Research on zero-sequence circulating current of bidirectional converters

The bidirectional converter device, featuring multiple converters in parallel on both AC and DC sides, employs carrier phase-shifting control. This approach can significantly enhance system capacity and reduce grid current harmonics; however, it also introduces the issue of zero-sequence circulating current. This study first established an equivalent mathematical model of zero-sequence circulating current in a parallel topology bidirectional converter device, analyzed the underlying causes of the zero-sequence circulating current, and proposed corresponding suppression strategies to address the circulating current. To suppress the high-frequency component of the zero-sequence circulating current, a three-phase common-mode reactor was used to increase the zero-sequence circulating current impedance for circulating current suppression. For the low-frequency component, on the basis of the traditional dual closed-loop control strategy for voltage and current, zero-sequence circulating current closed-loop control was incorporated, and the zero-sequence circulating current closed-loop output was added to the original modulation wave to suppress the low-frequency zero-sequence circulating current. Finally, simulation and experimental results demonstrate that this method can effectively suppress the zero-sequence circulating current between parallel modules of the bidirectional converter device.