Power Loss Analysis of a Novel Modular Multilevel Converter Based on Semi-full-bridge Sub-module with SiC-MOSFET Switched Capacitors

This paper presents a novel modular multilevel converter (MMC) whose sub-module (SM) is of semi-full bridge structure with SiC-MOSFET switched capacitors. Compared with conventional half-and full-bridge (H FB) hybrid MMC, the proposed capacitor-switching semi-full-bridge (CS-SFB) MMC has the same DC fault ride through capability due to the unchanged positive and negative output voltage levels. The CS-SFB MMC not only possesses the sub-module consistency characteristic similarly as SFB SM, but also it has low power loss characteristic on account of CS technique. The currents of some Si-IGBTs and SiC-MOSFETs are half of the arm current, thus the conduction loss is reduced. Combined with the fast recovery characteristic of SiC-diodes, the switching loss can be reduced simultaneously. The calculation and simulation results based on the verification model show that CS-SFB MMC has better conduction and switching loss characteristic compared with CS-H FB MMC, SFB MMC and H FB MMC.