A Three-phase 22kW Soft Switching based Two-stage Onboard Charger

This paper proposes a three-phase 22kW two-stage onboard charger (OBC) which achieves soft switching for both three-phase power factor correction (PFC) and isolated dc-dc converter. The three-phase PFC basically operates as critical conduction mode (CRM) with discontinuous conduction mode. The switching frequency synchronization with DCM operation is applied to reduce the switching frequency range. PCB winding with return path helps to achieve lower profile and better EMI performance. CLLC resonant converter is employed for the isolated dc-dc converter, which has inherent soft switching characteristic. Integrated transformer with controllable leakage inductance and parallel winding with current sharing is used for lower profile and better efficiency. A 22kW two-stage OBC is validated using PCB-embedded module which has better switching performance. The proposed 22kW OBC achieves 96.8% peak efficiency and 4.4kW/L owing to fully planar design.