A Novel Universal Circulating Current Suppressing Strategy Based on the MMC Circulating Current Model

The performance of modular multilevel converters(MMC) was affected directly by the circulating current.The relation among the circulating current,the leg current and the common dc-bus current was firstly derived,which reveals that the low-order ripple components in the common dc-bus input/output power was caused by the circulating current.Then,a novel universal circulating current suppressing(UCCS) strategy based on the circulating current model was proposed for suppressing the circulating current.Without the second-order negative-sequence coordination transformation and the phase decoupling control,the UCCS strategy was simple in principle,and was suitable for an arbitrary number-phase MMC control.Both the experiment and the simulation verification were carried out,experimental results show that the UCCS strategy can not only effectively suppress the low-order ripple components in both the circulating current and the common dc-bus input/output power,but also improve the leg current distortion,which is benefit for improving the stability and reliability of MMC.