Zero-Voltage and Zero-Current Switching Two-Transformer Full-Bridge Converter Using the Output-Voltage-Doubler

A zero-voltage switching (ZVS) and zero-current switching (ZCS) two-transformer full-bridge PWM converter using the output-voltage-doubler is proposed in this paper. It is based on the phase-shifted full-bridge with series-connected two transformers (TTFB) which act as an output inductor as well as a main transformer. The TTFB converter achieves ZVS for all the switches inherently even at a light load with the use of the energy stored in the magnetizing inductance of each transformer. However, it has several drawbacks such as circulating energy in freewheeling mode, 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 which reduces the circulating current, the freewheeling interval, and the voltage stress across output rectifier diode. 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 420 W, 385 V_dc/210 V_dc prototype are presented