Measurement method and parametric modelling of LiFePO4 cell for SOC estimation in EVs

Spurred evolution in hybrid electric vehicles (HEVs) and electric vehicles (EVs) development, over the last decades, imposed the Li-ion battery (LIB) as the preferred energy storage element. Ever since, the accurate assessment of the LIB state-of-charge (SOC) during the demanding EV operation regimes posed serious challenges. Hence, several methods were developed in order to estimate the available useful charge, ranging from the less robust and straightforward Coulomb Counting to the powerful, nonlinear Kalman Filter variations. The kernel of any effective state-of-charge estimator resides within the employed battery model, mimicking the actual behavior of the part, so that a causal relationship between SOC and other physical quantities (e.g. terminal voltage) emerges. This article depicts a systematic procedure for designing a comprehensive equivalent circuit battery model using readily available tools, such as Matlab/Simulink suite, for a LiFePO4 pouched cell. Also, some key but not obvious aspects concerning the battery modeling approach (i.e. LIB parameters extraction) are pointed throughout the paper.