基于MMC环流模型的通用环流抑制策略

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

模块组合多电平变换器(modular multilevel converter,MMC)的环流直接影响MMC的工作特性。该文推导了MMC环流、桥臂电流和公共直流母线电流之间的数量关系,指出环流是引起公共直流输入/输出功率存在低频脉动的原因。为实现对MMC环流的有效抑制,提出一种基于MMC环流模型的通用环流抑制(universal circulating current suppressing,UCCS)策略,实现原理简单,无需负序坐标变换和相间解耦环节,适用于任意相数的MMC控制,并进行了仿真和实验验证。结果表明,UCCS策略能显著抑制环流中的低频交流脉动分量,消除桥臂电流的畸变,同时可有效抑制公共直流输入/输出功率脉动,有利于MMC系统的稳定可靠运行。

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.