A Step-Down Resonant Modular Multilevel DC/DC Converter With Extendable ZVS Range Based on Asymmetric Triangular Current

In this article, a new step-down resonant modular multilevel dc/dc converter is proposed for medium-voltage applications. The proposed converter is derived from the combination of the modular multilevel converter (MMC) and resonant converter with a passive auxiliary circuit. It can achieve zero voltage switching (ZVS) over a wide input voltage range for all switches compared with the conventional dc/dc MMC. Specifically, the asymmetric triangular compensating current provided by the passive auxiliary circuit is first introduced to flow into the bridge arms. Then, the current bias caused by the MMC structure is eliminated in the lower side switches of the submodules to achieve ZVS. Moreover, asymmetrical pulsewidth modulation is applied to double the equivalent switching frequency and obtain a high step-down ratio. In this way, the resonant current is reduced, and the conversion efficiency is improved. Besides, the simulation and experimental results of the prototype are presented to demonstrate the viability of the proposed converter. The results convincingly verify the ability of the proposed converter to offer ZVS for all the switches over a wide input voltagerange.