Improved ZVS Three-Level DC-DC Converter With Reduced Circulating Loss

An improved three-level (TL) dc-dc converter is proposed in this paper. The converter contains two transformers. Like the conventional TL dc-dc converter, there are no additional switches on the primary side of the transformer. The rectifier stage is composed of four diodes in the center-tapped rectification. On the primary side of the transformer, the two transformers are connected in series. The middle node of the two transformers is connected to the neutral point of the split flying capacitors. Because it cooperates with the four-diode rectifier stage, the circulating current on the primary side of the transformer decays to zero during the freewheeling period. The zero-voltage switching (ZVS) of the leading switches is determined by energy stored in the output filter inductor, which is similar to the conventional TL converter. The ZVS of the lagging switches is determined by the energy stored in the magnetizing inductor of a transformer, rather than the energy stored in the leakage inductor. The proposed converter can reduce the output filter inductance. Because of the advantages given above, the efficiency of the proposed converter is far better than that of traditional methods. Finally, a 1-kW prototype was built to verify the performance of the proposed converter.