Diode Clamp Dual Half-Bridge Sub-Module of Modular Multilevel Converter with DC Fault Blocking Capability

The modular multilevel converter (MMC) develops rapidly in HVDC system relying on its various advantages. However, the widely used half-bridge sub-module (HBSM) can't block the DC fault, which reduces the reliability and availability of the MMC-HVDC system. This paper proposes a new topology, diode clamp dual half-bridge sub-module (DCDHB), which comprises of two half-bridge submodules and its clamp circuit. Comparative studies on DC fault blocking capacity and device costs for different topologies are conducted. Compared with the representative topologies like the full-bridge sub-module(FBSM) and series dual sub-module(SDSM), DCDHB can block the DC fault with fewer semiconductor devices. The DC fault blocking capability of DCDHB is verified by MATLAB/Simulink simulation.