A wind turbine diagnostic device for diagnosing mechanical damage to generator components of at least one wind turbine, comprising at least one speed sensor for determining a variation over time of the rotational speed of a generator of a wind turbine, the speed sensor having at least one speed signal output for outputting the determined variation over time of the rotational speed, a frequency analysis module and a frequency spectrum signal output for outputting a frequency spectrum, the frequency analysis module determining a frequency spectrum from the determined variation over time of the rotational speed, and a comparator element for comparing a frequency spectrum with a prescribed standard frequency spectrum and for diagnosing mechanical damage to generator components on the basis of the comparison. This increases the possibility of predicting mechanical damage to generator components caused by vibrations.

A wind turbine system comprising a plurality of wind turbines mounted to a support structure including a tower, wherein each of the plurality of wind turbines includes a rotor and a power generation system driven by the rotor, and at least one of a rotor blade pitch adjustment means and a generator power control means. The system further includes control means that receives vibration data associated with the support structure and which is configured to determine a damping control command for a respective one of the plurality of wind turbines, wherein the or each of the wind turbines includes a damping controller that receives a damping control command and which is operable to apply a damping control input to one or both of the blade pitch adjustment means and the generator power control means so as to counteract the measured vibration of the support structure. A benefit of the invention is that the operation of the multiple turbines of the system is used to reduce the effects of structural vibration by damping that vibration in an active manner.

Techniques for controlling the yaw of a wind turbine system by controlling a plurality of yaw drive actuators. Based on a requested motor speed reference as an input signal, and a mean motor speed reference as a feedback signal, the method determines a required motor torque reference as an output signal for the plurality of yaw drive actuators. The plurality of yaw drive actuators rotates a nacelle or a structure comprising a plurality of nacelles such that an even load distribution is provided for the plurality of yaw drive actuators.