A novel control system for offshore wind turbines under the effects of ice and tide

This paper summarizes (1) the dynamic model of a general purpose offshore wind turbine (WT) operating under the effects of ice and tide, and (2) the design of a novel torque control system able to reduce the mechanical fatigue of the turbine in these extreme weather conditions. By examining the frequency response and model uncertainty of the WT, this work shows the challenging effects of ice and tide, which increase the amplitude of tower vibrations at some particular frequencies, creating greater mechanical fatigue. To counteract these effects, the paper also develops a novel torque control system, varying the generator torque in the above rated wind speed region, while (a) meeting the thermal specifications of the power converters and generator and (b) maintaining an average torque over time that continues to produce the rated power of the WT. The control strategy is validated with a realistic nonlinear simulator.