A Si/SiC Hybrid Full-Bridge Submodule for Modular Multilevel Converter With its Control Scheme

Abstract

Due to the high dc voltage utilization and capability of dc fault blocking, the full-bridge submodule-based modular multilevel converter (FBSM-MMC) becomes a prevalent topology for medium voltage high power applications. However, using the Si IGBT for each FBSM can induce high switching loss while the SiC MOSFET suffers from high cost because of limitations of fabrication technologies. To address this issue, a hybrid FBSM consisting of both SiC MOSFET and Si IGBT is studied in this article. In addition, an optimal control scheme is proposed, which adjusts the current conducting path of the FBSM and concentrates the high-frequency switching actions into the SiC module. The proposed control scheme only modifies the submodule (SM) level switching and has good compatibility with the existing MMC modulation schemes. Compared with the MMC solely formed by SiC MOSFET, the hybrid SM has similar switching loss and better performance in terms of conduction loss and cost. The experimental results prove the validity of the proposed topology and control scheme, and the further loss and cost analysis verifies that the Si/SiC hybrid FBSM can reduce the loss by 16.3% and save the device cost by 41.0% compared with the SiC FBSM.