Investigation of control scheme for PWM VSR under three-phase voltage unbalance conditions

During the design of pulse width modulation voltage source rectifier the power grid is usually supposed in balance. However unbalanced power grid is quite common. Conventional control method, the controller with double current loop (DCL) in positive and negative sequence coordinates, has some disadvantages. This paper proposes a new control strategy which has an optimized design of the controller minimizing negative sequence current (MNSC). The performances between the conventional control scheme of DCL and the control scheme of MNSC are analyzed and compared based on the simulation. The results show that the control scheme of MNSC not only owns similar voltage ripples, but also has little negative sequence current on the condition of the same AC reactance and DC capacitor. Moreover, the control scheme of MNSC is simpler and faster responded than the conventional control scheme.