The evolution and variation of sub-module topologies with DC-fault current clearing capability in MMC-HVDC

The modular multilevel converter (MMC) is a competitive candidate for VSC-HVDC systems. However, the conventional HB-MMC can't block dc link fault current because of the freewheeling effect of diodes. To solve this problem, researchers proposed an account of sub-modules (SMs) with DC-fault current clearing capability. This paper summarizes the 2 basic criteria and provides a comprehensive review of the current SMs' evolution and variation. It also provides a comparative performance evaluation based on DC-fault current clearing capability, operation region, devices cost and power loss. Furthermore, this paper proposed or improved some novel SMs with DC-fault current clearing capability, among which AFB-CCDSM is the main contribution.