Wide-Range Mode Variable Strategy Design and Switching Process Optimization for LLC Resonant Converter

In response to the demand for new energy applications and wide-range DC/DC converters, this study focuses on the LLC resonant converter. The traditional LLC working range is not wide enough, so this paper investigates variable mode control to increase the LLC working range without changing the topology. Different control strategies are selected for different modes, and simulation studies are conducted on variable mode control strategies such as full-bridge frequency conversion, full-bridge phase shifting, and half-bridge frequency conversion. The LLC operates in full-bridge frequency conversion mode at low input voltage, half-bridge frequency conversion mode at high input voltage, and full-bridge phase shifting mode at intermediate voltage. The transient process of mode switching is optimized to greatly improve the stability of the converter and reduce voltage fluctuations. Based on the simulation and analysis, the system design of software and hardware is completed, an LLC resonant converter prototype is made, and experimental verification is carried out, confirming the effectiveness of the variable mode strategy.