模块化多电平换流器子模块拓扑设计及其控制

根据直流故障电流切断位置不同，首先分析基于交流断路器、直流断路器和模块化多电平换流器子模块拓扑的3种故障抑制技术方案及其特点。然后从切断故障电流角度出发，利用双向可控开关对半桥拓扑进行改进设计以抑制直流故障，并与传统半桥子模块相结合构成混合双子模块拓扑以降低单位电平成本和运行损耗。同时研究在闭锁期间混合双子模块内部电容不均衡充电所导致的电容电压不平衡问题及其应对策略。最后在PSCAD/EMTDC中搭建两端仿真模型，对混合双子模块拓扑直流故障抑制特性及电容电压控制策略进行仿真验证。

Design of sub module topologies and their control for modular multilevel converter

Firstly, according to the different cutting off positions of DC link fault current, three possible fault suppressing techniques based on AC circuit breaker, DC circuit breaker and modular multilevel converter sub module topology and their respective features are summarized. Secondly, from the perspective of cutting off the fault current, the double direction controllable switch is used to improve half bridge sub module to achieve DC fault suppression. Subsequently, combined with traditional half bridge sub module, HDSM(Hybrid Double Sub Module) topology is designed to reduce the unit level cost and operating loss. Moreover, the problem of HDSM internal capacitor voltage imbalance caused by the unbalanced charging during blocking and its countermeasures are analyzed. Finally, a two-terminal simulation model is built in PSCAD/EMTDC to verify the effectiveness of HDSM DC link fault suppressing characteristics and capacitor voltage control strategies.