基于模块化多电平变换器的负序电流补偿系统研究

针对三相负载不平衡引起的负序电流,提出了基于模块化多电平变换器MMC(modular multilevel converter)进行补偿的方案,讨论了其工作特性,提出了相应的控制策略。首先,通过把三相不平衡负载等效为平衡负载的方法,推导出对补偿系统控制的基本要求,明确了补偿的基本原理;然后,分析了补偿系统输入功率特性,提出了MMC用于负序补偿时的等效模型,并分析了环流及电容电压的波动特性,指出三相电容电压之和必定存在二次谐波波动;引入正负序坐标系分离控制的控制策略;最后通过仿真和实验验证了文中提出的结论和控制策略。

Study of Negative Current Compensation System Based on Modular Multilevel Converter

According to negative currents causing by imbalance loads, a compensation strategy based on the modular multilevel converter is proposed in this paper. The system with imbalanced three phase loads is equivalent to the one with balanced loads but imbalanced power supplies, which indicates the demand to the compensation system. The input power characteristics of the compensation system are analyzed, and the equivalent model of the MMC is presented, and using this model, the fluctuant of the module capacitors and the circulating currents are analyzed, which results there must be second harmonic in the average voltage of the three phase capacitors. And then, the control strategy with dependent positive and negative controller is proposed and the delay signal cancellation method is used to separate the positive and negative currents. Finally, the simulation and experiment results verify the conclusions and the validity of the mentioned control strategy.