Research On Imbalance Phenomenon Of Vehicle Power Battery Pack And Optimization Of Active Equilibrium Energy Path

It has been a hundred years since the birth of traditional fuel vehicles.Energy and environmental issues are becoming more prominent.Developing new energy vehicles is one of the effective measures to address the problem and is the main focus of support in the national research and development plan.Lithium batteries are a major source of energy for new energy vehicles.As the imbalance caused by the non-uniformity of the energy battery pack has greatly affected the performance of the new energy vehicles,further research on the imbalance phenomenon and balance technology of the power battery pack is crucial.This article focuses on two key issues:analyzing the imbalance phenomenon of power battery packs and formulating balancing strategies for imbalance states,with the aim of formulating corresponding active balancing energy path optimization strategies for different imbalance states,in order to better solve various imbalance problems of battery packs.This article analyzes the imbalance phenomenon,classifies the imbalance states based on the imbalance evaluation indicators,and analyzes appropriate balancing solutions.It builds an equivalent circuit model of the battery.It uses parameter identification methods and DEKF algorithm to estimate the remaining power of the imbalance evaluation indicators,based on the centralized inductive balancing topology,formulate a simple imbalance state balancing strategy for the static state of the battery pack and an optimization strategy based on particle swarm optimization for the complex imbalance state.Propose an optimization strategy based on two-level particle swarm optimization for the complex imbalance state of the hierarchical structure.The simulation results show that the proposed balancing strategies for different imbalance states have good balancing effects,and the optimization algorithm for complex imbalance states can also play a significant optimization role.This paper is mainly divided into four parts:research on battery pack imbalance phenomenon,lithium battery modeling and state estimation,equilibrium topology and equilibrium strategy research,and equilibrium strategy simulation verification.The main work of this paper is as follows:（1）Firstly,the development and research status of battery pack inconsistency research and equalization technology at home and abroad are described,and the causes and effects of battery pack imbalance are analyzed in combination with the characteristics of battery performance.Detailed comparative analysis is conducted and the imbalance evaluation indicators in this article are selected.By analyzing the characteristics of battery pack imbalance,the imbalance status is classified for each individual state within the battery pack,and the most appropriate balancing solution ideas are selected,develop equilibrium effect evaluation indicators based on statistical principles as the basis for subsequent specific research in various aspects.（2）Then,research is conducted on the estimation of the remaining power consumption of the imbalance evaluation index.Realizing the state estimation of lithium batteries is conducive to quantitatively analyzing the imbalance phenomenon and formulating an equilibrium solution.The capacity test,HPPC working condition test and FUDS working condition test were carried out for a certain type of ternary lithium battery.After comparing several common lithium battery models,the second-order RC equivalent circuit model was chosen,and the model parameters were identified online and the results were checked by combining the experimental results.At last,the DEKF algorithm was used to study the SOC and the maximum available capacity Q_premaxestimation algorithm based on the established equivalent circuit model was verified and the results obtained.This demonstrates the high accuracy of the equivalent circuit model,and the algorithm has a good estimating effect on SOC and the maximum Q_premax capacity available.（3）Then we study the equilibrium topology and the equilibrium strategies for different unbalance states.A centralized inductive topology is selected as the balanced topology in this paper,and the working modes of its monomer to group and monomer to monomer are analyzed in detail.Based on this topology,an average value balancing strategy and an optimal value balancing strategy are designed for the simple imbalance state within the battery pack in the static state.A particle swarm optimization strategy based on particle swarm optimization is proposed for complex intra group imbalance states,and the transfer target is determined by calculating an energy transfer matrix.Finally,a double-layer particle swarm optimization strategy is proposed for the hierarchical structure,and a double-layer maximum method balance strategy is constructed for comparison with its subsequent balance effect.（4）Finally,a simulation scheme is established based on an example,and the simulation verification of the three balancing strategies in the group is carried out,and the balancing effects of different methods are systematically compared and analyzed.For the layered structure,the double-layer maximum method equalization strategy and double-layer particle swarm optimization equalization strategy are simulated,and the equalization effects of the two methods are also compared and analyzed.The results show that the proposed balancing strategies for different imbalance states have good balancing effects.On the range and standard deviation indicators representing the degree of consistency,the particle swarm optimization strategy optimizes more than 66%compared to the other two intra group balancing methods,and the two-level particle swarm optimization strategy in a hierarchical structure optimizes more than 80%compared to the two-level maximum method,indicating that the optimization algorithm in complex imbalance states can play a significant optimization role.