Nonlinear pitch control design for load reduction on wind turbines

As the modern wind turbines (WTs) become larger and larger in size, the structural loads experienced by WTs increase dramatically. Such loads will shorten the working life of WTs and increase the maintenance cost. To mitigate such loads, this paper proposes a nonlinear pitch control strategy for WTs operating in the above-rated wind speed region. With the proposed strategy, nonlinear dynamic inversion method is employed to transform the non-affine nonlinear WT model into a pseudo linear one. Then the linear control theory can be applied for control design. The simulation results based on the aero-elastic model of Fatigue, Aerodynamics, Structures, and Turbulence (FAST) verify the superiority of the proposed nonlinear controller over the tranditional gain-scheduled proportional-integral (GSPI) controller. The proposed nonlinear controller can work well in the whole above-rated wind speed region, and easy to implement in the real application.