Fixed-Frequency K+d Modulation of Modular Multilevel Resonant DC-DC Converters for Output Voltage Overshoot Optimization

Modular Multilevel Resonant DC-DC Converters (MMRDCs) are emerging as a competitive solution for medium wide input voltage - low voltage (MV-LV) conversion, yet they often encounter output voltage overshoot when submodules (SMs) insert or extract. In this article, a novel K+D control scheme of MMRDCs is proposed, which combines both inserted submodule number K and adjusting width D . Output voltage overshoot could be greatly suppressed and soft switching characteristics could also be improved enormously based on the proposed K+D modulation strategy. The design of magnetic components would benefit from fixed-frequency control. Continuous DC voltage gain is analyzed which could effectively simplify the control loop. Simulations on a 200kW MMRDC that converts 9 kVâ18kV to 750V have been presented to verify the effectiveness of theoretical analysis and control strategies. Experimental results from a prototype are also provided to demonstrate its feasibility.