Design Consideration for CLLC Converter with High Power and Wide Gain Range

CLLC resonant converter can achieve zero voltage switching (ZVS) turn-on and low current turn-off for the primary side, both zero current switching (ZCS) and ZVS for the secondary side switches, which makes it a great candidate for today's high-frequency, high-efficiency applications. However, for high power applications like electrical vehicle (EV) charger, photovoltaic (PV) power station, energy storage, and railway auxiliary power supply applications, the wide input and/or output voltage range is usually a challenge for resonant converters. Besides, the influence of the secondary-side devices' junction caps to commutation is no longer negligible, but rarely analyzed in literature. In this paper, a control strategy of CLLC converter to boost the output voltage is reviewed. The design of magnetic component, an integrated transformer, is introduced. The process of conventional commutation strategy is analyzed for the cases where the secondary side junction caps are comparable to the primary side ones. Then another commutation strategy is compared, which could reduce the circulating energy by half. Finally, a 100 kHz 30 kW SiC based CLLC converter prototype verifies the proposed design and achieves a peak efficiency higher than 99%.