Study on an Improved CLLC Converter for Wide Voltage Range Applications

A modified CLLC resonant converter with LC series resonant auxiliary circuit is proposed. The proposed converter is derived by parallel a LC series resonant circuit with the transformer, to make the equivalent magnetizing inductor increase with the switching frequency within the operating range. When operating at unity gain, the LC series resonant branch with high impedance reduces the turn-off current and circulating power, thereby improving the efficiency. The low efficiency of traditional CLLC converters in wide voltage range applications is addressed. Moreover, the converter is modelled based on the extended function description method and the effectiveness of the small-signal model is verified through simulations. Based on the presented small-signal model, the frequency modulation compensator is designed. The enhancement of the overall efficiency in wide voltage applications with the modified bidirectional CLLC DC/DC converter and the controller design had been validated by a 390V-55.5V/800w prototype.