Patent Description:
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises 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 ("directly driven") or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

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. Vibrating blades create risk of major potential damages in the entire wind turbine.

When the wind turbine is in operation, a wind turbine controller may operate directly or indirectly any auxiliary drive systems such as a pitch system or a yaw system to reduce loads on the blades. This way, vibrations of the blades may be counteracted. However, the problem of aero-elastic instabilities can also be serious in circumstances when the wind turbine is in stand-still conditions, either idling or locked. In this condition, edgewise oscillations are a particular concern.

At least two types of vibrations may happen during stand-still conditions. The first one is vortex induced vibration (VIV) when an angle of attack is around <NUM> degrees and vortices shed at frequencies close to blade eigen frequencies. The second one is stall induced vibration (SIV) when the angle of attack is close to stall angles (e.g., <NUM> degrees - <NUM> degrees or other ranges depending on the wind turbine design) and the flow interaction may lead to blade vibrations. The angle of attack may be understood as a geometrical angle between a flow direction of the wind and the chord of a rotor blade.

The vortex and stall induced vibrations are phenomena that, if not adequately designed or compensated for, can lead to blade failure or accelerate blade damage.

A current solution to the cited problems includes the use of aerodynamic devices attached to the blades to reduce vortices and/or increase damping. However, this solution increases costs and time for installation and removal.

The published <CIT> proposes a method for reducing vibrations in the rotor blades of a wind turbine when the wind turbine is in an idling state. Registration means are provided for registering an idling power producing situation of the wind turbine in relation to a utility grid, as well as detection means for detecting edgewise oscillations in one or more of the blades. Control means are used to control the pitch angle of the blades and is adapted for changing the pitch angle when the registration means registers that the wind turbine is operating in an idling power producing situation and the detection means detects edgewise oscillations in one or more of the blades. This solution, however, is reactive in nature in that corrections are not made to the pitch angle until after vibrations are actually detected in blades. These vibrations may potentially cause excessive fatigue and loads on critical components of the wind turbine, such as excessive rotor thrust and torque, individual blade loads, tower loads, and the like.

In addition, the current solutions do not consider the situation wherein grid power is unavailable to the idling wind turbine and only a limited amount (time) of power is available to yaw control system via a backup power supply.

The present disclosure provides examples of operational methods and system for wind turbines that at least partially resolve some of the aforementioned disadvantages.

The present disclosure encompasses a proactive method for preventing or at least reducing vibrations in one or more rotor blades of a wind turbine when the wind turbine is in a standstill idling state with a rotor hub free to rotate. The method is "proactive" in that it does not rely on detection of actual vibrations before taking corrective action but takes action prior to such vibrations being induced in the rotor blades.

The method includes determining a minimum revolution rate of the rotor blades that prevents vibrations of the rotor blades. This rate may be computed in real-time or may be predetermined at stored in an electronic lookup table that is accessed by the wind turbine controller. The method further includes determining that the revolution rate of the rotor blades is below the minimum revolution rate. One or more wind parameters for wind impacting the rotor blades are detected and the controller determines if the wind parameters are above a threshold limit. The method includes determining that grid power is available to the wind turbine and, based on the wind parameters, the controller determines a pitch angle for one or more of the rotor blades to increase rotation of the blades (i.e., the rotor hub) to at least the minimum revolution rate. This pitch angle may be computed in real-time or may be predetermined at stored in an electronic lookup table that is accessed by the wind turbine controller. The controller issues a pitch command to pitch the designated minimum number of rotor blades to the pitch angle. The rotor blades are pitched to increase the revolution rate of the rotor hub prior to vibrations being induced in the rotor blades.

In a particular embodiment, the method includes determining that yaw control is unavailable for the rotor hub prior to pitching the rotor blades. It is presumed that, if yaw control is available, the rotor hub can be yawed to a position relative to the wind to prevent blade vibrations, thereby making pitching of the blades unnecessary.

The wind parameters can vary. For example, the wind parameters, may include wind speed and wind direction, wherein the method determines that the wind speed is above a threshold speed as a prerequisite to pitching the rotor blades. Additional wind parameters, such as wind veer and wind up-flow acting on the rotor blades may also be used to determine the pitch command necessary to achieve a particular orientation of the blades relative to the wind.

Certain embodiments may include determining when grid power is not available to the wind turbine, wherein the rotor blades are pitch using a back-up power supply. In this situation, the method may further include determining (with the controller) a least number of the rotor blades to be pitched to achieve the minimum revolution rate and pitching only the least number of the rotor blades. This embodiment may include monitoring the back-up power supply to each of the rotor blades to ensure that power available to each individual rotor blade does not fall below a minimum power value (which may be the power level needed to feather the rotor blade to a windvane orientation. If a rotor blade designated as one of the minimum number of blades approaches the minimum power level, the controller may isolate the rotor blade from further pitching and designate one or more different rotor blades as the least number of rotor blades to achieve the minimum revolution rate.

The invention also encompasses another embodiment of the proactive method for preventing vibrations in one or more rotor blades when the wind turbine is in a standstill idling state with the rotor hub free to rotate. This embodiment includes determining a minimum revolution rate of the rotor blades that prevents or at least reduces vibrations of the rotor blades and determining that the revolution rate of the rotor blades is below the minimum revolution rate. One or more wind parameters for wind impacting the rotor blades are detected and determined to be above a threshold limit. If it is determined that grid power is not available to the wind turbine for pitching the rotor blades, then the method uses a back-up power supply to pitch the rotor blades. The controller a least number of the rotor blades to be pitched to achieve the minimum revolution rate and pitches only this least number of rotor blades.

The above embodiment may include monitoring the back-up power supply to each of the rotor blades to ensure that available power to each individual rotor blade does not fall below a minimum power value that may be needed to feather the blades. If a rotor blade designated as one of the minimum number of blades approaches the minimum power level, the controller may isolate the rotor blade from further pitching and designate one or more different rotor blades as the least number of rotor blades to achieve the minimum revolution rate.

The present invention also encompasses a wind turbine having a plurality of rotor blades on a rotatable rotor hub, as well as one or more sensors located to detect wind parameters of wind impacting the rotor blades. A pitch system is configured to change a pitch angle of the rotor blades and a controller is in operable communication with the pitch system. When the rotor hub in a standstill idling state and free to rotate, the controller is configured to: determine a minimum revolution rate of the rotor blades that prevents vibrations of the rotor blades; determine that the revolution rate of the rotor blades is below the minimum revolution rate; determine if one or more wind parameters for wind impacting the rotor blades are above a threshold limit; determine that grid power is available to the wind turbine; based on the wind parameters, determine a pitch angle for one or more of the rotor blades to increase rotation of the blades to at least the minimum revolution rate; issue a pitch command to the pitch control system to pitch the rotor blades to the pitch angle; and wherein the rotor blades are pitched to increase the revolution rate of the rotor blades prior to vibrations being induced in the rotor blades.

The wind turbine may include a back-up power supply for the pitch control system, wherein the controller is further configured to: determine when grid power is not available to the wind turbine; determine a least number of the rotor blades to be pitched to achieve the minimum revolution rate; and issue a pitch command to the pitch control system to pitch only the least number of the rotor blades using the back-up power supply. In this embodiment, the controller may also be configured to monitor the back-up power supply to each of the rotor blades to ensure that power available to each individual rotor blade does not fall below a minimum power value and to isolate the rotor blades from being pitched when the power available to the rotor blade reaches the minimum power level. The controller will then redesignate one or more other rotor blades as the least number of rotor blades to achieve the minimum revolution rate.

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) <NUM> may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) <NUM>, configure the controller to perform the various functions as described herein.

<FIG> illustrates a perspective view of one example of a wind turbine <NUM>. As shown, the wind turbine <NUM> includes a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM> mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated example, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. Each rotor blade <NUM> is spaced from the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub <NUM> may be rotatably coupled to an electric generator <NUM> (<FIG>) positioned within the nacelle <NUM> or forming part of the nacelle for producing electrical energy.

The wind turbine <NUM> includes a wind turbine controller <NUM> that may be centrally located within the nacelle <NUM> or external to the nacelle. However, in other examples, the wind turbine controller <NUM> may be located within any other component of the wind turbine <NUM> or at a location outside the wind turbine. Further, the controller <NUM> may be communicatively coupled to any number of components of the wind turbine <NUM> in order to control the operation of such components.

For example, the controller <NUM> may be communicatively coupled to one or more auxiliary drive systems, such as a pitch system <NUM> for adjusting a blade pitch. The auxiliary drive system <NUM> may comprise a yaw system <NUM> for rotating the nacelle <NUM> with the respect to the tower around a rotational axis.

The present disclosure relates to situations wherein the rotor <NUM> is in a standstill state with the rotor hub <NUM> unlocked and free to rotate in an idle mode. The present disclosure contemplates that the controller <NUM> remains communicatively coupled to at least the pitch system <NUM> in the locked state of the rotor <NUM>.

The present disclosure also contemplates that the "controller" function may also be provided by a separate dedicated controller during the locked state of the rotor, as described in the published <CIT>. The dedicated controller may be configured to operate autonomously, i.e., independently from the wind turbine controller <NUM>, 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 <NUM> is a standstill condition with the rotor <NUM> locked.

The wind turbine <NUM> of <FIG> may be placed in an offshore or onshore location.

The wind turbine controller (or "central control system") <NUM> may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like and storing relevant data as disclosed herein). The wind turbine controller may perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals and controlling the overall operation of the wind turbine. The wind turbine controller may be programmed to control the overall operation based on information received from sensors indicating e.g., loads, wind speed, wind direction, turbulence failure of a component, and others.

The wind turbine controller <NUM> may also include a communications module to facilitate communications between the controller <NUM> and the components of the wind turbine and their individual control systems (e.g., a controller for the pitch system <NUM>, a controller for the yaw system <NUM>, a converter control system, and other controls and components.

Further, the communications module may include a sensor interface (e.g., one or more analog-to-digital converters) to permit signals transmitted from one or more wind parameter sensors or load sensors to be converted into signals that can be understood and processed by the controller <NUM>. It should be appreciated that the sensors may be communicatively coupled to the communications module using any suitable means as, for example, a wired connection or a wireless connection.

<FIG> illustrates a simplified, internal view of one example of the nacelle <NUM> of the wind turbine <NUM> of the <FIG>. As shown, the generator <NUM> may be disposed within the nacelle <NUM> and coupled to the rotor <NUM> for generating electrical power from the rotational energy generated by the rotor <NUM>. For example, the rotor <NUM> may include a main rotor shaft <NUM> coupled to the hub <NUM> for rotation therewith. The generator <NUM> may then be coupled to the rotor shaft <NUM> such that rotation of the rotor shaft <NUM> drives the generator <NUM>. For instance, in the illustrated embodiment, the generator <NUM> includes a generator shaft <NUM> rotatably coupled to the rotor shaft <NUM> through a gearbox <NUM>.

It should be appreciated that the rotor shaft <NUM>, gearbox <NUM>, and generator <NUM> may generally be supported within the nacelle <NUM> by a support frame or bedplate <NUM> positioned atop the wind turbine tower <NUM>.

The nacelle <NUM> is rotatably coupled to the tower <NUM> through the yaw system <NUM> in such a way that the nacelle <NUM> is able to rotate about a rotating axis or "yaw axis" RA as depicted in <FIG>. The yaw system <NUM> comprises a yaw bearing having two bearing components configured to rotate with respect to the other. The tower <NUM> is coupled to one of the bearing components and the bedplate or support frame <NUM> of the nacelle <NUM> is coupled to the other bearing component. The yaw system <NUM> comprises an annular gear <NUM> and a plurality of yaw drives <NUM> with a motor <NUM>, a gearbox <NUM> and a pinion <NUM> for meshing with the annular gear <NUM> for rotating one of the bearing components with respect to the other.

The blades <NUM> are coupled to the hub <NUM> with a pitch control system <NUM> that includes a pitch bearing <NUM> between the blade <NUM> and the hub <NUM>. The pitch bearing <NUM> comprises an inner ring and an outer ring (shown in <FIG>). The wind turbine blade <NUM> may be attached either at the inner bearing ring or at the outer bearing ring, whereas the hub <NUM> is connected at the other bearing ring. A blade <NUM> may perform a relative rotational movement with respect to the hub <NUM> when the pitch control system <NUM> is actuated. The rotational movement is performed around a pitch axis PA and thus can be measured in degrees. The inner bearing ring may therefore perform a rotational movement with respect to the outer bearing ring. The pitch control system <NUM> of <FIG> comprises a drivable pinion <NUM> that meshes with an annular gear <NUM> provided on the inner bearing ring to set the wind turbine blade <NUM> into rotation. Individual motors are provided for rotationally driving the pinions <NUM>. In an operating state of the wind turbine <NUM> wherein the wind turbine is producing power and connected to a grid, power to drive the pitch motors is supplied from the grid or generator output.

Even though the pitch axis is shown for only a single blade <NUM>, it should be clear that each of the blades120 has such a pitch axis. A single pitch system or a plurality of individual pitch systems may be used to rotate the respective blades <NUM> around their longitudinal axes.

In the standstill idling state of the wind turbine <NUM> with the rotor <NUM> free to rotate, the wind turbine is not generating electrical power and is likely not receiving electrical power from a grid. In such instances, the wind turbine <NUM> further includes a dedicated power source <NUM> (<FIG>), which may comprise a battery or a super-capacitor (not illustrated) that stores a predefined amount of energy to supply the controller <NUM> (or a dedicated controller) and the auxiliary drive system <NUM>, <NUM> for a predefined period of time. In alternative examples, the dedicated power source <NUM> may comprise a fuel generator, such as a diesel generator. As discussed in greater detail below with respect to <FIG>, the dedicated power source <NUM> may include individual power sources for each of the pitch motors.

As discussed in greater detail below, aspects of the present disclosure rely on detection of wind parameters acting on the blades <NUM>, such as wind direction and speed. Referring to <FIG> and <FIG>, the wind turbine <NUM> may include one or more wind parameter sensors <NUM> for measuring various wind parameters upwind of the wind turbine <NUM>. For example, as shown in <FIG>, one sensor <NUM> may be located on the hub <NUM> so as to measure an actual wind parameter(s) upwind from the wind turbine <NUM>. The actual wind parameter(s) may be any one or combination of the following: wind gust, wind speed, wind direction, wind acceleration, wind turbulence, wind shear, wind veer, wake, and wind up-flow. Further, the one or more sensors <NUM> may include at least one LIDAR sensor for measuring upwind parameters. For example, the sensor <NUM> in the hub <NUM> may be a LIDAR sensor, which is a measurement radar configured to scan an annular region around the wind turbine <NUM> and measure wind speed based upon reflection and/or scattering of light transmitted by the LIDAR sensor from aerosol. The cone angle (θ) 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.

In further embodiments as depicted in <FIG>, the one or more LIDAR sensors may also be located on the wind turbine tower <NUM>, on one or more of the wind turbine blades <NUM>, on the nacelle <NUM>, on a meteorological mast of the wind turbine, or at any other suitable location. In still further embodiments, one or more wind parameter sensors <NUM> may be located in any suitable location in proximity to the wind turbine <NUM>. The sensors <NUM> may be configured to measure a wind parameter ahead of at least one specific portion, typically the most significant sections of the blades <NUM> in terms of contributions of those sections to aerodynamic torque on the blades <NUM>. These sections may include, for example, sections close to the tip of the blade.

In alternative embodiments, the sensors <NUM> need not be LIDAR sensors and may be any other suitable sensors capable of measuring wind parameters upwind of the wind turbine <NUM>. 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 (SODAR) sensors, infra lasers, radiometers, pitot tubes, rawinsondes, other optical sensors, and/or any other suitable sensors. It should be appreciated that, as used herein, 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 <NUM> may, for example, be used to generate signals relating to the parameter being monitored, which can then be utilized by the controller <NUM> to determine the actual wind condition.

Other aspects of the present disclosure may rely on the determination of loads acting on certain components of the wind turbine <NUM>. Referring to <FIG> and <FIG>, load sensors <NUM> may be utilized for measuring a deformation of one or more of the relevant components, such as the blades <NUM>, tower <NUM>, bed plate, as so forth. Such sensors may be strain sensors that detect a deformation/strain parameter of the component.

In other embodiments, the loading conditions on various components of the wind turbine <NUM> may be indirectly determined. For example, the controller <NUM> (or other controller in communication with the controller <NUM>) may receive operating data may consist of any or combination of the following: a pitch angle, a generator speed, a power output, a torque output, a temperature, a pressure, a tip speed ratio, an air density, or other similar operation condition. The controller then calculates an estimated load condition as a function of various combinations of the operating data. In one embodiment, for example, the controller may implement an estimator functionality with a control algorithm having a series of equations to determine the estimated load condition as a function of the pitch angle, the generator speed, the power output, and the air density. Further, the equations may be solved using the operating data and one or more aerodynamic performance maps. In one embodiment, the aerodynamic performance maps are dimensional or non-dimensional tables that describe rotor loading and performance (e.g., power, thrust, torque, or bending moment, or similar) under given conditions (e.g., density, wind speed, rotor speed, pitch angles, or similar). As such, the aerodynamic performance maps may include power coefficient, thrust coefficient, torque coefficient, and/or partial derivatives with respect to pitch angle, rotor speed, or tip speed ratio. Alternatively, the aerodynamic performance maps can be dimensional power, thrust, and/or torque values instead of coefficients.

<FIG> depicts a configuration of the pitch control system wherein an individual pitch motor <NUM> is assigned to drive the pinion <NUM> (<FIG>) at each rotor blade <NUM>. The controller <NUM> is in operable communication with a controller associated with each pitch motor <NUM>. As mentioned, in an operating state of the wind turbine, power is supplied to the pitch motors <NUM> from grid power <NUM>. For situations wherein grid power is not available, the backup power supply <NUM> (<FIG>) is provided by an individual backup power supply <NUM> (such as a battery, super capacitor, diesel or gas generator, or the like) associated with each pitch motor <NUM>. The individual backup power supplies <NUM> are in communication with the controller <NUM>. A backup power supply <NUM> may also be provided for the controller <NUM>.

Referring to <FIG>, an embodiment of a method <NUM> in accordance with aspects of the present invention is depicted in flowchart form. At step <NUM>, the idling state of the rotor hub is detected by the controller. Specially, it is determined that the rotor hub is not locked and is free to rotate. The dashed lines in <FIG> are meant to convey that this step <NUM> may be performed in conjunction with any number of other steps in the process.

At step <NUM>, a minimum revolution rate of the rotor hub (and blades) that will prevent or substantially reduce vibrations being induced in the rotor blades. This revolution rate may be predetermined (e.g., empirically or via modeling) and stored in an electronic lookup table that is accessible by the controller. Alternatively, this value may be computed in real-time by the controller.

At step <NUM>, the determination is made that the rotor hub is rotating at a rate less than the minimum revolution rate from step <NUM>. The rotational rate of the rotor hub may be measured directly or derived from other parameters. If the revolution rate of the rotor hub is above the minimum revolution rate of step <NUM>, then the method does not proceed further.

At step <NUM>, one or more wind parameters of interest (e.g., wind speed) are determined via the sensors discussed above. These parameters may include, for example, any one or combination of wind direction, wind speed, wind veer, and wind up-flow. Wind veer is understood to mean wind direction variations with respect to vertical height. Wind up-flow is understood to mean an angle of the wind with respect to horizontal. Step <NUM> also includes a determination of whether the wind parameter(s) of interest are above a threshold value. For example, if wind speed is detected, the determination is made that the wind speed is at a value known to induce vibrations in the blades. If the wind speed is below the threshold value, then the method does not proceed further.

The dashed lines in <FIG> indicate that steps <NUM> through <NUM> may be carried out essentially in parallel.

At step <NUM>, the determination is made that grid power is available for the pitch control system. If grid power is not available, then the method relies on backup power supplies, as discussed in greater detail below.

At step <NUM>, a pitch angle is determined for the rotor blades that will generate rotations of the rotor hub above the minimum rotational rate of step <NUM>. Since grid power is available, it may be preferable to pitch all of the blades so that each blade contributes to increased rotation of the rotor hub. Pitching less than all blades is also an option. The pitch angles for various wind parameters may be computed in real-time by the controller or may be predetermined (e.g., based on modeling or empirically determined) and stored in an electronic database (i.e., a lookup table) that is accessible by the controller. Thus, the step of determining the pitch angles includes accessing and retrieving a stored value of the pitch angle of attack for the detected wind parameters.

At step <NUM>, the controller issues a pitch command to the rotor blades to achieve the pitch angle determined in step <NUM>.

<FIG> depicts an alternate method embodiment <NUM> in flowchart form. At step <NUM>, the idling state of the rotor hub is detected by the controller. Specially, it is determined that the rotor hub is not locked and is free to rotate. The dashed lines in <FIG> are meant to convey that this step <NUM> may be performed in conjunction with any number of other steps in the process.

At step <NUM>, one or more wind parameters of interest (e.g., wind speed) are determined via the sensors <NUM> discussed above. These parameters may include, for example, any one or combination of wind direction, wind speed, wind veer, and wind up-flow. Wind veer is understood to mean wind direction variations with respect to vertical height. Wind up-flow is understood to mean an angle of the wind with respect to horizontal. Step <NUM> also includes a determination of whether the wind parameter(s) of interest are above a threshold value. For example, if wind speed is detected, the determination is made that the wind speed is at a value known to induce vibrations in the blades. If the wind speed is below the threshold value, then the method does not proceed further.

At step <NUM>, the determination is made that grid power is unavailable for the pitch control system. If grid power is not available, then the method relies on backup power supplies at step <NUM>.

At step <NUM>, the determination is made as to the minimum number of blades (and pitch angle) that need to be pitched to generate the minimum revolution rate of step <NUM>. Because the backup power supplies are limited by capacity (and thus operational time), the goal is to preserve as much capacity from the backup power supplies as possible. For example, if only one blade can be pitched to achieve the minimum revolution rate, then the power supplies associated with the other blades can be preserved. The backup power supplies can be monitored to ensure that enough reserve remains in each supply to ensure that the respective blade can be feathered to an orientation in order to stop rotation of the rotor hub.

At step <NUM>, only the minimum number of blades determined in step <NUM> are pitched to increase rotation of the rotor hub (and blades).

<FIG> and <FIG> are a block diagram representing various other method embodiments. It should be appreciated that not all of the steps depicted in <FIG> and <FIG> are necessary for any one embodiment. Various combinations of the steps depicted in <FIG> and <FIG> are within the scope of the present disclosure.

Referring to <FIG>, the method <NUM> includes step <NUM> wherein an initial state of the rotor hub is detected by the controller to determine if the rotor hub is idling and free to rotate (i.e., is not locked against rotation).

At step <NUM>, if the rotor hub is not idling, then the process proceeds directly to step <NUM> wherein the pitch control process is off (not activated). This condition may be present, for example, in a standstill state of the wind turbine wherein the rotor is locked.

At step <NUM>, if it is determined by the controller that the rotor hub is idling, then the process proceeds to step <NUM> wherein the controller determines the yaw state of the rotor. If the rotor is able to yaw, then at step <NUM> the process diverts to step <NUM> and the pitch control process is not activated. This step may be desired when it is determined that the ability to yaw to the rotor hub provides sufficient capability to place the blades in a relative position with respect to the wind that prevents the blades from vibrating.

At step <NUM>, if it is determined by the controller that the yaw system is non-operable, then the process proceeds to step <NUM> wherein the one or more wind parameters are determined, which may include one or both of wind direction and wind speed.

At step <NUM>, the determination is made as to whether the wind parameter (e.g., wind speed) exceeds a threshold value that requires further action by the pitch control system to prevent blade vibrations. If the wind parameter does not exceed the threshold value, then corrective action is not needed and the pitch control process reverts to step <NUM> and is not activated.

If the wind parameter exceeds the threshold value at step <NUM>, then the process proceeds to step <NUM> wherein the revolution rate of the rotor is determined by the controller.

At step <NUM>, the determination is made as to whether the revolution rate of the rotor exceeds a defined threshold value. If it does, then the assumption is that the rotor is rotating at a sufficient rate to prevent vibrations from being induced in the blades and the process reverts to step <NUM> and the pitch control process ceases. If the rate does not exceed the threshold value, then the process proceeds to multiple steps <NUM>-<NUM>, which may be performed concurrently or sequentially.

At steps <NUM> and <NUM>, if not done at step <NUM>, wind direction and wind speed are measured. Additional wind parameters may also be measured, such as wind up-flow at step <NUM> and wind veer at step <NUM>.

At step <NUM>, the orientation of the blades may be determined based on a number of factors, such as the rotor position (e.g., determined by rotor position sensors), yaw position relative to wind direction, turbine geometry (e.g., shaft tilt, cone shape, blade pre-bend, blade twist, etc.) and pitch angle. The blade orientation may be used as a consideration for determining the pitch command for an individual blade.

Referring to <FIG>, the process continues to step <NUM> wherein the controller determines a pitch command for all of the blades that is sufficient to increase the revolution rate of the rotor above the threshold value.

At step <NUM>, the state of grid power available to the wind turbine is detected. If grid power is available at step <NUM> to drive the pitch motors, then the process proceeds to step <NUM> wherein the controller issues the pitch command to all of the blades. The blades are then pitched to increase the revolution rate of the rotor.

If grid power is not available at step <NUM>, the process proceeds to step <NUM> wherein it is determined if backup power is available to pitch the blades. If backup power is not available (as well as grid power being unavailable), the process reverts to step <NUM> and ceases.

If backup power is available at step <NUM>, then the process proceeds to step <NUM> wherein the controller determines the minimum number of blades (and pitch angle) that are need to increase revolutions of the rotor to at least the threshold value. For example, if grid power is available at step <NUM>, then all of the rotor blades can be used. However, if grid power is not available, then it is desirable to use a minimum number (e.g., one) of the blades to preserve backup power to the other blades.

At step <NUM>, the controller issues the pitch angle command to the minimum number of blades, which are then pitched.

At step <NUM>, the process continues to monitor the backup power supplies for the blades, particularly for the blade that is being pitched. The intent is to ensure that sufficient power exists for a final pitch wherein the blade is feathered to a position to prevent lift. When the power supply for the blade being pitched reaches a defined minimal level, the controller will isolate this blade and redesignate one or more of the other blades for pitching.

Claim 1:
A proactive method for preventing vibrations in one or more rotor blades of a wind turbine when the wind turbine is in a standstill idling state with a rotor hub free to rotate, the method comprising:
determining a minimum revolution rate (<NUM>) of the rotor blades that prevents vibrations of the rotor blades;
determining that the revolution rate of the rotor blades is below the minimum revolution rate (<NUM>);
detecting one or more wind parameters for wind impacting the rotor blades and determining if the wind parameters are above a threshold limit (<NUM>);
determining that grid power is available to the wind turbine (<NUM>);
based on the wind parameters, with a controller, determining a pitch angle (<NUM>) for one or more of the rotor blades to increase rotation of the blades to at least the minimum revolution rate;
with the controller, pitching the rotor blades to the pitch angle (<NUM>); and characterized in that the rotor blades are pitched to increase the revolution rate of the rotor blades prior to vibrations being induced in the rotor blades.