Study On Estimation Of State Of Energy For Lithium-ion Battery

With the increasing number of electric vehicles,the mileage of electric vehicles has become the focus of people’s close attention.Therefore,it is of great significance to accurately estimate the state of energy(SOE)for the lithum-ion battery(LIB).However,there are significant differences in battery energy at different temperature and rates,and the temperature inconsistency of single cell causes changes in the energy efficiency of the battery pack.In response to this phenomenon,the topic has carried out research with the goal of the state of energy for the lithium-ion battery at the current moment.In addition,as the battery life declines,the available energy of the battery will also change.Thence the subject has also conducted an in-depth analysis of the state of energy for the battery in the declining dimension.The specific content is as follows:Firstly,the paper obtains the voltage-time curve of 26650 LIB under different temperature and rate according to the constant current discharge experiment,then based on the voltage-time curve segmental fitting at different temperature,the corresponding function relationship is obtained.Based on the temperature weight interpolation,the corresponding temperature boundary function is selected by dividing the temperature interval,and the voltage curve and the energy relationship curve of the battery at any temperature are obtained.Simultaneously,based on the voltage-time curve of the battery at different temperature,further research is carried out on the influence of cell temperature inconsistency on the energy efficiency for the battery pack,which has made a certain preliminary contribution to the management of battery pack temperature inconsistency.Secondly,in order to obtain the voltage curve and the energy relationship curve at any temperature and rate,this paper conducts further research on the energy of the battery on the basis of the equivalent circuit model.The different the state of energy correspond to the unique open circuit voltage during the discharging process of the battery.The OCV-SOE experiment is used to identify the parameter values at different temperature and rates.Based on the identified parameters,the voltage curve estimation under any temperature or rate is realized by the cubic spline interpolation method.so as to realize the energy estimation under the static constant current working condition;Furthermore,the energy estimation methods based on different static and dynamic working conditions are different.The topic uses online parameter identification based on the Forgetting Factor Recursive Least Squares method to achieve real-time energy estimation,and selects two typical working conditions to verify that the accuracy is higher.Finally,the 18650 battery is studied based on the change of energy under the decay dimension,and the cycle life test experiments and the incremental capacity analysis characteristic tests are carried out,based on the increment capacity curve and increment energy curve the energy change of the battery is compared,and the battery energy is analyzed and estimated according to different peak positions.Meanwhile,an assessment method to characterize the state of health of LIB with energy is carried out based on the perspective of value.