Direct power control of PWM rectifier with optimal duty ratio under unbalanced network

Direct power control (DPC) attracted wide attention due to its advantages of simple structure, quick response, strong robustness and elimination of current regulation/PWM blocks. However, conventional table-based DPC cannot work well when grid voltage is unbalanced. This paper proposes an improved DPC by using a new definition of instantaneous reactive power. As a result, the distortion in grid current is eliminated and constant active power and new reactive power are obtained. Neither complicated calculation of power compensation nor positive/negative sequence extraction of grid voltage/current is required. The corresponding switching table suitable to regulate both active power and the new reactive power is established. Furthermore, the concept of duty cycle control is introduced to further improve the steady state performance of conventional DPC. Experimental results are presented to confirm the theoretical study and the effectiveness of the proposed method.