Modeling of active yaw systems for small and medium wind turbines

This paper proposes the use of an active yaw system to protect small and medium wind turbines in the high wind zone from overloading. The active yaw system turns the rotor partially out of the wind to decrease the turbine power. The dependency of the power on the yaw angle is modeled by the third power of the cosine of the yaw angle. A proper controller is configured based on on-off control of the yaw mechanism. A supplementary rotor speed control is required to avoid static instability. The proposed power limitation strategy is simulated in dynamic situations. The step response simulations show that a yaw rate of the order of 3°/s is required to properly limit the power. Simulations using a realistic wind profile demonstrate that the system can cope with the fluctuating nature of the wind.