Analysis, optimized design and adaptive control of a ZCS full-bridge converter without voltage over-stress on the switches

This paper presents the analysis and design of a new current-driven soft-switched full-bridge converter, in which all main switches are zero-current-switched (ZCS), and the switches in a switched-capacitor snubber are zero-voltage-switched (ZVS). For each value of the supply and load, the snubber capacitor is adaptively charged at the minimum necessary value for assuring soft-switching; thus, less resonant energy is circulated. There is no extra voltage stress on the switches. The current through the switches is limited to the input current. A dc analysis led to the derivation of the voltage conversion ratio. The resonant elements of the snubber circuit are optimally designed by trading-off the soft-switching range the duty-cycle loss over a wide supply and load variation. The calculation of the ac small-signal transfer functions allowed for the design of the controller, which was implemented by DSP. A 530 V/15 kV, 5 kW prototype has been built and evaluated.