Equalization method of 'LiCoxNiyMn1-x-yO2-LiFePO4' hybrid battery pack based on charging electric quantity estimation

Battery packs are typically composed of identical cells arranged in series-parallel arrangements, such as LiCoxNiyMn1-x-yO2 battery packs or LiFePO4 battery packs. To fully leverage the advantages of both LiCoxNiyMn1-x-yO2 cells and LiFePO4 cells, manufacturers have proposed an innovative scheme where the two types of cells are connected in series to form a hybrid battery pack. However, the electrical characteristics of the two cells differ significantly. As capacity degradation and self-discharge, the electrical quantity difference between the cells and the configuration of the hybrid battery pack will gradually change. Therefore, a dissipative cell equalization algorithm for the hybrid battery pack based on charging electric quantity estimation is proposed in this paper. The objective of the algorithm is to stabilize the energy output of the hybrid battery pack. We implement the proposed algorithm in simulations, containing a hybrid battery pack model. Dissipation cell equalization algorithm based on charging electric quantity estimation is proved to be effective by comparing the cell electric quantity difference with/without the algorithm. The relationship between cells in the pack with the visualization of equalization is further analyzed. Results demonstrate that closely match the theoretical values achieved through the dissipative equalization strategy after approximately 15 to 20 standard cycles, with a relative difference of no more than 1 % and minimal fluctuations. Therefore, the equalization method can change and recover the electric quantity difference, and achieve the energy stabilization strategy of the hybrid battery pack.