On Optimized Modulation Strategies for Electric Vehicle Integrated On-board Chargers

Integration of the on-board charger (OBC) and auxiliary power module (APM) in electric vehicles (EVs) can reduce the overall weight, volume and cost of the on-board charging system, as well as increase efficiency. This paper proposes optimized modulation strategies for an integrated on-board charger (IOBC) based on triple-active-bridge (TAB) converter. The proposed multiport converter is capable of charging the high-voltage (HV) and low-voltage (LV) batteries simultaneously from the grid. In addition, the HV and LV batteries can also be charged individually from the grid without the need of additional mechanical switches or relays, due to the proposed 5-degrees-of-freedom (DOF) modulation scheme. Detailed loss analysis of TAB is presented for the first time, targeting a simple and accurate estimation of the converter losses. Furthermore, four optimization schemes are proposed aiming to improve the performance of the integrated charger, including reduction of the converter total loss and zero-voltage-switching (ZVS) turn-on for all converter devices. A constant-current/constant-voltage (CC/CV) charging scheme is considered for both HV and LV batteries and the results of the optimization schemes are evaluated using a 4.3kW experimental prototype, while the measured converter efficiency with the proposed optimization schemes reaches 96.1% at nominal power levels.