High Frequency High Power Density Multi-Cell Transformer-Coupled Input-Series-Output-Parallel (ISOP) Double Clamp ZVS Flyback Converter

Double-clamp zero-voltage-switching (DCZVS) fullbridge flyback converter is one of the most attractive solutions for high power density applications with wide input range, because of its features of primary side regulation (PSR) and excellent softswitching. By analyzing the ZVS process and the maximum output power at maximum flux, this paper reveals that the dead-time is one of the key parameters to restrict the output power of the DCZVS converter at high switching frequency. Then, the multicell transformer-coupled input-series-output-parallel (ISOP) structure is proposed in this paper to shorten the dead-time so as to improve the output power of the DCZVS converter, which does not increase the size of the transformer. In the multi-cell converters, the number of cells and the transformer design are also discussed. Finally, A DCZVS prototype with two transformercoupled ISOP cells is built up to validate the design, which achieves a wide input range of 160V-420V and realizes a 28V/20A output with a power density of 1203 W/inch3 and a peak efficiency of 93.69%. Compared with the original DCZVS converter, the proposed two-cell DCZVS converter achieves a 15% increase in power density with the same transformer size and maximum flux.