A novel T-type half-bridge cell for modular multilevel converter with DC fault blocking capability

The Modular Multilevel Converter (MMC) is very suitable for high-power applications such as High-Voltage Direct Current (HVDC) transmission system. However, the DC fault vulnerability seriously constrains the conventional Half-Bridge based submodule (HBSM) of MMC, while the Full-Bridge based SM (FBSM) and Clamp Double based SM (CDSM) with DC fault blocking capability greatly increase the costs. This paper presents a novel T-Type Half-Bridge based SM (T
²
HBSM) topology that is capable of blocking DC fault current and separating the AC grid from the DC fault point instantly, and it can rebuild the DC link voltage to get the MMC-HVDC back to normal immediately after the fault is clear. More significantly, the proposed T
²
HBSM topology saves one diode and utilizes the same number of switches in comparison with the CDSM. The simulation results in PSCAD/EMTDC demonstrate the feasibility of the proposed T
²
HBSM topology.