Efficiency optimization design of LLC resonant converter for battery charging

LLC resonant converter has the problem of low light load efficiency in electric vehicle charging applications. This paper presents an efficiency optimiz ation design approach for the resonant tank of the LLC converter. The switching loss characteristics under light load conditions are analysed. In the premise of not increasing the complexity of circuit and control, a resonant tank design scheme with minimizing capacitance is proposed. Finally, the design method is verified by experimental results of a 2kW LLC resonant DC/DC converter prototype. With 690V DC input voltage and 75–150V DC output voltage, the comprehensive efficiency of the prototype is up to 93.7%.