A Nonlinear Open Circuit Voltage Representation Enabling State of Charge Estimation at the Voltage Plateau Region of LiFePO4 Battery

Abstract

This study proposes a nonlinear representation of the open circuit voltage curve for the state of charge estimation of LiFePO4 battery cell. The proposed open circuit voltage representation is devised by dividing the linear term and nonlinear term of given curve shape. The advantage of the proposed method is that by establishing nonlinear battery cell model, the state of charge can be estimated even if there exists voltage plateau in the open circuit voltage curve. The conventional linearized method cannot estimate the SOC in such area. The effectiveness of the proposed method was verified through simulation with virtual battery cell having wide voltage plateau area in open circuit voltage curve.