# Research on Equalization Strategy of Lithium Battery Pack Based on Multi-Layer Circuit
## 6 Conclusions  
In this study, the balance problem of series lithium battery pack is optimized, a mathematical model of multi-layer balance circuit is established. In order to achieve a safe and fast balance of the battery pack a multi-objective optimization problem is proposed, which takes into account the balancing time, external current, and battery current to optimize the balancing current, maintain the battery current within the allowable range, and reduces battery heating. To improve the computational efficiency and reduce the computational difficulty, a new proposed layered equalization strategy was used to calculate the equalization current of the battery pack in layers, which can realize the fast  
Figure 19: (**a**) case 1 multi-layer equilibrium, (**b**) case 1 adjacent equilibrium, (**c**) case 2 multi-layer equilibrium, (**d**) case 2 adjacent equilibrium, (**e**) case 3 multi-layer equilibrium, (**f**) case 3 adjacent equilibrium, (**g**) case 4 multi-layer equilibrium, (**h**) case 4 adjacent equilibrium.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Equalization Circuit** & **Equilibrium Strategy** & **Equilibrium Time** & \
\begin{tabular}{c} **Maximum** \\ **Current** \\ \end{tabular} &
\begin{tabular}{c} **Current Exceeds** \\ **Limit** \\ \end{tabular} \\ \hline \multirow{2}{*}{Multi-layer equalization circuit} & No strategy & 245.7 s & 5.04 A & Yes \\  & This article strategy & 268.5 s & 3.02 A & No \\ \hline \multirow{2}{*}{Adjacent equalizer circuit} & No strategy & 350.65 s & 4.93 A & Yes \\  & Fuzzy control & Incomplete equalization & 4.72 A & Yes \\  & SOC difference & Incomplete equalization & 4.68 A & Yes \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of equilibrium results.  
calculation of the equalization current. Through theoretical analysis and simulation results, the balance strategy proposed in this study was found to be safer than the multi-layer balance circuit without the balance strategy, and the battery current is kept within the allowable range during the balancing process; the balancing efficiency is 23.55% higher than that of adjacent cells. It was proven that the balancing strategy proposed in this study can quickly and safely achieve the balance of the battery pack.  
Conceptualization, L.W., X.L. ([PERSON]) and C.C.; methodology, X.L. ([PERSON]) and H.L.; software, X.L. ([PERSON]), J.S. and X.L. ([PERSON]); validation, X.L. ([PERSON]), H.L., X.L. ([PERSON]) and L.W.; formal analysis, X.L. ([PERSON]); investigation, X.L. ([PERSON]) and H.L.; resources, X.L. ([PERSON]) and X.L. ([PERSON]); data curation, X.L. ([PERSON]); writing--original draft preparation, X.L. ([PERSON]); writing--review and editing, X.L. ([PERSON]); visualization, H.L.; supervision, L.W. and C.C.; project administration, L.W. and C.C.; funding acquisition, L.W., X.L. ([PERSON]) and C.C. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the National Natural Science Foundation of China Youth Fund, grant number 62003315; ZHONGYUAN Talent Program, grant number ZYCYU202012112; the Applied Basic Research Program of Shanxi Province, grant number 201901D211241; Scientific and Technological Project of Henan Province, grant number 212102210069; 222102210043; and The Young Academic Leaders Support Program of the North University of China, grant number QX202002. Henan International Joint Laboratory of Thermo-Fluid Electro-Chemical System for New Energy Vehicle, grant number Yuke2020-23. Fund of Innovative Education Program for Graduate Students at North China University of Water Resources and Electric Power, China, grading number YK-2021-91.  
Not applicable.  
Data Availability Statement: Data are contained within the article.  
The authors declare no conflict of interest.