Research On Health State Estimation Method Of Automotive Lithium-ion Power Battery

Pure electric vehicles have the advantages of zero emission,low environmental pollution,high energy efficiency,low noise,simpler structure than traditional internal combustion engine vehicles,so pure electric vehicles are the mainstream choice of new energy vehicles at present.As the core power source of new energy vehicles,the cost of lithium-ion power battery accounts for about 40%of the cost of the whole vehicle.For the development of pure electric vehicles,battery technology is one of the core technologies,which affects the range,charging speed,battery performance attenuation and service life at low temperature.In practical application,the performance of lithium-ion battery gradually degrades with the deepening of use degree and time,and finally makes the performance of the battery fail.Therefore,this paper takes ternary lithium ion power battery as the research object,and studies the influencing factors and estimation methods of the health state of lithium ion battery through the combination of relevant experiments and the truth of battery construction simulation.First of all,this paper systematically summarizes the classification,composition and working principle of lithium-ion batteries,and analyzes the main factors that affect the health of batteries,such as temperature,discharge rate and self-discharge.Choose a specific type of lithium ion power battery as the research object,related basic performance test and cycle life test under different conditions,in order to study the attenuation rate of different influence factors on the battery state of health of the impact,the results show that the same temperature conditions to devolve electricity rate,the greater the attenuation rate,the greater the battery health status under the condition of the same discharge rate,the lower the temperature,the faster the battery health attenuation.Secondly,the vehicle model of pure electric vehicle was established by Cruise software and the battery charge and discharge data under different temperature conditions were combined to simulate and analyze the performance of pure electric vehicle,and the influence of different temperature conditions,especially low temperature conditions,on the performance of pure electric vehicle was analyzed.The results show that with the decrease of temperature,the range of electric vehicles and the main power performance are significantly reduced,and the range of electric vehicles under-20℃ is reduced by 40.12%compared with that under 20℃.Furthermore,a second-order RC equivalent circuit model was selected to establish a simulation model of the battery.The parameters of the battery model were identified by the least square method with forgetting factor based on the battery pulse discharge data,and the identification results and model accuracy were verified by combining with the experimental data.The verification results show that the estimation error of the battery is within 0.02V in most of the time,and the maximum error rate is 2.4%.Finally,the joint estimation of SOC and SOH of the battery is carried out by using the dual extended Kalman filter algorithm,and the correctness and accuracy of the algorithm are verified by using the constant current discharge condition and the constant current discharge condition.The verification results show that the maximum estimation error of battery SOC is 1.04%,and the maximum estimation error of battery SOH is 0.17%,which has high accuracy.