A ZCS full-bridge converter without voltage over-stress on the switches

A current-driven soft-switched full-bridge converter is presented. It contains a snubber formed by a switched-capacitor circuit and a resonant inductor, connected in the primary side. The transformer leakage inductance is used as a part of the resonant circuit. All the main switches are turned-on/off with zero-current-switching (ZCS), and the switches in the snubber are zero-voltage-switched (ZVS). The snubber capacitor voltage is adaptively controlled: for each actual value of the input/load current, the capacitor is charged to the minimum resonant energy necessary for assuring the soft-switching, thus reducing to minimum the circulated energy. There is no extra voltage stress on the switches. All the elements are submitted to the same voltages/currents as their counterparts in a hard-switching full-bridge converter, keeping the conduction losses to minimum. A 530 V/15 kV, 5 kW prototype was built. The experimental results confirmed the theoretical predictions, the proposed soft-switching method resulting in an increase of the conversion efficiency.