Equivalent Circuit Evaluation Method of Lithium Polymer Battery Using Bode Plot and Numerical Analysis

This paper proposes an evaluation method for equivalent circuit model of lithium polymer battery (LiPB), which is widely used in the hybrid electric vehicle (HEV), applying the Bode plot and the numerical method. The accurate circuit parameters are determined by numerical analysis and transfer function that is evaluated from the frequency response of LiPB. Generally, the inductive component of battery has an unexpected influence. However, this method takes account of the effect of increased inductive reactance by the high switching frequency. Moreover, the numerical analysis makes the inductive and capacitive components independent of each other, which results in the more accurate circuit parameters of LiPB. The propriety of the evaluation method proposed in this paper is verified by comparison between the voltage-current profiles of battery equipped in the real HEV and that of simulation result using the circuit parameters with respect to the state of charge (SOC) and frequency.