模块化多电平换流器子模块拓扑仿真分析

Simulation Analysis on Submodule Topology of Modular Multilevel Converter

新型模块化多电平换流器(MMC)在直流输电和电能变换领域得到了广泛的研究与应用。但是,由于子模块采用了半桥型拓扑,在直流侧线路故障时,MMC不具有直流故障自清除能力。文中在不改变现有MMC调制和均压策略的前提下,利用续流二极管反向阻断特性和桥臂模块电容充电效应,设计了改进复合拓扑结构,解决了半桥拓扑中电容单向充电问题。通过分析闭锁时储能电容不同充电路径下交流电压与桥臂等效直流电压关系,定义了反映子模块故障抑制能力的电流抑制系数。根据系统启动过程中不控整流阶段电容电压的不同,设计了自励启动方法。仿真结果验证了启动方法和复合拓扑对直流侧故障电流抑制的有效性。

Despite extensive concern of researchers and wide application in direct current （DC） transmission and energy conversion, the modular multilevel converter （MMC） with a new topology is incapable of clearing the DC link faults because of its semi-bridge submodular topology. An improved hybrid topology utilizing the reverse voltage clamping of forward diodes and capacitor charge effect is designed to solve the unidirectional charge problem without the need to change the control and voltage balancing algorithm. By investigating the different current charge paths, the current blocking coefficient is defined as the ratio between arm equivalent DC voltage and alternating current （AC） voltage magnitude to indicate the blocking effect. The self- excited startup procedure is also designed according to the capacitor voltage in the uncontrollable rectifying process. The effectiveness of this topology is verified by MMC simulation results.