Isolated Series-Capacitor-Based Full-Bridge Converter With Reduced Circulating Losses and Wide Soft Switching Range

Aiming at the limitations of traditional full-bridge dc/dc converters, such as, narrow soft switching range, large circulating loss during the freewheeling period, and voltage oscillation on the rectifier diodes, in this paper, a series capacitor-based full-bridge dc/dc converter is presented to reduce the voltage stress of power switches to half of input voltage, and by introducing the asymmetric pulsewidth modulated (APWM) scheme to the proposed converter, zero-voltage switching for all the switches in the proposed converter can be obtained. Moreover, due to the reduced voltage turned-OFF stress for switches, the energy of commutation process for switches is reduced and turned-OFF switching losses can be decreased. Therefore, wide soft switching range for the proposed converter could be achieved on the condition of variable input voltage and load power. Furthermore, a simple auxiliary circuit on the secondary side of the transformer is utilized to clamp the voltage stress of rectifier diodes and voltage oscillation is eliminated. Moreover, during the freewheeling period, the current through the primary side of the transformer can be decay to zero; circulating losses are eliminated and zero current switching for the lagging switches could be achieved. The circuit configuration, operating principle, and relevant analysis results of the proposed converter are analyzed, and a design example is given in this paper. Finally, experimental results from a 400-W 300-380-V/42-V prototype are presented to verify the analysis of the proposed converter.