Analysis and Control of Switching Circulating Currents in Multi-Module Parallel SPWM Converters

High-frequency switching circulating currents are inevitable in multi-module parallel connected converters, which will result in increased power losses and declined system stability, reliability and control precision. In view of this, the formation mechanism of the switching circulating currents is first researched at both power switch level and circuit level in this paper. Next, the switching circulating currents in an N-module converter based on the sinusoidal pulse width modulation (SPWM) technique are mathematically modeled. On this basis, their distribution characteristics in terms of carrier phase deviation are analyzed in detail. In particular, a typical case considering the carrier phase shifting SPWM technique is utilized to further explore the circulating current distribution features. Then, three typical voltage and current closed-loop control approaches considering LCand LCL-type filters are studied, for the purpose of developing an optimum solution for the circulating current inhibition. The theoretical analysis and experimental results validate the effectiveness of the proposed analysis means and the restraining strategy of the high-frequency switching circulating currents.