Efficient Equalization Strategies For LiFePO₄ Battery Pack With Fusion Of Voltage And SOC Inconsistency

With the rapid development of global economy,energy shortage and environmental protection issues became more serious.As the traditional fuel vehicles use fossil fuels,there are problems such as exhaust pollution and unsustainable development,auto industry have turned their attention to new energy vehicles,because of economic environmental protection,electric vehicle(EVs)have been rapid development.Battery management system,as a key component of EVs,becomes more and more important to ensure the efficient work of EVs in complex road conditions and environments.Due to voltage and power demand,power battery need hundreds and thousands of cells,manufacture process and use-process differences lead to inconsistent between cells,and it will expand,which will greatly affect the available capacity and life of the battery pack,thus equalization system is essential.In addition,the equalization system needs to formulate correct equalization strategy according to SOC state of cell in battery pack.Therefore,cell SOC estimation and equalization system have become the focus of research.In view of the existing problems,such as complexity and low accuracy of SOC inconsistency estimation in battery pack and poor performance of battery pack equalization strategy,this paper studies SOC inconsistency estimation method based on battery pack model,and proposes equalization strategy based on fusion of variables.Specific research work includes:Firstly,the research background and significance of battery and battery management system are summarized,discussed the research status and existing problems of battery pack modeling,SOC estimation method and battery pack equalization system,including hardware circuit and equalization strategySecondly,the equivalent circuit model of the cell is summarized,and the battery experiment and the obtained data are introduced.According to the multi-cell model of the battery pack,the parameters of the battery pack model were identified to get the basic battery pack model and verify the model accuracy.In order to accurately estimate the SOC in the battery pack and reduce the complexity,according to the Li Fe PO4 battery pack,this paper explores the inconsistency of the battery pack and the battery pack model,builds the Simulink battery pack according to the identification parameters,and gives the SOC inconsistency estimation method of the series battery pack.Thirdly,according to the established simulation model of the battery pack,the simulation continues in Simulink.The battery pack created by Simscape electrical components is connected to the equalization system externally,and the exploration of the underlying equalization strategy is carried out,which verifies the feasibility of the duty cycle control method for the underlying equalization strategy.Finally,based on the characteristics of Li Fe PO4 battery,which has a long voltage platform,therefore,SOC is segmenting and battery characteristics are greatly affected by the charge and discharge current.The fuzzy control fusion of SOC variable and voltage variable is used,according to the battery pack SOC and charge-discharge rate as the basis for judgment,and the advantages of the two variables and strategies are fused to achieve an efficient equalization strategy.It not only ensures the consistency of the battery pack,but also compare with voltage-based equalization strategy,battery performance improves4.9%,and compared to SOC-based equalization strategy,it increases 14.9% equalization efficiency of battery pack.