An Isolated Multiport DC-DC Converter for Integrated Electric Vehicle On-Board Charger

This article proposes an integrated on-board charger (IOBC) for electric vehicles (EVs) based on an isolated three-port dc-dc converter. The proposed architecture integrates the on-board charger (OBC) and the auxiliary power module (APM) in a single multiport converter, offering a low component count. The proposed converter is capable of charging high-voltage (HV) and low-voltage (LV) batteries simultaneously, over the entire battery voltage ranges. A three-winding transformer is used to provide galvanic isolation between the converter ports and consequently, power flow is coupled among the three ports. In this article, a boundary condition is derived for the first time and a novel modulation scheme is proposed to regulate the power flow at the HV and LV ports independently, utilizing the converter's 3-degrees-of-freedom (3-DOF). Hence, charging of the HV and LV batteries can be realized similar to dual-active-bridge (DAB) and phase-shifted full-bridge (PSFB) converter, respectively. Results show that all converter semiconductor devices operate with zero-voltage-switching (ZVS) over wide power and voltage range without the need for additional resonant components, due to the proposed 3-DOF selection scheme. A 3.5-kW hardware prototype of the proposed converter is built and tested and key experimental results are presented to verify the converter's theoretical analysis and ZVS operation.