具有直流故障阻断能力的逆阻型模块化多电平换流器

Reverse Blocking Modular Multilevel Converter With DC Fault Blocking Capability

提出一种改进的逆阻型MMC(reverse blocking MMC,RB-MMC)拓扑,其半桥子模块的下管以逆阻型IGBT替代传统的功率器件,并增加了并联旁路吸收回路,用于解决传统MMC的故障阻断能力问题。首先分析了改进的RB-MMC的拓扑和工作原理,在此基础上开展了对改进型RB-MMC的故障阻断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改进型RB-MMC拓扑进行了验证。仿真结果表明,新型RB-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。该文提出的改进型RB-MMC拓扑在高压直流输电系统领域中具有良好的工程应用前景。

This paper proposed an improved reverse blocking modular multilevel converter（RB-MMC） topology for solving the fault blocking issues. Different from the conventional half-bridge sub-modules（HBSM）, two anti-paralleled RB-IGBTs were used as the lower switches for the improved RB-HBSM, which was also featured with an additional bypass snubber circuit. Followed by the analysis of the configuration and 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 RB-MMC topology and the fault protection theory were also verified. Simulation results show that, the improved RB-MMC employs the original control and modulation strategies under the normal operation condition compared with the conventional MMC. Moreover, under fault condition, the improved RB-MMC is able to effectively block the fault current and reduce the consistency requirement of the trigger pulses by adopting the bypass snubber circuits. The proposed improved RB-MMC topology shows good application prospect in the future high voltage direct current（HVDC） transmission system.