Analytical model of the current distribution of parallel-connected battery cells and strings

摘要

The parallel-connection of lithium-ion cells and strings is of increasing research interest, mainly due to the energy and power demands of large-scale applications, e.g. electric vehicles (EV). For battery systems an accurate estimation of the current distribution within these parallel configurations is crucial for optimal operation and system design. The present paper provides an analytical model for the current distribution of cells and strings connected in parallel. Eight characteristic values are determined, fully describing these systems. These characteristic values are used to investigate the impacts of cell resistance and capacity distributions on maximum currents, open circuit voltage (OCV) and state of charge (SoC) differences within the parallel-connected cells and strings. It is found, that maximum cell currents and SoC differences within parallel-connected cells increase almost logarithmically with the number of parallel-and serial-connected cells. A linear correlation of these values to the related standard deviation of cell's resistance and capacity is shown by Monte Carlo simulations. Maximum string currents decrease by square root with the number of parallel-and serial-connected cells, due to statistical averaging, which cause a square root correlation of the related standard deviation to the number of parallel-and serial-connected cells.