Online Evaluation And Analysis Of Lithium-ion Battery SOC

With the rapid development of the world,the problem of energy shortage is becoming more and more serious.Oil and coal produce carbon monoxide,carbon dioxide and fine particles in the process of combustion.These pollutants will aggravate the haze weather and pollute the environment seriously.The research and development of electric vehicles can effectively alleviate the environmental pollution and carbon emissions to a certain extent.The research on batteries used in electric vehicles has become a hot topic.Accurate understanding of the state of charge is the basis of battery condition monitoring,fault diagnosis,balance management and life prediction.Lithium ion batteries are used more and more in electric vehicles.It is of practical significance and value to evaluate and study the SOC of lithium ion battery.In this paper,the working characteristics of lithium ion battery are introduced and analyzed firstly,and then the capacity characteristics of lithium battery are analyzed from three aspects:discharge rate,temperature and cycle times.The relationship between discharge efficiency and discharge rate(I.E.current)is also studied.Then,the relationship between discharge rate,temperature,cycle number and capacity factor,discharge efficiency and discharge rate is calibrated by a series of experiments.Then the relationship between open circuit voltage and SOC is studied.Based on the experimental data,the relationship between open circuit voltage and SOC is calibrated according to the electrochemical model.Secondly,the classification of lithium-ion battery model is introduced.Based on the equivalent circuit model and the recursive least square method of forgetting factor,the vector forgetting factor is added.By combining the adaptive single forgetting factor with the vector forgetting factor,the recursive least square method of multiple adaptive forgetting factors is obtained.The adaptive method of forgetting factor is improved to make it more suitable for battery model.Taking lithium iron phosphate battery and ternary lithium battery as research objects,the identification results based on multiple adaptive forgetting factor recursive least square method show that the parameter identification model is suitable for different batteries.In this paper,an adaptive Kalman filter algorithm based on innovation covariance and residuals is used to evaluate lithium battery SOC online,and the coupling relationship between open circuit voltage and SOC is used.The open-circuit voltage calculated by the SOC output at every moment is fed back to the parameter identification system,which makes the SOC output of the model more accurate.Finally,the inconsistency of voltage,capacity and internal resistance of the monomers in the battery pack is analyzed in detail.In this paper,the battery pack in series is taken as the research object,and the definition of the battery pack SOC is given.Because the adaptive Kalman filter algorithm based on innovation covariance and residuals has a large error in the first few hundred steps of SOC estimation,an adaptive Kalman filter algorithm based on fuzzy method is introduced to improve the estimation accuracy of the first few hundred steps.The state equation and observation equation of the series battery are given,the SOC estimation model of the series battery is built,and the accuracy and accuracy of the model are verified by taking the ternary lithium battery in series as the sample cell.