High Efficiency Resonant Converter with Smooth Frequency Regulation for Wide Input Voltage Applications

Aiming at the problem that the wide voltage gain of traditional LLC resonant converters is limited, a novel high-efficiency resonant converter is proposed. It can maintain the output voltage within a narrow frequency adjustment range in both under-resonance and over-resonance areas. Thus, it adapts to wide input voltage applications without complex control strategies. The paper introduces the proposed topology and its working principle. Also, the fundamental wave equivalent mathematical model is established, the gain expression is deduced and the corresponding characteristics are analyzed. On this basis, the influence of each resonance parameter on the voltage gain is analyzed. Finally, a 500W experimental platform of 200$\sim$400V/4SV is built. The experimental results show that the proposed converter can not only smoothly and quickly adjust a wide input voltage range in the under-resonance and over-resonance frequency bands, but also transmit the fundamental and third harmonics power, which improves the working efficiency, and at the same time has good soft-start and short-circuit current limiting capabilities.