A ZCS full-bridge PWM converter with self-adaptable soft-switching snubber energy

A new soft-switching full-bridge current-driven DC-DC converter is proposed for high voltage and high power applications: its power transistors turn-on/off with ZCS, what is suitable for IGBT switches. An active snubber formed by two active switches and one capacitor is inserted in the primary side of the converter. The snubber´s accumulated energy is proportional to the input current, what allows ZCS at a very wide line and load range, by minimizing the required energy: for each value of the input current and load, the snubber´s capacitor is charged only at the minimum voltage necessary for achieving ZCS. Thus, the level of the snubber energy necessary for soft-switching is self-adaptable. The duration of the resonant stages required for achieving the ZCS conditions are very short and independent of the values of the input current and load. No resonant current peaks appear. The experimental results obtained on a 3 kW prototype, built for the input voltage of 250 V and output voltage of 15 kV, confirmed the expected performances.