The circulating current in paralleled three-phase boost PFC rectifiers

This paper presents modeling, simulation, and experimental results of paralleled three-phase boost PFC rectifiers. The first part of the paper describes the overall system set-up and control schemes of the PFCs. Although individual modules work as expected, a low frequency oscillation between the paralleled units was observed. Because the conventional model of the three-phase rectifier cannot predict this kind of interaction, an average model is developed for system simulation. From this model, it is shown that the interleaved discontinuous space vector modulation produces a periodic disturbance on the zero axis. Because the conventional control in a balanced three-phase system with only dq channels cannot reject this disturbance, a circulating current will flow between the paralleled modules. Based on this observation, a space vector modulation with control in the third axis is proposed for the parallel operation of the rectifiers. Simulations are done to show the feasibility of this scheme