Influence of the connection topology on the performance of lithium-ion battery pack under cell-to-cell parameters variations

In order to meet the energy and power requirements of large-scale battery applications, lithium-ion cells have to be electrically connected by various serial-parallel connection topologies to form battery pack. However, due to the cell-to-cell parameters variations, different connection topologies lead to different performance of the battery pack. Therefore, knowledge of correlations of the connection topology on the performance of battery pack is worth investigating. Based on a simplified analytical circuit model, this paper derives the capacity, voltage, discharge power and energy of the pack with different connection topologies by transformation algorithm. Thus, we use Monte Carlo simulation to quantify the effects of parameters variations on usable capacity and power of the pack under four typical connection topologies under random sampling. The capacity mean and variance expressions of the battery pack with different topologies are obtained. The results show that the battery pack with cell firstly connected in parallel and then assembled in series can better reduce the influence of cell parameters variation, achieve more performance and greatly increase the usable capacity and energy utilization. Moreover, increasing the quantity of serial or parallel connected cells can reduce the discrete coefficients of capacity of the packs. The main conclusions are of great benefit to the battery manufacturer, electric vehicles and energy storage systems applications.