Modeling and control of circulating current in parallel three-phase PWM converters

When we directly connect three-phase converters in parallel, interactions may occur between converters, in which circulating current is one of the major concerns of them. Though many papers have addressed this issue, however, most of the existed strategies have not good steady performance and until now there is not a control strategy with true redundancy. In this paper, firstly, a novel model of circulating current based on space-vector modulation (SVM) strategy is established, and then the circulating current is analyzed more in detail, and the existed control strategies are analyzed based on this model and their disadvantages are discussed. Finally, two novel decentralized controllers are presented and their effectiveness is examined. The key feature of the proposed strategies is that the control scheme of every converter is identical and self-dependent, so that true redundancy is achieved. Furthermore, the operation performance with the proposed strategies is also improved, especially while the voltage modulation ratio is large. Experimental results are provided to verify the performance of the proposed controllers.