Coordinated control strategy of doubly fed wind power generation system under unbalanced grid voltage

A coordinated control method for doubly fed wind power generation system under unbalanced grid voltage is presented in this paper, which can remove the negative effects of unbalanced voltage on the doubly fed induction generator (DFIG) such as the unbalance of stator and rotor current. And the method can suppress the double frequency oscillations of the output active and reactive power. To improve the operating performance, the operation mechanism of DFIG system with a series grid side converter (SGSC) under unbalanced grid voltage is described firstly, and the strategy for series grid side converter aiming at maintaining the stator three phase voltage balance is proposed, and then the stator and rotor currents will keep balanced. Meanwhile, the mathematical model of the parallel grid side converter (PGSC) is analysed under unbalanced grid voltage and the double frequency power control equation is established. According to the control equation, a control strategy based on a proportional resonance (PR) power compensator for the parallel grid side converter is put forward, then the control goal of suppressing the double frequency oscillations of the output active and reactive power of the whole system simultaneously is accomplished, which improves the output quality of the system and ensures the safe operation of the connected grid. The proposed coordinated control strategy in this paper verified by the simulations of a doubly fed wind power generation system model built in PSCAD/EMTDC.