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 PWM 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) which act as an output inductor as well as a main transformer. 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 in 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, so that it contributes the output rectifier diode to be soft commutated and reduces the freewheeling interval and the circulating energy. The operational principle, theoretical analysis, and design considerations are presented. Also, to confirm the operation, validity, and features of the proposed converter, experimental results from a 425 W, 385 V_dc/170 V_dc prototype are presented