Due to the low voltage and capacity of the cells, they must be connected in series and parallel to form a battery pack to meet the application requirements. After forming a battery pack, the inevitable inconsistency between the cells will have a serious impact on its energy utilization and cycle life, and even bring safety hazards , .
This basic principle of series and parallel can be extended to any numbers you wish to create. The diagram below shows the basic principles. In most pack designs the cells are connected in parallel blocks (when P is greater than 1) and then in series. This is an important factor in managing the battery configuration.
Both of these designs have strengths and weaknesses. Hence both have places where they are optimal. Parallel and then series will be the lowest cost, but least flexible. Series and then parallel gives flexibility and redundancy and hence is often found in large battery packs.
The m series battery pack in parallel are named P 1, P 2 …, P m. The n cells and 2 n + 2 MOSFETs in each series battery pack are named B x1, B x2, …, B xn and S x0, S x1, …, S x(2n+1), where x is the serial number of the parallel battery pack (x = 1, 2, …, m). The inductor is named L. Fig. 1.
The 3p3s battery pack is quite simple to visualise. Here we see the 9 cells with connections made to bring them together in parallel and then 3 rows connected in series. This basic principle of series and parallel can be extended to any numbers you wish to create. The diagram below shows the basic principles.
7. Conclusion An active equalization method for series-parallel battery pack based on an inductor is proposed, which has the features of simple structure and low cost, and can realize the equalization between any cell in the series-parallel battery pack.