Design and implementation of a bidirectional flyback boost/buck integrated converter

A bidirectional flyback boost/buck integrated converter with high conversion ratio is designed and implemented in this paper. When batteries release energy to DC bus, this converter functions like flyback and boost integrated converter, with outputs of flyback and boost converter cascoded to obtain high voltage gain. Energy in leakage inductor is recycled through boost converter, neglecting the need of snubber circuits. When batteries are charged by DC bus, this converter functions like flyback and buck converter working in parallel. Two of the switches are turned on with valley voltage switching, enhancing conversion efficiency. This converter has simple structure and low component counts. Operating principles, steady-state analysis, and component parameter designs are presented. Hardware prototype with four 12 V lead-acid batteries in series and DC bus of 400 V is implemented. Maximum power is 500 W under step-up mode and battery charging current is 2.2 A under step-down mode.