Research On SOC Estimation Of Lithium-ion Power Batteries In High Cold Environments

At present,due to its advantages such as clean energy and environmental friendliness,new energy electric vehicles have become the main development direction of the automotive industry.In new energy vehicles,lithium-ion batteries have the advantages of small size,long cycle life,high energy density,wide operating temperature range,and high open circuit voltage,making them the most important power source for electric vehicles.Therefore,how to effectively monitor and manage lithium-ion batteries has become the primary task.State of Charge(SOC)of lithium-ion batteries refers to the proportion of the current battery capacity of lithium-ion batteries to their rated value,which is of great significance for the safety and range assessment of electric vehicles.The SOC of lithium-ion batteries has a significant dependence on temperature,and most of the existing research is based on SOC estimation methods at room temperature.Therefore,research on SOC estimation methods for lithium-ion batteries under high and cold conditions has its academic value and practical application value.This article is based on the research of various methods for estimating and analyzing the SOC of lithium-ion batteries.The model method is combined with the Adaptive Extended Kalman Filter(AEKF)method to estimate the SOC of lithium-ion batteries in high-cold environments.Firstly,establish a temperature related model for lithium-ion batteries.Choose four different environmental temperatures:-40℃,-30℃,-20℃,and-10℃to conduct charging and discharging experiments on lithium-ion batteries,and record the voltage,current,and temperature during the charging and discharging process.Based on the measurement results,fit the charging and discharging test curve to obtain a second-order RC model for lithium-ion batteries;Aiming at the nonlinearity of lithium-ion battery SOC under low temperature conditions,AEKF filtering and least squares method were used for parameter identification,and a method for predicting lithium-ion battery SOC in high cold environments was designed.According to the standards of the Advanced Battery Association of the United States,four operating conditions,namely DST,UDDS,FUDS,and HPPC,were set up to evaluate the SOC estimation method for lithium-ion batteries under ambient temperatures of-40℃,-30℃,-20℃,and-10℃,respectively.The test results show that this method can not only meet the requirements of predicting the SOC of lithium-ion batteries at a high cold temperature of-40℃,but also achieve an accuracy of±5%.The SOC estimation method for lithium-ion power batteries in high cold environments can provide possibilities for estimating the battery capacity of lithium-ion power batteries in high cold environments.