Current distribution of parallel-connected cells in dependence of cell resistance, capacity and number of parallel cells

摘要

Parallel-connection of lithium-ion cells is of increasing research interest, caused by the commercialization of large-scale applications and their needed amount of energy. However, correlations of cell parameters on the current distribution of parallel-connected cells are not given in present literature. This paper provides an insight into the influence of cell resistance and capacity on the current distribution, open circuit voltage (OCV) differences and the corresponding time constants for parallel-connected cells. Cell currents and OCV differences are evaluated via an analytical model for two parallel-connected cells. The system can be described by four characteristic values, what is mathematically shown. The analytical solution and characteristic values are extended to n parallel-connected (np) cells by a transformation of the np equivalent circuit model (ECM) to a corresponding 2p ECM. The models are used in order to investigate the effects of Gaussian distributed cell parameters on the current distribution by Monte Carlo simulations. Thereby, the influence of the number of parallel-connected cells and the product of cell resistance and capacity is examined. Simulations show increasing cell currents with increasing number of parallel-connected cells and an accelerated SoC balance within the logical cell by decreasing product of cell resistance and capacity.