DC Link Voltage Optimization for Efficiency Enhancement of Electric Vehicle Onboard Chargers

Electric vehicles (EVs) are becoming increasingly popular, so it is important to study the efficiency of the EV onboard charging (OBC) systems comprehensively. This paper is focused on the DC link voltage optimization to enhance the overall grid to vehicle (G2V) charging efficiency of the OBC. An EV OBC with ac-dc power factor correction (PFC) and dc-dc dual active bridge (DAB) stages is studied, where the power losses for various converter components are formulated as functions of DC link voltage, battery voltage, and charging power. Afterwards, the optimal DC link voltages corresponding to the minimum total loss at different charging conditions are obtained from theoretical analysis of the circuit for both level-1 and level-2 chargers. A 500 W OBC prototype is experimented in two cases, and the results show that the optimal DC link selection of 345V yields to an overall efficiency improvement of 2% compared to the fixed DC link design (at 400V), while the PFC and DAB stage efficiencies are individually improved and declined by 2.6% and 0.5%, respectively.