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 that can also lead to blade oscillations. Vibrating blades create risk of major potential damages in the entire wind turbine. <CIT> relates to a method for attenuating the oscillation of a rotor blade.

When the wind turbine is in operation, a wind turbine controller may operate directly or indirectly any auxiliary drive system 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 be serious as well in circumstances when the wind turbine is in stand-still conditions, either idling or locked, wherein the blades are susceptible to edgewise oscillations.

At least two types of vibrations may happen during stand-still conditions. The first one is vortex induced vibration (VIV) at certain angles of attack and may or may not include cross flow vortices shed at frequencies close to blade eigen frequencies or system frequencies. The second one is stall induced vibration (SIV) when the angle of attack is close to stall angles 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. There may also be cross flow components to the flow.

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.

When the rotor is locked against rotation, for instance due to installation, commissioning, or maintenance tasks, the blades can experience aero-elastic instabilities, such as the VIV and SIV vibrations. Blades are susceptible to these vibrations when angles of attack are within certain ranges. Because the rotor is locked, rotation of the rotor cannot be used to reduce or damp these vibrations.

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 may increase costs and time for installation and removal of such devices.

Another current practice for wind turbines when not making power includes setting the pitch angle of the rotor blades to substantially <NUM> degrees when the rotor is yawed into the wind and prevented from rotating by means of a locking pin. This particular pitch angle may reduce loads on the blades, at least with some wind conditions. However, the locking pin may suffer from higher loads when the pitch angle is set at the weathervane position and, even in this position, not all vibrations may be avoided, particularly if the wind direction changes over time.

<CIT> proposes a method and system to guard against oscillations of the wind turbine blades when the rotor is locked or idling at low speeds that involves attachment of a releasable cover to the blades that provides a non-aerodynamic surface for a region of the blade. The blade cover is described as a sleeve of a net-like material that can be positioned on the blade either before installation or in the field by service engineers using guidelines.

The present disclosure provides an alternate effective means to reduce or prevent vibrations or oscillations in the wind turbine blades when the wind turbine is in a non-operational mode with the rotor hub unable to yaw and locked or idling via use of unique vibration dampers that will provide benefits in cost, time and ease of installation, and effectiveness.

The present disclosure encompasses a method for preventing or at least reducing vibrations and loads in one or more rotor blades on a rotor hub of a wind turbine when the wind turbine is in a non-operational mode with the rotor hub in a locked or idling condition. This mode of the wind turbine may occur, for example during installation, repair, maintenance, disconnection from a grid, or any other scenario that calls for the rotor hub to be locked against rotation (i.e., at a standstill) or allowed to idle.

The method includes attaching an electronically tunable mass damper at a fixed location on one or more of the rotor blades, the mass damper having a mass component that moves along a stroke path. The mass damper is maintained on the rotor blades during the locked or idling condition of the rotor hub. The method includes sensing movement of the mass component resulting from vibrations or oscillations induced in the rotor blade during the locked or idling condition. The method then automatically tunes the mass damper based on the sensed movement of the mass component by varying an electrical characteristic of the mass damper.

In a particular embodiment, the step of automatically tuning the mass damper is accomplished completely by the mass damper without outside operator or device action. This embodiment may include adjusting operating parameters of the tunable mass damper.

The operating conditions or the vibrations or oscillations may be sensed continuously or periodically with one or more sensors configured in the mass damper.

The method may include tuning the mass damper to an excitation frequency of the rotor blade during the locked or idling conditions, wherein this excitation frequency may change based on a change in the operating conditions experienced by the rotor blade.

A particular benefit of the mass damper is that it is essentially insensitive to changes in environmental or operating temperature. Thus, the mass damper need not be tuned for temperature.

In a particular embodiment, the mass damper is in communication with a remote central controller (e.g., a wind farm controller), wherein operating parameters of the mass damper are remotely adjusted by the remote central controller. In this embodiment, the mass damper may also be in communication with a mobile smart device that is, in turn, in communication with the remote central controller. The operator may adjust the operating parameters of the mass damper via the mobile smart device or via the remote central controller.

In another embodiment, each of the rotor blades is configured with one of the mass dampers, wherein each of the mass dampers is in communication with a wind turbine controller. In turn, the wind turbine controller may be in communication with the remote central controller.

An embodiment of the mass damper includes a flywheel in geared engagement with a rotation damper, wherein the step of remotely tuning the mass damper includes electronically controlling a counter-torque exerted against rotation of the flywheel by the rotation damper.

The flywheel may be in geared engagement with a track gear and rotationally driven as the mass component of the mass damper moves along the stroke path on the rotor blade, wherein the counter-torque exerted by the rotation damper is proportional to a rotational velocity of the flywheel.

In a particular embodiment, the rotation damper includes an electrical generator in geared engagement with and driven by the flywheel, wherein an electrical output of the generator is directly proportional to the rotational velocity of the flywheel and is used to produce the counter-torque. With this embodiment, the tuning process may entail varying an effective electrical load (i.e., a resistive load) placed on the generator to change the counter-torque exerted by the generator at a given rotational speed of the flywheel.

The present invention also encompasses a wind turbine configured for reducing vibrations and loads in rotor blades during a non-operational mode. The wind turbine includes a plurality of rotor blades on a rotor hub, wherein in the non-operational mode of the wind turbine, the rotor hub is in a locked or idling condition. The wind turbine further includes a mass damper attached at a fixed location on one or more of the rotor blades, the mass damper having a mass component that is movable along a stroke path. One or more sensors configured within the mass damper to sense movement of the mass component along the stroke path, wherein the movement is generated by vibrations or oscillations induced in the rotor blades during the locked or idling condition of the rotor hub; and.

wherein the mass damper is automatically tunable by varying an electrical characteristic of the mass damper based on the sensed movement of the mass component.

The mass damper may include a dedicated controller in communication with a remote central controller (directly or via the wind turbine controller) that controls the tuning process automatically or via operator intervention.

The mass damper may also be in communication with a mobile control device (e.g., a smart device) that is in communication with the central controller (or the wind turbine controller) for tuning the mass damper via the mobile control device.

In a particular embodiment, the mass damper includes a flywheel connected to a rotation damper that exerts a counter-torque against rotation of the flywheel, wherein the counter-torque is electronically tunable.

The flywheel may be in geared engagement with a track gear and is rotationally driven as the mass damper moves along a stroke length, wherein the rotation damper comprises an electrical generator in geared engagement with and driven by the flywheel, wherein an electrical output of the generator is directly proportional to the rotational velocity of the flywheel and produces the counter-torque, the generator coupled to a variable effective resistive load (e.g., an effective resistance) for changing the generator output.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> according to the present disclosure. As shown, the wind turbine <NUM> generally 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 embodiment, 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> may be spaced about 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> positioned within the nacelle <NUM> to permit electrical energy to be produced.

The wind turbine <NUM> may also include a wind turbine controller <NUM> centralized within the nacelle <NUM>. However, in other embodiments, the controller <NUM> may be located within any other component of the wind turbine <NUM> or at a location outside the wind turbine <NUM>. Further, the controller <NUM> may be communicatively coupled to any number of the components of the wind turbine <NUM> in order to control the operation of such components and/or implement a corrective or control action. For example, the controller <NUM> may be in communication with individual pitch drive systems associated with each rotor blade <NUM> in order to pitch such blades about a respective pitch axis <NUM>. As such, the controller <NUM> may include a computer or other suitable processing unit. Thus, in several embodiments, the controller <NUM> may include suitable computer-readable instructions that, when implemented, configure the controller <NUM> to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals. Accordingly, the controller <NUM> may generally be configured to control the various operating modes (e.g., start-up or shutdown sequences), de-rating or up-rating the wind turbine, and/or individual components of the wind turbine <NUM>.

The present disclosure relates to situations wherein the wind turbine <NUM> is non-operational (e.g., not producing electrical power) and the rotor <NUM> (and thus the rotor hub <NUM>) is either locked against rotation or is left to idle, for instance due to installation, commissioning, maintenance tasks, or any other reason. The controller <NUM> may remain communicatively coupled to at least the pitch drive system in the locked or idling state of the rotor <NUM>. 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 <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 otherwise unavailable.

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

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) <NUM>, configure the controller to perform the various functions as described herein.

Referring again to <FIG>, each of the rotor blades <NUM> includes a mass damper <NUM> in accordance with aspects of this disclosure mounted thereon, for example at a fixed location that is closer to the blade tip rather than the blade root.

<FIG> is a diagram view of a conventional rotor blade <NUM> that includes an opposite blade root <NUM>, leading edge <NUM>, trailing edge <NUM>, suction side <NUM>, and pressure side <NUM>. The chord-wise dimension <NUM> of the blade <NUM> is also indicated. The mass damper <NUM> is mounted chord-wise onto the suction side <NUM> of the blade <NUM> generally adjacent to the blade tip <NUM>. The mass damper could just as well be mounted onto the suction side <NUM> of the rotor blade <NUM>. The mass damper <NUM> is explained in greater detail below.

<FIG> is a perspective external view of the mass damper <NUM> on the rotor blade <NUM>, and particularly illustrates an embodiment of an attaching system <NUM> for fixing the mass damper on the blade. The attaching system includes opposite clamping shells <NUM> that conform to the blade's outer pressure side surface <NUM> and suction side surface <NUM>. The clamping shells <NUM> extend across the chord-wise width of the rotor blade <NUM> and include a leading-edge flange <NUM> and a trailing edge flange <NUM>. The mass damper <NUM> includes a base <NUM> that extends above one of the clamping shells <NUM> between the flanges <NUM>, <NUM>. The base <NUM> is bolted to the flanges with bolts <NUM>, wherein the bolts <NUM> also serve to bolt the opposite flanges <NUM> together as well as the opposite flanges <NUM>.

It should be appreciated that the mass damper <NUM> may be mounted to the rotor blade using any suitable nonpermanent attaching system, including mechanical fasteners, adhesives, inflatable devices, and so forth.

The mass damper <NUM> includes a housing <NUM> mounted onto the base <NUM>, wherein the working components of the mass damper <NUM> are contained within the housing <NUM>, as described in greater detail below. The housing <NUM> includes side walls <NUM>, end walls <NUM>, and a top <NUM>. It should be appreciated that the housing <NUM> may have any geometric shape.

Referring to the perspective view of <FIG> and the various views of <FIG> and <FIG>, an embodiment of a mass damper <NUM> in accordance with aspects of the invention is provided. The mass damper <NUM> is configured to reduce vibrations and loads in rotor blades during a non-operational mode of the wind turbine wherein the rotor hub in a locked or idling condition. The mass damper <NUM> is mounted to at least one, and preferably all, of the rotor blades (as discussed above) before or shortly after placing the wind turbine in the non-operational mode or during installation of the wind turbine. The mass damper <NUM> is tunable to an excitation frequency of the respective rotor blade or system frequencies as operating conditions experienced by the wind turbine change during the locked or idling condition, as explained in greater detail below.

The mass damper <NUM> includes a mass component <NUM> that moves along a stroke path within the mass damper <NUM>. The term "mass component" is used herein to collectively refer to a mass of the totality of the components on a frame <NUM> (and is inclusive of the frame <NUM>) that move along a track <NUM> within the mass damper <NUM>, as described in more detail below.

The illustrated embodiment of the mass damper <NUM> includes a flywheel <NUM> that is in geared engagement with a rotation damper <NUM>. The mass damper is tuned by controlling and changing a counter-torque exerted against rotation of the flywheel <NUM> by the rotation damper <NUM>. This tuning function is accomplished automatically and wholly by the mass damper <NUM> via an internal electronic controller <NUM> (<FIG>) at any time the mass damper <NUM> is mounted to a rotor blade <NUM>. Thus, as environmental or operating conditions experienced by the wind turbine change during the non-operational mode resulting in a change in vibrations or oscillations induced in the blades, the mass damper <NUM> is effectively and automatically tuned to the change in the vibrations or oscillations.

The flywheel <NUM> is rotationally configured on a frame <NUM> that moves linearly along the chord-wise stroke path within the housing <NUM> relative to the rotor blade <NUM>. The flywheel <NUM> is coupled to a shaft <NUM> that is supported for rotation by bearings <NUM>. The flywheel <NUM> is in geared engagement with the first track gear <NUM> that may be mounted to the base <NUM>, as particularly seen in <FIG>. The track gear <NUM> extends longitudinally along the base <NUM> and effectively defines a length of the stroke path within the mass damper <NUM>. The flywheel <NUM> has a geared outer circumferential surface <NUM> that meshes with the track gear <NUM>. Thus, edge-wise vibrations or oscillations induced in the rotor blade cause the flywheel <NUM> (and mass component <NUM>) to rotate and move linearly back-and-forth along the track gear <NUM>. The mass damper <NUM> is automatically tuned by increasing or decreasing a counter-torque applied to the flywheel <NUM>, as described below.

Although not illustrated in the figures, the flywheel <NUM> may also be in geared engagement with a second track gear mounted to an underside of the top <NUM> of the housing <NUM>.

In the depicted embodiment, the flywheel <NUM> is geared directly to the track gear <NUM> (which may include an additional upper track gear). It should be appreciated that an intermediate gear may be used between the flywheel <NUM> and the track gear <NUM>.

In addition to the weight of the components on (and including) the frame <NUM>, the mass component <NUM> may also include additional ballast weights <NUM> that can be added to or removed from the frame <NUM>, as depicted in the embodiment of <FIG>.

As mentioned, the frame <NUM> (with components fixed thereon) is movable along the track gear <NUM> (which may include an additional upper housing gear) within the housing <NUM>. For this, the frame <NUM> may include a number of rollers <NUM> fixed thereto that ride along bottom runners <NUM> mounted on (or formed integral with) the base <NUM> and top runners <NUM> supported by or formed on the top <NUM> of the housing <NUM>. Side rollers <NUM> may be mounted on the frame <NUM> to roll along the side walls <NUM> of the housing <NUM>. Thus, the frame <NUM> may be supported for direct rolling engagement with the housing <NUM> and base <NUM> via the rollers <NUM>, <NUM>.

Oppositely-acting torsion springs <NUM> are provided to oppose the back-and-forth motion of the frame <NUM> (and attached components) relative to the track gears <NUM>, <NUM>, which also results in dampening of the blade vibrations and oscillations. One end of each spring <NUM> is fixed to the frame <NUM> and the other end of the spring <NUM> is fixed to the shaft <NUM>. Thus, as the shaft <NUM> rotates in either direction, it "tightens" one of the torsion springs <NUM> to generate an opposing force against rotations of the shaft <NUM> (and thus rotation of the flywheel <NUM> fixed to the shaft <NUM>).

The rotation damper <NUM> is mounted on the frame <NUM> and is in geared engagement (direct or indirect) with the flywheel <NUM>. For example, the rotation damper may be in direct geared engagement with the outer circumferential surface <NUM> of the flywheel <NUM>. The rotation damper <NUM> is "rotational" in that it is rotationally driven and produces a counter-torque that opposes rotation of the flywheel <NUM>, this counter-torque being proportional to rotational velocity of the flywheel <NUM>.

In a particular embodiment depicted in the figures, the rotation damper <NUM> includes at least one electrical generator <NUM> in geared engagement with (direct or indirect) and driven by the flywheel <NUM>. In the depicted embodiment, the generator <NUM> is driven by a gear <NUM> that is also in engagement with the outer circumferential surface <NUM> of the flywheel <NUM>. Thus, the generator <NUM> produces an electrical output (i.e., a current) that is directly proportional to the rotational velocity of the flywheel <NUM>. The electrical output produces the counter-torque and, thus, the counter-torque is directly proportional to the rotational velocity of the flywheel <NUM>.

It is a characteristic of electric generators that current from the generator produces a reaction torque (counter-torque) that, at a given load on the generator, is proportional to the magnitude of the current. Torque control of the generator works by changing the effective resistive load placed on the generator. This principle is utilized in the present invention to provide a remote electrical tuning capability to the mass damper <NUM>.

Thus, by changing the effective resistive load on the generator <NUM> felt across the generator terminals, current (and thus counter-torque) produced by the generator <NUM> at a given rotational velocity of the flywheel <NUM> can be varied. A lower effective resistance leads to more current and more counter-torque, thus more damping capability of the mass damper <NUM>. Controlling the effective resistance of the generator load effectively and automatically tunes the damping of the mass damper <NUM>. Embodiments for varying the effective resistive load on the generator are discussed below with reference to <FIG>.

In the embodiment of the mass damper <NUM> depicted in <FIG> and <FIG>, a single generator <NUM> is utilized to provide the tunable damping capability. It should be appreciated that that a plurality of generators <NUM> may be utilized to achieve a desired tuning capability within the constraints of available space on the frame <NUM>. For example, in the embodiment depicted in <FIG>, two generators <NUM> are engaged with the flywheel <NUM>, with both generators <NUM> in communication with a common controller <NUM>.

Referring to <FIG>, the mass damper <NUM> (in particular, the mass component <NUM>) has an effective stroke length in the chord-wise direction across the blade, wherein blade vibrations or oscillations of relatively lower amplitude result in a shorter stroke (shorter path of travel of the frame <NUM> on the track gear <NUM>) and vibrations or oscillations of relatively greater amplitude result in a longer stroke of the mass component <NUM>. Tuning the mass damper <NUM> to the stroke length is accomplished by changing the effective resistive load on the generator, as discussed above. Tuning of the device to limit the travel (i.e., stroke length) at higher vibration/oscillation amplitudes is an important safety feature so that travel of the mass component <NUM> does not exceed the available stroke path/length defined within the mass damper <NUM>. On the other hand, it is desirable to tune the mass damper <NUM> to maximize its performance at lower amplitudes. Thus, the tuning scheme aims to increase stroke at lower amplitudes to maximize performance of the device, while limiting stroke at higher amplitudes to avoid damage to the mass damper <NUM>. Thus, depending on the amplitude of the vibrations/oscillations induced in the rotor blade by the operating conditions experienced by the wind turbine, a desired stroke length is set or defined for the mass damper <NUM> to reduce the amplitude.

The mass damper <NUM> includes a dedicated onboard controller <NUM> to adjust or change the effective resistive load placed on the generator <NUM>, thereby tuning the mass damper. Referring to <FIG>, a sensor array <NUM> is provided on the frame <NUM> and is in communication with the controller <NUM>. This array <NUM> may include one or more sensors. In a particular embodiment, three local sensors are configured in the array <NUM>.

The first local sensor in the array <NUM> may be a position sensor configured to sense the instantaneous position of the mass component <NUM> along the track <NUM> to determine the current operating state of the mass damper <NUM>. This is the main sensor used to provide feedback for the controller <NUM> to adjust the effective resistance on the generator. This first sensor may be, for example an incremental rotary encoder.

The second local sensor in the array <NUM> may be a neutral position sensor configured to provide a pulse (or other indication) at the neutral position of the mass component <NUM> corresponding to the middle of the stroke path. This sensor may be used as a check to ensure that the first sensor (e.g., encoder) is aligned correctly. If the encoder does not agree with the neutral position sensor, the encoder is reset to ensure a correct neutral position. This second sensor may be, for example, an inductive or hall effect sensor on the moving frame <NUM>, and a magnet on the base <NUM>. When the sensor travels over the magnet, a pulse is generated.

The third local sensor in the array <NUM> may be a limit position sensor, such as an inductive/hall effect sensor. This sensor is located on the mass component <NUM> (e.g., on the frame <NUM>) in a way that does not respond to the neutral position sensor. The magnets for this third sensor are placed at the limits of the stroke path/length. If a pulse is detected from this sensor, action is taken to maximize the generator torque to oppose the motion because the moving frame is in danger of exceeding its design stroke.

<FIG> is a simplified circuit diagram that depicts control aspects of the rotation damper <NUM>, particularly the generator <NUM>. The generator <NUM> is engaged with the flywheel <NUM> via the gear <NUM>. An effective resistive load <NUM> is selectively placed across the generator <NUM> and controlled by the controller <NUM> (which may be a conventional PID controller).

In one embodiment, a circuit is established across the generator terminals. The circuit includes a resistive load <NUM> (which may be fixed/non-variable). A relay <NUM> is used to alternately place/remove this resistor <NUM> from the circuit. When the resistor <NUM> is placed across the generator terminals, the generator <NUM> produces an output current, which results in the counter-torque discussed above. This counter-torque is proportional to the generator output (current). A pulse width modulation (PWM) module <NUM> is used to alternately open and close the relay <NUM>. The controller <NUM> adjusts the duty cycle of the PWM module <NUM> to control the amount of time the resistor <NUM> is placed in the circuit. Thus, an increased duty cycle (frequency) of the relay <NUM> results in an increase of the generator output and, thus, an increase in the counter-torque applied to the flywheel. Even though the resistor <NUM> may have a fixed resistance value, the effective resistance seen by the generator is varied by changing the duty cycle of the PWM module <NUM>.

In an alternate embodiment, the resistive load <NUM> may be a variable load, such as a variable resistor indicated by the arrow in <FIG> or a resistor branch circuit wherein multiple resistors are variably combined to change the effective resistive value placed on the generator <NUM>. The PID controller <NUM> may directly control the rheostat or resistor branch circuit to change the effective resistive load <NUM> placed on the generator <NUM> by altering the actual resistive value of the load <NUM>.

The controller <NUM> receives position data via the sensor array <NUM> and controls the effective resistive load <NUM> (by controlling the variable resistor or the duty cycle of the PWM) in an open or closed feedback loop to control the counter-torque produced by the generator <NUM> as a function of stroke length of the mass component <NUM>.

The circuit across the generator <NUM> may include a bypass relay <NUM> controlled by the controller <NUM> for relatively infrequent low voltage operation when maximum counter-torque is required.

Still referring to <FIG>, as mentioned, the controller <NUM> may be an individual dedicated controller configured within the housing <NUM> for each individual mass damper <NUM>. The controller <NUM> may have a dedicated power supply, such as a rechargeable battery <NUM>, or in an alternate embodiment may be supplied with power from a source in the wind turbine.

The controller <NUM> may be in communication with a remotely located central controller <NUM> (directly or via the wind turbine controller <NUM>) for receipt or exchange of control commands or data therewith. For example, the central controller <NUM> may generate control commands to change certain operating parameters of the mass damper <NUM>, such as the stroke length, response characteristics of the mass damper, power modes, duty cycle of the PWM, etc. The controller <NUM> may be in communication with a mobile hand-held controller <NUM> (e.g., a mobile smart device) directly or via an intermediary controller. The mobile controller <NUM> may run an application that allows an operator to monitor operation of the mass damper <NUM> and/or control the operating parameters thereof. In the depicted embodiment, the mobile controller <NUM> and the central controller <NUM> may be in direct communication with the mass damper controller <NUM> via a wireless network <NUM>. The mass damper <NUM> would, in this case, also include wireless transmission and reception capability.

<FIG> depicts a control scheme wherein each rotor blade <NUM> of the wind turbine has one of the mass dampers <NUM> mounted thereon. Each damper <NUM> may have its own dedicated controller <NUM> in communication with the wind turbine controller <NUM> via a wireless network <NUM> or a wired connection. The wind turbine controller <NUM> may, in turn, be in communication with the central controller <NUM> via a wireless network <NUM>. The mobile smart device <NUM> may be in direct communication with the wind turbine controller <NUM> or via the central controller <NUM> (and wireless network <NUM>).

It should be appreciated that various control schemes and architecture may be utilized to provide the automatic tuning capability for the mass dampers <NUM> on the rotor blades <NUM> and remote adjustment or monitoring of the operating state or parameters of the mass dampers <NUM>.

In certain embodiments, one or more sensors <NUM>, <NUM> located on the blades <NUM> or other static locations of the wind turbine may be utilized to provide data indicative of vibrations or oscillations induced in the rotor blades during the locked or idling state of the rotor <NUM>. The oscillations or vibrations may be detected or measured directly by displacement sensors <NUM> (e.g., accelerometers or strain gauges) located directly on the rotor blades. A vibration of a blade may be determined when the strain or deformation parameter satisfies a strain or deformation threshold, which may be determined by the controller <NUM> (or any of the other controllers <NUM>, <NUM>).

The sensors <NUM>, <NUM> may be in communication with the central controller <NUM> directly or via the wind turbine controller <NUM>, as depicted in <FIG>. In order to conserve the internal power supply (e.g., battery <NUM>) in the mass dampers <NUM>, it may be desired that the devices <NUM> are placed in a low-power sleep mode until the vibrations or oscillations induced in the blades reaches a threshold level as determined by the central controller <NUM> based on the data from the sensors <NUM>, <NUM>. Once this threshold is met, the central controller <NUM> may issue a "turn on" command to the mass dampers <NUM> directly or via the wind turbine controller <NUM>.

Claim 1:
A method for reducing vibrations and loads in one or more rotor blades (<NUM>) on a rotor hub (<NUM>) of a wind turbine (<NUM>) when the rotor hub (<NUM>) is in a locked or idling condition, the method comprising:
attaching an electronically tunable mass damper (<NUM>) at a fixed location on one or more of the rotor blades (<NUM>), the tunable mass damper (<NUM>) having a mass component (<NUM>) that moves along a stroke path;
maintaining the mass damper (<NUM>) on the rotor blades (<NUM>) during the locked or idling condition of the rotor hub (<NUM>);
sensing movement of the mass component (<NUM>) resulting from vibrations or oscillations induced in the rotor blade during the locked or idling condition; and
automatically tuning the mass damper (<NUM>) based on the sensed movement of the mass component (<NUM>) by varying an electrical characteristic of the mass damper (<NUM>).