Lithium-ion Battery Security Guaranteeing Method Study Based on the State of Charge Estimation

[Purpose] The security guaranteeing method for the lithium-ion battery is studied and a novel state of charge (SOC) estimation method is proposed based on the Kalman filtering (KF) thought, aiming to guarantee its safety in the power supply application of electric vehicles (EVs). In this study, there are several parts that have been studied to realize the protection of the lithium-ion battery during its whole life period. Firstly, the core parameters for the working state estimation of the lithium-ion battery is studied and the methods for the state of charge estimation are analyzed. Secondly, the working state of the lithium-ion battery is estimated by the integrated application of the state of charge estimation methods. Then, the estimation model is designed and realized based on the estimation principle. At last, this method and model is proved by the experimental analysis. In the experiments, the main operating temperature varies between 26.84 degrees C and 33.16 degrees C, with an average value of 30 degrees C. The average value of the Coulomb efficiency is about 0.97 and all above 0.95. The average value of the battery capacity is approximately 45.08Ah. When the SOC actual initial value is 0.8 and the test initial forecast value is 0.6, the estimation can track the actual value in less than 5 seconds and has high accuracy. The error covariance value is smaller than 3.5x10(-6) and decreases rapidly as time goes. This study can achieve the working state estimation of the lithium-ion battery, which can guarantee its safety effectively in the power supply applications.