Soft-Switching Current-Fed Push-Pull Converter for 250-W AC Module Applications

In this paper, a soft-switching single-inductor push-pull converter is proposed. A push-pull converter is suitable for low-voltage photovoltaic ac module systems, because the step-up ratio of the high-frequency transformer is high, and the number of primary-side switches is relatively small. However, the conventional push-pull converter does not have high efficiency because of high-switching losses due to hard switching and transformer losses (copper and iron losses) as a result of the high turn ratio of the transformer. In the proposed converter, primary-side switches are turned ON at the zero-voltage switching condition and turned OFF at the zero-current switching condition through parallel resonance between the secondary leakage inductance of the transformer and a resonant capacitor. The proposed push-pull converter decreases the switching loss using soft switching of the primary switches. In addition, the turn ratio of the transformer can be reduced by half using a voltage-doubler of secondary side. The theoretical analysis of the proposed converter is verified by simulation and experimental results.