Hybrid MMC Based DC Fault Current Limiting Method in VSC-HVDC Transmission System

Modular multilevel converter (MMC) is widely used in DC transmission system, especially in VSC-HVDC power transmission system. Power electronics applied in DC grids is vulnerable to overcurrent after DC faults. DC transmission line faces the problem of fault current suppression. One Hybrid MMC based method is proposed in this paper. By applying certain proportion of full-bridge submodules (FBSMs), the MMC could run at lower voltage during fault at DC side. A two-terminal MMC-HVDC transmission system is built on PSCAD／EMTDC platform to verify the effectiveness of proposed method. The results show that, using this method, in the case of DC fault, the amplitude of fault current can be reduced, and the requirement for the breaking capacity of DCCB could be lowered.