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 onboard 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 article, 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 zero-voltage switching (ZVS) operation, enhancing the VCS’s efficiency in the driving mode. Herein, only large signals are utilized for calculation to ensure system robustness and stability across all operational stages. Finally, a 1-kW VCS prototype is built to confirm these findings, showcasing a peak efficiency of 94.5% and a notable 7% efficiency improvement under light loads.