A method for operating a wind turbine is provided. The wind turbine includes a rotor with at least one rotor blade. The method includes determining an actual value of at least one of a first variable indicative of a failure state of the wind turbine and a second variable of the wind turbine correlated to a status of the wind turbine or an ambient status. The method further includes estimating an occurrence of a detrimental overspeed state of the wind turbine from at least one of the determined actual values, wherein a variable speed limit is adjusted based on the result of the estimation. The method further includes operating the wind turbine having regard to the variable speed limit. A control system for performing this method and a wind turbine including the control system is provided.

A method of determining a blade clearance during operation of a wind turbine is provided, the blade clearance corresponding to a distance between a rotor blade and a tower of the wind turbine. The method includes (a) detecting a rotor blade velocity, (b) emitting a first signal from an observer location, the first signal having a first frequency, (c) receiving a second signal at the observer location, the second signal being reflected from the rotor blade when the first signal impinges on the rotor blade, (d) determining a Doppler shift of the second signal relative to the first signal, and (e) determining the blade clearance based on the first frequency, the Doppler shift, the observer location, and the rotor blade velocity, wherein the step of determining the blade clearance utilizes a mathematical model. A corre-sponding system and a wind turbine comprising such a system are also provided.

A system and method for monitoring and controlling the deflection of rotor blades of a wind turbine so as to prevent tower strikes is disclosed. The method includes operating the wind turbine at standard pitch angle settings. Another step includes monitoring a loading condition of the wind turbine over a predetermined time period. A further step includes tracking a number of wind condition deviations of a certain magnitude occurring during a predetermined time period. The method also include altering one or more of the standard pitch settings of the rotor blades in response to the number of wind condition deviations exceeding a wind deviation threshold and/or the loading condition exceeding a loading threshold as an exceedance indicates an increased probability of rotor blade deflection. The method further includes performing one or more additional corrective actions so as to reduce the probability of a rotor blade tower strike.

Method of operating a wind turbine having a tower, a rotor with a plurality of blades arranged on the tower, one or more pitch systems for pitching the blades, a system for determining an instantaneous representative wind speed, and a system for determining a distance between a blade and the tower. The method comprises determining the instantaneous representative wind speed, and determining the distance between the tower and one of the blades when said blade is in the shadow of the tower. The method further comprises determining a tower distance pitch adjustment depending on the determined distance between the tower and the blade in the shadow of the tower and on the determined instantaneous representative wind speed. The method still further comprises the one or more pitch systems applying the determined tower distance pitch adjustment to at least the next blade to be in the shadow of the tower.

The present subject matter is directed to a method for operating a wind turbine. The method includes calculating one or more blade root loads, e.g. a blade root resultant moment, of at least one rotor blade of the wind turbine. Another step includes estimating a span-wise loading of the rotor blade based at least partially on the one or more blade root loads. The method also includes determining a deformation margin of the rotor blade based at least partially on the span-wise loading and one or more estimated deformations occurring on the rotor blade. Another step includes controlling the wind turbine based on the deformation margin.

A method for controlling a wind turbine to decrease blade deflection during tower passage is disclosed. A blade flap moment of the wind turbine blades is measured. A blade flap moment of the wind turbine blades and a rotor tilt moment in a situation where the pitch offset has not been added are estimated, based on the measured blade flap moment. In the case that the estimated blade flap moment exceeds a first activation threshold value and the estimated rotor tilt moment exceeds a second activation threshold value, individual pitch angle adjustment of the wind turbine blades is initiated by adding a pitch offset, at azimuth angles within an azimuth adjustment region corresponding to tower passage of the wind turbine blades.

Systems and methods for controlling operation of one or more auxiliary circuits in a wind turbine system are provided. For instance, a grid event associated with the wind turbine system can be detected. In response to the grid event, a control signal can be provided to an auxiliary circuit breaker of the wind turbine system. The auxiliary circuit breaker can be associated with one or more auxiliary circuits that are not directly in a power production path of the wind turbine system. The auxiliary circuit breaker can disconnect the one or more auxiliary circuits from the grid based at least in part on the control signal.

Systems and methods for preventing excessive loading on a wind turbine are disclosed. The method includes: measuring an actual wind parameter upwind from the wind turbine using one or more sensors; providing the measured wind parameter to a processor; providing a plurality of wind turbine operating data to the processor; utilizing the plurality of operating data to determine an estimated wind turbine condition at the wind turbine; generating a control wind profile based on the actual wind parameter and the estimated wind turbine condition; and, implementing a control action based on the control wind profile to prevent excessive loading from acting on the wind turbine.

A double fed induction generator (DFIG) converter, methods and computer readable mediums are presented in which rotor side current spikes are attenuated by selectively activating at least one series damping circuit to conduct current through a series damping circuit resistance coupled in series between one or more DFIG rotor leads and a grid side converter in response to a grid fault occurrence or a grid fault clearance, and selectively bypassing the series damping circuit resistance after activating the series damping circuit.

A method and controller for controlling the torque in a wind turbine is described wherein the wind turbine is configured to deliver power via a converter to a public grid. The method comprises the steps of: receiving a fault signal; and, in response to said fault signal, a converter controller controllably ramping down the torque of said turbine from a nominal torque value to a predetermined low torque value within a predetermined time window selected from 0.2-2 seconds, preferably 0.5-1.5 seconds.