Abstract: In order to solve the zero-sequence circulating current problem existing in two parallel three-phase PWM rectifiers,by analyzing their equivalent average models,a mathematical model of the zero-sequence circulating current of the parallel system is constructed in a two-phase synchronous rotating coordinate system.Then,the control principle of the circulating current is discussed,and the symmetrical SVPWM ( Space Vector Pulse Width Modulation) control strategy with a variable zero vector duty cycle is explored.On this basis,a control strategy of the circulating current,which combines the repetitive control with the PI control,is designed,and a novel deadbeat control strategy is then proposed to suppress the circulating current by adjusting the voltage zero vector of SVPWM.The proposed strategy can effectively suppress the circulating current without additional hardware,and it has a fast dynamic response.Experimental results demonstrate that the model analysis is correct,and the proposed strategy can solve such problems as waveform distortion,current discrepancy and inductors unbalance.Thus,the system reliability is greatly improved.

Key words: parallel, zero-sequence circulating current, PWM rectifier, space vector pulse width modulation, deadbeat control