Pitch control system is the most important part of wind turbine to keep the rotor speed within its design limit. Large scale wind turbines usually adopt PI controller to adjust rotor speed above the rated wind speed. Since wind turbine system is a high-order nonlinear system, one set of PI parameters can't achieve excellent control performance, especially when wind turbulence is very strong. In view of the shortcoming of conventional PI controller and nonlinear characteristics of wind turbines, an expert PID controller based on a trackingdifferentiator is researched in this paper. The trackingdifferentiator is used to arrange transitions of the control variables, such as the speed, and extract the one-order differential signal reasonably, which has the potential to cope with the nonlinear characteristics of wind turbines. The simulation results show that proposed controller can effectively restrain the overshoot of machine's rotor speed and has better control performances than conventional PI controller.

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