Charge/Discharge Simulation Models of LiFePO4 Cells in MATLAB/Simulink

Abstract

Lithium (Li) cells find widespread applications, particularly in electric vehicles their dynamic characteristics are often represented through equivalent circuit models. In this study, two different second-order equivalent circuit models of LiFePO4 cells are modeled and simulated in MATLAB/Simulink. The first model exhibits capacity changes based on drawn current, while the second assumes constant capacity. The analysis of the simulations results focuses on key parameters such as State of Charge (SOC), Open Circuit Voltage (OCV), and terminal voltage (VT). Comparative evaluations between the first and second cell models utilize formulas derived from prior experimental cell studies. Specifically, a 0.0155% variance in SOC, a 0.00003% difference in OCV, and a 0.00003% distinction in VT were observed between the two models during discharge. A similar assessment during charging observed an error of 0.0447% in SOC, 0.00007% in OCV, and 0.00003% in VT. Furthermore, the discharge process in the first model demonstrates lower SOC, OCV, and VT values, contrasting with higher values during charging. Despite these variances, the study concludes that both models yield similar results, establishing them as viable references for equivalent circuit representations of Lithium cells.