一种具有直流故障限流能力的模块化多电平换流器

为解决传统半桥型模块化多电平换流器(MMC)无法限制直流故障电流的问题,提出一种改进型子模块的MMC拓扑。与传统半桥型子模块拓扑不同,交流输出端口增加了阻断IGBT及其旁路吸收回路。本文首先分析改进型子模块的工作原理,在此基础上开展基于该子模块的MMC的故障限流机理及其主要功率开关器件的电气应力的研究,并通过仿真算例对所提出的拓扑进行了验证。仿真结果表明基于改进型子模块的MMC拓扑在原有正常模式下不需要改变控制策略与调制策略,而在故障阶段能够迅速实现故障电流阻断效果,通过引入旁路吸收回路,进一步降低了对电路触发脉冲一致性的要求,因此在未来高压直流输电系统领域具有良好的工程应用前景。

A Novel Modular Multilevel Converter with DC Fault Current Limiting Capability

In view of DC fault current isolation deficiency for the conventional half-bridge sub- modules (HBSM) based modular multilevel converter (MMC), a novel topology of improved sub-module based MMC is proposed. Different from HBSM, an extra IGBT device together with its bypass snubber circuit are arranged in the AC output port of the improved sub-module. Followed by the analysis of the operation principles, detailed study of the fault current blocking mechanism and the electrical stress of the key power switches were carried out. Moreover, the feasibility of the proposed improved sub-module based MMC and the fault protection theory were also verified. Simulation results show that, the proposed MMC employs the original control and modulation strategies under the normal operation condition compared with the conventional MMC. Moreover, under fault condition, the improved sub-module based MMC is able to effectively block the fault current and reduce the consistency requirement of the trigger pulses by adopting the bypass snubber circuits. Thus it shows good application prospect in the future HVDC transmission system.