbine to prevent damage from the blade vibrations.

[0066] Further aspects of the invention are provided by the subject matter of the following clauses:Clause 1 : A method for reducing vibrations in a blade mounted on a hub of a wind turbine rotor when the rotor is in a stand-still state and a limited yaw capacity state, the method comprising: defining an allowable yaw sweep for the limited yaw capacity state; with a sensor in communication with a controller, monitoring for vibrations in the blade with the rotor at an initial yaw position; upon detection of vibrations in the blade exceeding a threshold level, the controller determining a yaw sweep sector that is within and less than the allowable yaw sweep and issuing a yaw command to a yaw system to yaw the rotor in a continuous back701178-WO-1 / GECW-1281-PCT and forth manner in the yaw sweep sector; continuing to monitor for vibrations in the blade during or after the continuous back and forth yawing of the rotor in the yaw sweep sector; and stopping the continuous back and forth yawing of the rotor when the blade vibrations reduce to below the threshold level.Clause 2: The method of clause 1, wherein a mean position of the yaw sweep sector corresponds to the initial yaw position of the rotor.Clause 3: The method of clause 1 or 2, wherein a mean position of the yaw sweep sector is other than the initial yaw position of the rotor.Clause 4: The method of any preceding clause, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller increasing or decreasing the yaw sweep sector within the allowable yaw sweep.Clause 5: The method of any preceding clause, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller moving a mean position of the yaw sweep sector.Clause 6: The method of any preceding clause, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller changing a characteristic of the continuous yawing of the rotor in the yaw sweep sector.Clause 7: The method of any preceding clause, wherein the characteristic is one or a combination of: a constant rate, a variable rate, or a pulsed rate.Clause 8: The method of any preceding clause, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller performing one or more of the following based on a characteristic of the continued vibrations in the blade: (a) increasing or decreasing the yaw sweep sector within the allowable yaw sweep; (b) moving a mean position of the yaw sweep sector; (c) changing a characteristic of the continuous yawing of the rotor in the yaw sweep sector.701178-WO-1 / GECW-1281-PCTClause 9: The method of any preceding clause, wherein the rotor is yawed to the initial yaw position after the blade vibrations are reduced to below the threshold level.Clause 10: The method of any preceding clause, wherein the rotor is yawed to a position within the allowable yaw sweep other than the initial yaw position after the blade vibrations are reduced to below the threshold level.Clause 11: 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; a plurality of blades mounted on the hub; a yaw system; one or more sensors configured to directly or indirectly detect vibrations in one or more of the blades; a controller in communication with the yaw system and the sensors, the controller configured to perform the following operations: define an allowable yaw sweep for the limited yaw capacity state; monitor for vibrations in the blades with the rotor at an initial yaw position; upon detection of vibrations in the blade exceeding a threshold level, determine a yaw sweep sector that is within and less than the allowable yaw sweep and issue a yaw command to the yaw system to yaw the rotor in a continuous back and forth manner in the yaw sweep sector; continue to monitor for vibrations in the blade during or after the continuous back and forth yawing of the rotor in the yaw sweep sector; and stop the continuous back and forth yawing of the rotor when the blade vibrations reduce to below the threshold level.Clause 12: The wind turbine of clause 11, wherein the controller sets the yaw sweep sector such that a mean position of the yaw sweep sector corresponds to the initial yaw position of the rotor.Clause 13: The wind turbine of clause 11 or 12, wherein the controller sets the yaw sweep sector such that a mean position of the yaw sweep sector is other than the initial yaw position of the rotor.Clause 14: The wind turbine of any preceding clause, wherein the controller is further configured to increase or decrease the yaw sweep sector within the allowable yaw sweep when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector.701178-WO-1 / GECW-1281-PCTClause 15: The wind turbine of any preceding clause, wherein the controller is further configured to move a mean position of the yaw sweep sector when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector.Clause 16: The wind turbine of any preceding clause, wherein the controller is further configured to change a characteristic of the continuous yawing of the rotor in the yaw sweep sector when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector.Clause 17: The wind turbine of any preceding clause, wherein the characteristic is one or a combination of: a constant rate, a variable rate, or a pulsed rate.Clause 18: The wind turbine of any preceding clause, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller is further configured to perform one or more of the following based on a characteristic of the continued vibrations in the blade: (a) increase or decrease the yaw sweep sector within the allowable yaw sweep; (b) move a mean position of the yaw sweep sector; (c) change a characteristic of the continuous yawing of the rotor in the yaw sweep sector.

[0067] 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

701178-WO-1 / GECW-1281-PCTWHAT IS CLAIMED IS:

1. A method for reducing vibrations in a blade mounted on a hub of a wind turbine rotor when the rotor is in a stand-still state and a limited yaw capacity state, the method comprising: defining an allowable yaw sweep for the limited yaw capacity state; with a sensor in communication with a controller, monitoring for vibrations in the blade with the rotor at an initial yaw position; upon detection of vibrations in the blade exceeding a threshold level, the controller determining a yaw sweep sector that is within and less than the allowable yaw sweep and issuing a yaw command to a yaw system to yaw the rotor in a continuous back and forth manner in the yaw sweep sector; continuing to monitor for vibrations in the blade during or after the continuous back and forth yawing of the rotor in the yaw sweep sector; and stopping the continuous back and forth yawing of the rotor when the blade vibrations reduce to below the threshold level.

2. The method of claim 1 , wherein a mean position of the yaw sweep sector corresponds to the initial yaw position of the rotor.

3. The method of claim 1, wherein a mean position of the yaw sweep sector is other than the initial yaw position of the rotor.

4. The method of claim 1, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller increasing or decreasing the yaw sweep sector within the allowable yaw sweep.

5. The method of claim 1, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller moving a mean position of the yaw sweep sector.701178-WO-1 / GECW-1281-PCT6. The method of claim 1 , wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller changing a characteristic of the continuous yawing of the rotor in the yaw sweep sector.

7. The method of claim 6, wherein the characteristic is one or a combination of: a constant rate, a variable rate, or a pulsed rate.

8. The method of claim 1, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller performing one or more of the following based on a characteristic of the continued vibrations in the blade: (a) increasing or decreasing the yaw sweep sector within the allowable yaw sweep; (b) moving a mean position of the yaw sweep sector; (c) changing a characteristic of the continuous yawing of the rotor in the yaw sweep sector.

9. The method of claim 1, wherein the rotor is yawed to the initial yaw position after the blade vibrations are reduced to below the threshold level.

10. The method of claim 1, wherein the rotor is yawed to a position within the allowable yaw sweep other than the initial yaw position after the blade vibrations are reduced to below the threshold level.

11. 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; a pl urali ty of blades mounted on the hub; a yaw system; one or more sensors configured to directly or indirectly detect vibrations in one or more of the blades;701178-WO-1 / GECW-1281-PCT a controller in communication with the yaw system and the sensors, the controller configured to perform the following operations: define an allowable yaw sweep for the limited yaw capacity state; monitor for vibrations in the blades with the rotor at an initial yaw position; upon detection of vibrations in the blade exceeding a threshold level, determine a yaw sweep sector that is within and less than the allowable yaw sweep and issue a yaw command to the yaw system to yaw the rotor in a continuous back and forth manner in the yaw sweep sector; continue to monitor for vibrations in the blade during or after the continuous back and forth yawing of the rotor in the yaw sweep sector; and stop the continuous back and forth yawing of the rotor when the blade vibrations reduce to below the threshold level.

12. The wind turbine of claim 11, wherein the controller sets the yaw sweep sector such that a mean position of the yaw sweep sector corresponds to the initial yaw position of the rotor.

13. The wind turbine of claim 11, wherein the controller sets the yaw sweep sector such that a mean position of the yaw sweep sector is other than the initial yaw position of the rotor.

14. The wind turbine of claim 11, wherein the controller is further configured to increase or decrease the yaw sweep sector within the allowable yaw sweep when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector.

15. The wind turbine of claim 11, wherein the controller is further configured to move a mean position of the yaw sweep sector when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector.701178-WO-1 / GECW-1281-PCT16. The wind turbine of claim 11, wherein the controller is further configured to change a characteristic of the continuous yawing of the rotor in the yaw sweep sector when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector.

17. The wind turbine of claim 16, wherein the characteristic is one or a combination of: a constant rate, a variable rate, or a pulsed rate.

18. The wind turbine of claim 11, wherein when the vibrations in the blade are still above the threshold level after a predetermined time period of the continuous back and forth yawing of the rotor in the yaw sweep sector, the controller is further configured to perform one or more of the following based on a characteristic of the continued vibrations in the blade: (a) increase or decrease the yaw sweep sector within the allowable yaw sweep; (b) move a mean position of the yaw sweep sector; (c) change a characteristic of the continuous yawing of the rotor in the yaw sweep sector.

Images