A Star-Channel Modular Multilevel Converter for Zero/Low-Fundamental-Frequency Operation Without Injecting Common-Mode Voltage

This paper proposes a star-channel modular multilevel converter (MMC). It overcomes the zero/low-fundamental-frequency operation issues of conventional MMC while not injecting the common-mode voltage (CMV). The proposed converter is characterized by the cross connections of upper three arms and lower three arms through two sets of star-channel branches. These star-channel branches rebalance the power among three phase legs, resulting in minimized submodule capacitor voltage ripples even at zero/low-fundamental-frequency operation without CMV injection. This feature enables the proposed converter to interface medium/high-voltage DC and variable-frequency AC systems. A 4160-V 1-MW simulation model is performed in MATLAB/Simulink, and a 208-V 5-kW experimental setup is constructed in the lab. Both of the simulation and experimental results verify the feasibility of the proposal.