A comparative performance analysis of electrical equivalent circuit models with the hysteresis effect of lithium iron phosphate batteries

Abstract

ABSTRACT This paper aims to develop an equivalent circuit model (ECM) for Lithium Iron Phosphate (LFP) batteries as they have a flat voltage profile and dominant hysteresis behavior compared to other lithium-ion chemistries. Hence, it is challenging to deduce an accurate model to predict the performance of the battery. The model introduces a hysteresis correction factor (HCF) calculated from the capacity test and the R and C parameters for charging and discharging through pulse current test. The state of charge is calculated through Coulomb counting, and over the entire range, the terminal voltage of the model coincides with the experimental voltage. The estimated maximum deviation in the voltage for the existing 2RC model is 45 mV during discharging with a constant C-rate, and for the proposed model, the maximum deviation in the voltage is found to be 30 and 20 mV during discharging and charging, respectively. Further, to increase the accuracy in the estimated voltage, a 3RC model with HCF is found to be the most suitable for LFP batteries. This model reduces the deviation to 10 and 12 mV during discharging and charging, respectively. The performance of the model in MATLAB Simulink is validated with the experimental results through the Dynamic Stress Test (DST) and the Urban Dynamometer Driving Schedule (UDDS). This model reduces the root mean square error (RMSE) in the estimated voltage by 60% under UDDS compared to other existing models.