Adaptive Loss Reduction Charging Strategy Considering Variation of Internal Impedance of Lithium-Ion Polymer Batteries in Electric Vehicle Charging Systems

This paper presents a charging strategy to minimize losses in a lithium-ion polymer battery for an electric vehicle. The proposed charging method which considers the variation of battery internal impedance according to state of charge and C-rate significantly reduces charging losses. Experiment results for a cell prove that the proposed charging method reduces loss by 41.9 % compared to a conventional constant-current charging. Moreover, a 3.3 kW prototype on-board charger is built to investigate the entire reduction of losses in an electric vehicle charging system which includes a 12 kWh battery pack considering capacity deviation. Additionally, the feasibility of the proposed charging strategy is examined according to the charger capacity, and it is shown that the effect is enhanced with increasing charger capacity. It is also revealed that the loss reduction due to the proposed strategy is equivalent to an improved efficiency of 3.35% on a 52.8 kW charger with an average efficiency of 94.49%.