This study presents a new DC/DC converter with series-connected transformers to achieve zero voltage switching (ZVS) for power switches, less transformer secondary winding and partial ripple current cancellation. Two three-level circuits using the same active switches are operated with interleaved half switching cycle. The voltage stress of all switches is clamped at V in /2. The transformers secondary windings are connected in series to balance the primary side currents. The current-doubler rectifier is adopted on the output side. Thus, the output inductor ripple currents can be partially cancelled each other and the resultant ripple current at the output capacitor is reduced compared with the output ripple current of the centre-tapped rectifier topology. Based on the resonant behaviour by the output capacitance of active switches and the leakage inductance (or external inductance), all power switches are turned on at ZVS. Laboratory experiments with a 1 kW prototype, verifying the effectiveness of the proposed converter, are described.

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This paper presents a new interleaved pulse-width modulation (PWM) boost-flyback converter to achieve power factor correction (PFC) and regulate DC bus voltage. The adopted boost-flyback converter has a high voltage conversion ratio to overcome the limit of conventional boost or buck-boost converter with narrow turn-off period. The proposed converter has wide turn-off period compared with a conventional boost converter. Thus, the higher output voltage can be achieved in the proposed converter. The interleaved PWM can further reduce the input and output ripple currents such that the sizes of inductor and capacitor are reduced. Since boundary conduction mode (BCM) is adopted to achieve power factor correction, power switches are turned on at zero current switching (ZCS) and switching losses are reduced. The circuit configuration, principle operation, system analysis, and design consideration of the proposed converter are presented in detail. Finally, experiments conducted on a laboratory prototype rated at 500W were presented to verify the effectiveness of the converter.