A method for simplified modeling and capacity, state of charge, current distribution analysis based on arbitrary topology connection battery pack

摘要

To meet the electric energy requirements of electric vehicles (EVs), the battery cells in power battery pack are normally connected in series and parallel. During the process of battery manufacturing and storage, battery parameters of the same batch and type are inconsistent, which may lead to accelerated aging of power batteries. Because of the change of cell-to-cell parameters, varied battery system topology structure will result in different battery pack characteristics. For power battery pack system design and optimization, it is important to under-stand the relationship among inconsistent parameter distribution, topological connection and battery perfor-mance. The traditional bulk model is based on the external characteristics of the battery pack, ignoring the inconsistency of cell-to-cell parameters. In order to investigate the non-uniform characteristics of battery pack, a simplified modeling method for power battery pack is proposed in this paper, which takes into account the parameter inconsistency of the battery pack and is suitable for power batteries with arbitrary topology. Based on the equivalent circuit model (ECM), a parallel model of two-cells is established and extended to the ECM of arbitrary topology structure battery pack. The analytical solution of the battery model is simplified by s-domain analysis and the transformation of current source and voltage source model. Based on the simplified model of battery pack with arbitrary topology, the 104 times Monte Carlo simulations is used to analyze the capacity distribution, state of charge (SOC) difference and maximum current distribution of the battery pack under different topology structures and parameters. The Monte Carlo simulation solves the problem of complex analytical solution of battery system and greatly improves the simulation speed. The results show that the series connection increases the voltage, but it will reduce the capacity. The parallel connection increases the capacity of battery pack, but it will lead to the increase of SOC inconsistency, maximum current and standard deviation of capacity. This paper provides a theoretical basis for reducing the heterogeneity of battery pack and a reference basis for battery manufacturers.