Research on Capacitor-Switching Semi-Full-Bridge Submodule of Modular Multilevel Converter Using Si-IGBT and SiC-MOSFET

This article presents a capacitor-switching semi-full-bridge (CS-SFB) submodule (SM) using Si-IGBT and SiC-MOSFET for a modular multilevel converter (MMC). Compared with the conventional hybrid half-/full-bridge MMC, the CS-SFB MMC has the same dc fault ride-through capability and lower power losses. The conduction loss reduces due to the current sharing phenomenon between Si-IGBTs and SiC-MOSFETs. The switching loss reduces in virtue of the fast recovery characteristic of SiC-diode. The derivation process and working principle of the proposed SM are first introduced. Then, the power loss models are established in the switch, SM, and MMC system levels, respectively. Afterward, the piecewise calculation and simulation results reveal the low-power-loss characteristics of the proposed SM and MMC. Finally, these features are verified by experimental results acquired from a downscaled MMC prototype with Si-IGBTs and SiC-MOSFETs.