An Improved Half-and-full-bridge MMC with DC Fault Blocking Capability

The modular multilevel converter (MMC) is a promising topology in the field of DC distribution system. However, MMCs are vulnerable to the DC-line short-circuit faults. In this paper, an improved half-and-full-bridge MMC (IHF-MMC) topology is proposed. The transferring path of fault current in bridge arm is composed of a thyristor branch and current-transferring branch; on the other hand, the upper arm of phase C adopts unipolar-voltage full-bridge submodules instead of half-bridge submodules to absorb fault energy. After the DC fault occurs, the fault current is transferred to the upper arm of phase C, and then interrupted by the submodules through sequential coordination of two additional branches. The operation principle in different fault stages is analyzed in detail in this paper, and a ± 10kV/2.5MW simulation model is built in MATLAB/Simulink to verify the feasibility and effectiveness of the proposed topology.