Trapezoidal Current Modulation for a Compact DC Modular Multilevel Converter With ZVS of Submodules and ZCS of Voltage-Balancing Circuits

In this letter, a trapezoidal current modulation is proposed for a compact dc-dc modular multilevel converter with reduced submodule (SM) number and magnetic integration. The arm currents are shaped to fulfill the zero-voltage-switching conditions for all the SMs. Then, the diode-inductor (D-L) circuits between the adjacent SMs are further introduced to cooperate with the proposed modulation; hence, the SM capacitor voltages could be balanced without sensors and sorting algorithm. Besides, the diodes in the D-L circuits could also achieve zero-current switching. Such a full soft-switching operation significantly contributes to the system volume reduction. The proposed method is verified by both simulation and experiment, and under steady-state, transient state, and D-L circuit broken situations.