Observer Based Blade-Pitch Control of Wind Turbines operating above rated: a preliminary study

The paper focuses on variable-rotor-speed/variable-blade-pitch wind turbines operating in the region of high wind speeds, where blade pitch and generator torque controllers are aimed at limiting the turbine's energy capture to the rated power value. Preliminary results are presented about a coupled design technique of an observer based blade pitch control input and a generator torque controller, neither of which requiring the availability of wind speed measurements. Closed loop convergence of the overall control system can be proved. Preliminary results about the validation of the control solution using the 5 - MW three-blade wind turbine using the National Renewable Energy Laboratory (NREL) wind turbine simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code