A Modular Multilevel Resonant DC–DC Converter

A modular multilevel resonant (MMR) dc-dc converter, its modulation, and control are proposed in this article. The MMR converter inherits the desirable features of both the modular multilevel converter and LLC resonant converter, such as high voltage capability, easy fault-tolerant operation, and soft switching. Besides, the MMR can regulate the output voltage over a wide input voltage range with much narrower frequency range compared to conventional resonant converters. By constantly inserting certain number of submodules into the arm according to the input voltage, the resonant tank voltage can be regulated with a relatively constant amplitude regardless of the wide input variation. This modulation technique is acted as a feedforward loop to roughly regulate the output according to the input voltage, and the feedback loop in the control system precisely regulates the output by varying the switching frequency. Simulations on a 200-kW MMR that converts 9-15 kV to 750 V are provided to verify the effectiveness of the proposed topology and control method. Experimental results on an MMR prototype are also given to demonstrate the feasibility.