In this paper, the power quality in a wind power generation system is studied. It is shown that adding a Series Grid-Side Converter (SGSC) to the Doubly Fed Induction Generator (DFIG) structure and applying a suitable control algorithm will make the system be able to compensate the adverse effects of the voltage unbalance and consequently can improve the power quality. In order to decrease design complexity and implement the control algorithms in the stationary reference frame, a Sliding-Mode Control (SMC) method for controlling of the DFIG system with SGSC is proposed. One of the advantages of the proposed method in this paper is its robustness to parameter variations both in the DFIG and the connected network. Moreover, the designed controller leads to a fast dynamic response. It should be mentioned that, a coordinated control carries out between SGSC with the other DFIG converters. The simulation results approve the validity of the mentioned advantages and the effectiveness of the proposed method.