High step-up resonant push-pull converter with high efficiency

A high-efficient current-fed push-pull converter is proposed for high output voltage applications supplied by low-voltage and high-current sources such as fuel cells and solar cells. The proposed converter conserves inherent advantages of a conventional current-fed push-pull converter such as low input current stress and high-voltage conversion ratio. The converter employs a voltage-doubler rectifier in order to remove the reverse-recovery problem of the output rectifying diodes and to provide much higher voltage conversion ratio. Additionally, by allowing the duty ratio < 0.5, the converter operates in wider input voltage range, and the ripple current of a boost inductor is reduced, compared with the conventional one. Moreover, as the duty ratio approaches 0.5, the ripple of the inductor current moves in close to zero. The operation of the proposed converter is analysed and experimental results obtained from a prototype verify the analysis. The prototype was implemented for an application requiring a 1.5 kW output power, input voltage range varying from 35 to 60 V, and 350 V output voltage. Experiment results show that minimum efficiency at full load is about 95.5%.