Emphasis of this article is on the dynamic characteristics analysis of individual pitch control for MW scale directly driven wind turbines with permanent magnet synchronous generator (PMSG). The pitch control objectives were analyzed and the objective expressions were deduced, including power expression, loads expression, and vibration expressions of blade and tower. Then, both the collective pitch control aiming at power control and the individual pitch control strategy aiming at joint power and loads control were analyzed, too. The blade root bending moments and the actual capture power of wind rotor were employed to be the control variables. The power was calculated based on the conventional measured parameters of wind turbines. In order to reflect the difference between the pitch angle command value and the actual value, the pitch actuator dynamic model was used. The research results show that both the collective pitch control strategy and the proposed individual pitch control strategy can effectively control the power injected into grid; moreover, the individual pitch control can reduce fatigue loads; while in the process of individual pitch control, the actual variation of blade pitch angle is closely related to not only the inflow speed but also the blade azimuth angle; individual pitch control strategy can reduce the variation amplitude of flapwise moments, but has little influence on the edgewise moments.
Individual pitch control for mitigation of power fluctuation of variable speed wind turbines
