Phase-Shifted Full-Bridge Converter with ZVZCS for Adjustable Output Voltage

Phase-shifted full-bridge DC-DC converter with zero-voltage and zero-current-switching (ZVZCS) is chosen in high voltage and power capacity for high efficiency and power destiny. Leading-leg switches turn on with ZVS, which is easy to realize; lagging-leg switches turn off with ZCS, which is the key point. In this paper, the detail analysis of ZCS achieved with two diodes will be given. When the output voltage should be tuned in a large range, the interval of the current falling down to zero should be considered as resonance of LC, and the voltage of blocking capacitor should be not treated as a constant anymore. Furthermore, to suppress the reverse current and voltage spike of output rectifier diodes, two small saturable inductors are connected with the diodes in series. The method is far more effective than other snubbers, while it will influence the ZCS adversely. A more precise calculation of ZCS is deduced. Simulation and experiment are followed to verify the analysis. A prototype is built with three-phase 380VAC/50Hz input, 100A/50V adjustable output.