A New Modular Multilevel Converter Topology with Capability of DC Faults Clearing under Blocking and Non-Blocking Mode

The existing DC short-circuit fault current clearing methods have the contradiction between clearing rate and economy. A five-level clamp crossed sub-module (FLCCSM) modular multilevel converter (MMC) topology is proposed, which can achieve rapid clearing of DC fault current at low cost in both blocking and non-blocking modes. The DC fault ride-through processes in the blocking and non-blocking clearing modes are analyzed; the configuration numbers of the capacitors of the sub-modules in the fault current path that meets the fault ride-through conditions in the two clearing modes are deduced; the balanced control of the capacitor inserting in group strategies to improve its voltage equalization effect is proposed. Matlab/Simulink simulation results show that FLCCSM-MMC can quickly clear the DC fault current to zero in the blocking mode, it is mainly used to deal with DC permanent faults. In the non-blocking mode, FLCCSM-MMC can quickly limit the arm current to less than 2 times of the rated value of the bridge arm current, and MMC still has the ability to transmit a certain amount of power, which is more suitable for dealing with DC transient faults, furthermore the capacitors voltages remain balanced before and after the fault. FLCCSM-MMC has the advantages of fast fault current clearing, high reliability, low device cost, and low operating loss. © 2022 Chinese Machine Press. All rights reserved.