Hybrid Three-Level and Half-Bridge DC–DC Converter With Reduced Circulating Loss and Output Filter Inductance

A hybrid three-level (TL) and half-bridge (HB) dc-dc converter is proposed in this paper. The TL dc-dc converter and HB converter have their own transformers, respectively. Compared with conventional TL dc-dc converters, the proposed one has no additional switch at the primary side of the transformer, where the TL converter shares the lagging switches with the HB converter. In order to reduce the circulating current in the primary side, a blocking capacitor is used to reset the primary winding current of the TL converter. Moreover, the rectifier stage is composed of four diodes in the center-tap rectification, forcing the circulating current at the primary side to stay zero during the freewheeling period. The magnetizing inductor of the HB transformer can extend the zero voltage switching operation range of the lagging switches even at light loads. Furthermore, the proposed converter can reduce the output filter inductance. Due to the advantages mentioned above, the efficiency of the converter is improved dramatically. The features and design guidelines of the proposed converter are given in the paper. Finally, the performance of the converter is verified by a 1-kW experimental prototype.