| Doubly-fed induction generator (DFIG) has recently received much attention as one of preferred technology for wind power generation. Compared with conventional generators, the use of DFIG in a wind turbine offers many advantages, such as reduction of inverter cost, the potential to control torque, a slight increase in efficiency of wind energy extraction and the capability of decoupling the control of active and reactive power.This paper concentrates on pitch control and rotor current control of variable speed constant frequency wind turbines with DFIG. The structure of the wind turbines is proposed and the control concept during different wind speeds is described in detail. A simplified model of pitch controlling system is presented. Then a new pitch controller– active-disturbance-rejection controller is proposed to improve the power-output quality of variable speed constant frequency wind turbines. Based on the feedback of rotational speeds, extended-state observers can obtain the disturbances as well as estimated states, which can be precisely cancelled subsequently. Also, this new pitch controller forms nonlinear algorithms to restrain state errors, which leads to the rotational speed ripple reduction. Besides, this paper carries out simulation of the controller under different wind speeds. The result shows that the controller produces good dynamic performance and robustness.Besides, this paper analyses the 5th model of DFIG. A new rotor current controller based on active–disturbance-rejection control theory is proposed to improve the dynamic response of the system under grid voltage disturbances. Simulation results show that the proposed controller can not only tune system power output precisely in normal condition but also ensure prominent reduction of rotor current ripple in order not to be disconnected, which contributes to power system stability. Moreover, the controller takes on good dynamic performances.
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