Resonant converter with fixed frequency control

This paper presents a soft switching DC/DC converter for renewable energy conversion applications. Phase-shifted full-bridge converter with a series resonant tank is adopted to achieve zero voltage switching (ZVS) turn-on for power switches and zero current switching (ZCS) for rectifier diodes within nearly entire load range. Thus the switching losses of power switches and reverse recovery current of rectifier diodes are improved and the circuit efficiency is improved. In order to overcome the drawback of a wide range of switching frequency in the conventional series resonant converters, fixed frequency pulse-width modulation is adopted to regulate the output voltage. In order to reduce and balance the current rating of transformer primary windings for low input voltage applications, the primary and secondary turns of transformers are connected in parallel and series respectively. Full-bridge diode rectifier is adopted at the secondary side to reduce the voltage rating of rectifier diodes for high output voltage applications. Based on the resonant behavior by the output capacitances of MOSFETs and the resonant inductance, all power switches are turned on at ZVS. Finally, experiments based on a scale down prototype are provided to verify the effectiveness of the proposed converter.