A high efficiency hybrid resonant PWM zero-voltage-switching full-bridge DC-DC converter for electric vehicle battery chargers

This paper presents a high-efficiency zero-voltage-switching (ZVS) dc-dc converter combing resonant and pulse-width-modulation (PWM) power conversions for electric vehicle battery chargers. A half-bridge LLC circuit, which operates at series resonant frequency, shares the lagging-leg with a phase-shift-full-bridge (PSFB) dc-dc circuit to guarantee ZVS of the lagging-leg switches of the full bridge from zero to full load. A secondary-side hybrid-switching circuit, which is formed by the leakage inductance, output inductor of the PSFB dc-dc circuit, a small additional resonant capacitor and two additional diodes, is incorporated at the secondary side of the PSFB dc-dc circuit. With the hybrid-switching circuit providing a clamp path, the voltage overshoots that arise during the turn-off of the rectifier diodes are eliminated and the voltage stress of bridge rectifier is clamped to the minimal achievable value, which is equal to secondary-reflected input voltage of the transformer. The sum of the output voltage of LLC resonant circuit and the resonant capacitor voltage of the hybrid-switching circuit is applied between the bridge rectifier and the output inductor of the PSFB dc-dc circuit during the freewheeling phases. As a result, the primary-side circulating current of the PSFB dc-dc circuit is instantly reset to zero achieving minimized circulating losses. The experimental results based on a 4 kW prototype circuit show 98.6% peak efficiency and high efficiency over wide load and output voltage ranges.