ABSTRACT
The main objective of wind turbine control is to make wind power production economically more efficient. This objective is often achieved in two distinct regions, i.e., the below rated wind speed and the above rated wind speed regions. In the below rated wind speed region, generator torque control is used primarily to control rotor speed to track the maximum power coefficient in order to maximize energy capture. In the above rated wind speed region, the blade pitch control is used primarily to regulate the rotor speed in order to regulate the aerodynamic power within its design limit [1]. As the wind turbine sizes are increasing and their mechanical components are built lighter, the reduction of the structural loads becomes a very important task of wind turbine control because structural loads can reduce turbine reliability and lifespan and also may cause power fluctuations. In particular, the reduction of blade loads has received special interest. Wind speed variations across the turbine rotor during rotor rotation, which is caused by the large rotor blade size, the wind shear, turbulence and tower shadow effects, cause periodic oscillations in blade structural loads, and
this structural load is especially important in the above rated wind speed region because high structural loads arise from strong winds. Therefore the individual pitch control is sometimes considered since common collective pitch control cannot compensate for the periodic loads on the blades.
