A Variable Tertiary DC-Link Voltage Control for integrated APM in EV Charger Systems Featuring Full ZVS Range

The Auxiliary Power Module (APM) can be topologically merged with the on-board charger (OBC) to form a vehicle charging system (VCS) with enhanced power density. While operationally similar to standalone APMs, circuit variations may result in functional differences, especially in the phase-shift full-bridge (PSFB) converter, where the interaction between magnetizing current and resonant current is critical. This paper, therefore, investigates such a specific VCS topology, functioning as a two-stage isolated DC-DC converter for integrated APM, wherein the PSFB converter functions as the front-end and buck converter serves as the back-end. This configuration, however, faces challenges related to hard-switching under light loads, leading to reduced system efficiency and electromagnetic compatibility (EMC) issues. To address these issues, a variable front-stage output voltage strategy is proposed to achieve full-range ZVS operation, enhancing the VCS’s efficiency in driving mode. Herein, only large signals are utilized for calculation to ensure system robustness and stability across all operational stages. Finally, a 1kW VCS prototype is built to confirm these findings, showcasing a peak efficiency of 94.5% and a notable 7% efficiency improvement under light loads.