Novel multi-terminal MMC-based dc/dc converter for MVDC grid interconnection

Multi-terminal modular multilevel converter (MMC)-based dc/dc converter with the medium-frequency ac-link transformer is an attractive and feasible solution for interconnecting medium-voltage direct-current (MVDC) grids. This study proposes a novel multi-terminal dc/dc converter which features significantly reduced number of components compared with the conventional converter topology. The proposed dc/dc converter is capable of interconnecting multiple MVDC grids with different voltage levels as well as controlling the power flow between them. A combination of sine wave modulation scheme and phase disposition level-shifted pulse-width modulation is developed and employed for voltage balancing and controlling the power flow in the proposed converter. Several simulations, experimental and real-time hardware-in-the-loop case studies are carried out to demonstrate the dynamic response and capacitor voltage balancing capability of the proposed MMC and dc/dc converter under the developed control strategy.