Research On Evaluation Indexes Of Lithium Battery Pack Equilibrium Under Different Operating Conditions

With the increasing application of lithium-ion power batteries in various fields,ensuring the safety of lithium batteries and increasing the battery range of battery packs has become a research focus of current lithium battery technologies.At present,researchers have focused on the research of equalization technology in two aspects: the equalization algorithm and the equalization topology.There are few targeted studies on equilibrium indicators,and the equalization index is used as a state parameter to evaluate the degree of inconsistency of the battery pack.Its reasonable choice will be directly Affects the speed and effect of equalization,so the reasonable choice of this indicator is extremely important for the development of equalization technology.The traditional equilibrium index research starts from the characteristics of the equilibrium index itself,ignoring the impact of working conditions on the performance of the equilibrium index.Therefore,this paper analyzes the characteristics of each equilibrium index under different operating conditions,and proposes strategies for applying the equilibrium index under different operating conditions.The reasonable selection of equilibrium indicators provides a reference.The research contents of this article mainly include the following four points:(1)Briefly analyze the causes of inconsistencies in power battery packs and the influencing factors that exacerbate battery pack inconsistencies from the three aspects of lithium battery production,storage,and later use,and design constant current charge and discharge characteristics experiments and variable current simulation tools.In the experiment,inconsistency analysis is performed on battery state parameters such as working voltage,open circuit voltage and state of charge.(2)Analyze the change characteristics and stability of each equilibrium index under different working conditions.Combining the inconsistent manifestations of lithium battery packs and the effects of different equilibrium indicators to characterize the performance differences of single cells,an application strategy of equilibrium indicators under different operating conditions is proposed.(3)Since the SOC and open-circuit voltage equalization indicators cannot be measured directly online,they need to be implemented by online estimation methods.Therefore,this paper based on the unscented Kalman filter algorithm to achieve accurate estimation of the SOC of the single cell,and verify the accuracy of the SOC estimation under custom operating conditions.The neural network is applied to the online estimation of the open-circuit voltage,and an open-circuit voltage on-line estimation model is established in MATLAB to achieve a high-precision online voltage estimation of the open-circuit voltage with a maximum error of 6 mV.(4)Validate the proposed equilibrium index application strategy through experiments.Set up experiments under different working conditions,compare the equalization effect under different equalization index conditions under the same equalization strategy and experimental platform,and use the open-circuit voltage extreme difference after working for 30 minutes to evaluate the equalization index application strategy.The verification results show that the balancing index application strategy proposed in this paper can more accurately characterize the inconsistency of the battery pack.Therefore,the use of appropriate balancing indicators under different operating conditions can further improve the balancing effect of lithium battery packs.The balancing speed is faster and more accurate,which is conducive to extending the battery pack life and improving its use and economic benefits.