HV-Bus-Assisted Flyback Converter With Only One Additional Active Switch for Leakage- Energy Recycling and Full-Range Soft Switching

Abstract This paper proposes an HV-bus-assisted flyback converter (HBAFC) for systems with a common-ground HVDC bus and battery. The HBAFC is supplied directly from the battery and, with only one auxiliary diode connected to the existing HVDC bus, can recycle transformer leakage energy and clamp the main-switch voltage. Replacing the diode with an actively controlled switch establishes the reverse current in the leakage inductance required for ZVS turn-on of the main switch over the full operating range. Since the HBAFC does not depend on the power stage or switching operation of the existing bidirectional converter between the HVDC bus and battery, it operates independently and supports modular expansion to different output voltage and power ratings. The operating principles, steady-state characteristics, device stresses, and ZVS condition are analyzed and discussed in detail. Three 200-W HBAFC modules with 12-, 24-, and 48-V outputs have been built and experimentally tested. The results confirm independent operation, leakage-energy recycling, and main-switch ZVS turn-on. In the active-switch version, the full-load efficiencies of the 12-, 24-, and 48-V modules are 89.6%, 94.2%, and 96.1%, respectively.