Simulation of Factor on SOC Inconsistency within a Series‐Connected Lithium‐Ion Battery Pack

Abstract

This paper outlines a new simulation approach to study the effect of factors on the state of charge (SOC) consistency of Li‐ion battery packs. The proposed method is based on a system model and the Monte Carlo method. The system model includes 100 serial connected equivalent circuit models and their respective parameters. This paper divides the internal and external factors into two categories: independent factors such as internal resistance, capacity, Coulombic efficiency, leakage current, and comprehensive factors related to temperature. The Monte Carlo method simulates the differences and distribution of independent factors among cells. Temperature‐dependent factors are modeled with empirical formulas. Simulation results show that the main factors affecting SOC consistency are differences in battery temperature, leakage current, and Coulombic efficiency. Meanwhile, slight differences in capacity and internal resistance have little effect on SOC inconsistency. Furthermore, this paper demonstrates the effectiveness of the system model.

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“…Lithium‐ion batteries are widely used as power sources for new energy vehicles due to their high energy density, high power density, and long service life 1,2 . However, it usually requires hundreds of battery cells in series and parallel to meet the requirements of pure electric vehicles for mileage and voltage 3 . The differences caused by the initial production process will be continuously amplified in the subsequent use process; temperature, vibration, and mechanical stress can also affect the performance of the battery, resulting in inconsistency failure of battery cells, seriously affecting battery life, and even affecting vehicle safety 4,5 .…”

“…1,2 However, it usually requires hundreds of battery cells in series and parallel to meet the requirements of pure electric vehicles for mileage and voltage. 3 The differences caused by the initial production process will be continuously amplified in the subsequent use process; temperature, vibration, and mechanical stress can also affect the performance of the battery, resulting in inconsistency failure of battery cells, seriously affecting battery life, and even affecting vehicle safety. 4,5 The inconsistency of the battery cell has great harm, in a series module, there is a short board effect in the charging and discharging process of the battery pack, 6 that is, the battery cell with the smallest capacities determines the maximum capacity of the whole battery pack, which leads to the waste of the remaining battery capacity.…”