Research On Energy Storage State Estimation And Function Optimization Of Battery Management System For Electric Vehicles

In recent years,with the increasing environmental pollution and the depletion of global oil resources,the characteristics of high energy utilization and no pollution of electric vehicles have attracted the attention of countries all over the world,and they have begun to pay attention to the research and development of new energy electric vehicles.Among many battery pack technologies,lithium-ion batteries not only have excellent performance,but also have a high degree of commercialization,and have gradually become the best choice for electric vehicle energy storage technology.Battery SOC plays an important role in the energy management of electric vehicles.It can optimize the energy utilization efficiency of electric vehicles and improve the capacity and energy utilization of batteries.However,the traditional ampere-hour method and OCV method have problems such as difficulty in determining the initial value,large cumulative error,and long-term rest.During the manufacturing process of lithium-ion batteries,due to differences in raw materials,production processes,charging and discharging,etc.,it is easy to cause overcharge and overdischarge of individual cells,affect the performance of the overall battery pack,and even cause safety problems.In order to realize the accurate estimation of battery SOC and ensure the safe and stable operation of battery packs and monomers,this paper conducts research work in the following three aspects:Firstly,the actual operating conditions of electric vehicles are complex and changeable.As the only power source of lithium-ion batteries,their performance is easily affected by various factors.The various characteristics of lithium-ion batteries are described by using working characteristic parameters such as voltage,capacity,temperature,and internal resistance.The accurate establishment of the equivalent circuit model of lithium-ion battery is not only used to accurately describe the external voltage characteristics,but also can improve the accuracy of SOC.Considering the complexity and amount of calculation in the implementation process,this project adopts the second-order RC equivalent circuit model,uses the existing charging and discharging equipment in the laboratory,builds an HPPC test circuit,and uses the curve fitting method to identify offline parameters and record them.Analyze and verify the parameter identification results by OCV,and analyze and verify the parameter identification results.Secondly,the SOC of lithium-ion cannot be obtained directly,and its accuracy is easily affected by various factors.Aiming at the problem of poor estimation accuracy of open-loop estimation methods such as OCV method and ampere-hour integration method of single lithium-ion batteries,the state-of-charge estimation method based on the second-order RC equivalent circuit model and data fusion is adopted,and opencircuit voltage and other parameters are used to fixing SOC.In the actual working environment of electric vehicles,the SOC estimator established considering the ampere-hour integral method and EKF method cannot guarantee the stability and prediction accuracy of the system.The SOC estimator based on adaptive Kalman filter combined with noise covariance matching technology is effective.Solve the problem that prior noise information has too much influence on the algorithm.Analyze and compare different models using EKF and AEKF to estimate SOC and lithium-ion battery terminal voltage under different working conditions.The results show that the root mean square error of AEKF algorithm estimation is smaller under complex working conditions.Thirdly,there is a problem of inconsistent performance of the single cells in the series battery pack,which can easily affect the service life of the battery pack and reduce the overall available capacity of the battery pack,while the ordinary equalization circuit cannot meet the requirements of fast equalization and high transfer efficiency.Aiming at the problems of large energy loss of the adjacent ratio control strategy and slow balance speed of the most value balance control strategy,considering dividing the battery into the bottom module and the top module for balance control,and taking the SOC as the balance goal,a new bottom level equalization control strategy based on the bidirectional Cuk change circuit is proposed,and the test circuit is built by using Simulink.The results show that it can effectively solve the problems of high energy loss and slow equalization speed.