An MMC Topology Based on Unidirectional Current H-Bridge Submodule With Active Circulating Current Injection

This study proposed a novel modular multilevel converter (MMC) based on unidirectional current H-bridge submodule (UCH-SM) with active circulating current injection (ACCI). Under the premise of keeping the arm current unidirectional, the UCH-SM was developed by optimizing the full-bridge submodule (FBSM). Although the number of required switching devices of the UCH-SM-based MMC (UCH-MMC) is nearly half of that of FBSM-based MMC (FB-MMC), the advantages of the FB-MMC, such as the dc fault blocking and bidirectional dc-link voltage capabilities, were preserved. The proposed ACCI technique can help keep the arm current unidirectional and reduce the overall semiconductor usage. The parameter design method for keeping the arm current unidirectional and the characteristics of the UCH-MMC with ACCI were also analyzed. The control schemes of the UCH-MMC for the dc-link voltage control and dc-link current control modes were presented. Simulation and experimental results were presented to verify the feasibility and characteristics of the proposed UCH-MMC.