Patent ID: 8899920

Claim:
A wind turbine yaw system, comprising: a yaw gear, at least two pinion gears; at least two drive units, wherein each drive unit is associated to one of the at least two pinion gears for driving the respective pinion gear; and a control system, comprising a controller for generating a drive unit control signal for each drive unit for controlling the respective drive unit according to a drive unit reference signal, the drive unit reference signal comprising at least one desired operational parameter value for the respective drive unit so as to realize the at least one desired operational parameter value in the respective drive unit; at least one feedback loop for each drive unit feeding at least one drive unit feedback signal comprising at least an actual value of the at least one desired operational parameter of the respective drive unit back to the controller, each drive unit comprises a frequency converter between the controller and the motor for controlling the speed of the motor, and each feedback signal represents at least an actual value of the at least one desired operational parameter of the respective frequency converter, wherein the controller is adapted to generate the drive unit control signals based on the reference signal and the feedback signals, wherein the drive unit control signals delivered to the frequency converters are chosen such that the difference in the at least an actual value of at least one desired operational parameter values contained in the feedback signals of the two drive units are reduced preferably to zero.