Zero-Voltage Switching and Soft-Commutating Two-Transformer Full-Bridge PWM Converter Using the Voltage-Ripple

A zero-voltage switching (ZVS) and soft-commutating two-transformer full-bridge pulsewidth modulation converter using the voltage ripple is proposed in this paper. It is based on the phase-shift full-bridge with series-connected two transformers (TTFB) that act as an output inductor as well as a main transformer. Moreover, the TTFB converter achieves the ZVS of all the switches inherently even at a light load using the energy stored in the magnetizing inductance of each transformer. However, it has several drawbacks such as circulating energy during the freewheeling state, loss of duty cycle, and high voltage stress across the output rectifier diodes. To overcome these drawbacks, the proposed converter employs an output-voltage-doubler, allowing the output rectifier diode to softly commutate with less voltage stress, to reduce the freewheeling interval as well as the circulating energy. The operational principle, technical analysis, and design considerations are described. Finally, the experimental results from a 425 W, 385 V_dc /170 V_dc prototype are presented to confirm the operation, validity, and features of the proposed converter.