5. Analysis and Evaluation of Dual Half-Bridge Cascaded Three-Level DC–DC Converter for Reducing Circulating Current Loss

Three-level (TL) DC–DC converters can meet high input voltage requirement. The isolated TL converters with clamping diodes and flying capacitor are the prevalent TL topologies. However, large circulating current in the primary windings may degrade the efficiency. Although many other TL converters with auxiliary components are proposed and investigated for soft switching, the auxiliary components may increase the weight and size of the converters. The dual half-bridge cascaded (DHBC) TL converter splits the one transformer into two, but no clamping diodes, flying capacitors or other auxiliary components in the primary circuit, which meets the compact size requirement. In order to reduce the circulating current further, an improved dual half-bridge cascaded TL (IDHBC-TL) converter with four rectifier diodes and proper sequence of the transformer windings is introduced in this chapter. Because of the proper sequence of the windings, the circulating currents in the primary side of the transformers decay to zero during the freewheeling period. Although the circulating current is reduced, the primary switches still can achieve zero-voltage switching (ZVS) without any other auxiliary circuits. Besides, the presented converter can reduce the current ripple of the filter inductor, leading to a reduction of the output filter inductance. The evaluation of the good performance in the IDHBC-TL converter is investigated, and the IDHBC-TL converter is compared with some other TL converters. It has compact size and higher efficiency. Lastly, a 1 kW prototype is built to verify the performance of the IDHBC-TL converter.