A Novel 2-RC Equivalent Model Based on the Self-Discharge Effect for Accurate State-Of-Charge Estimation Of Lithium-Ion Batteries

Accurate lithium-ion battery state-of-charge estimation and effective equivalent modeling are important for real-time status monitoring and safety control of lithium-ion batteries. To solve the problem of low accuracy of the second-order RC equivalent model, based on a large number of experimental analyses on the ternary lithium-ion battery, the traditional second-order RC equivalent model was improved, and the self-discharge effect was incorporated into the equivalent model establishment. By measuring the change of the open-circuit voltage of the lithium-ion battery within 30 days in the resting state, the identification of the characteristic parameters of the self-discharge circuit is completed. The experimental results show that, compared with the traditional second-order RC equivalent model, the Self-Discharge-2-RC(SD-2-RC) equivalent model can better simulate the working state of the lithium-ion battery. The maximum error between the analog voltage and the real voltage is less than 0.03V, and its accuracy can be up to 99.3% or more. Based on the accurate establishment of the equivalent model, the Adaptive Extended Kalman filter algorithm is used to estimate the SOC. The algorithm has a fast convergence speed and a good tracking effect. The estimation accuracy can reach more than 96%, and the accurate estimation of the state of charge is realized. This research provides a theoretical basis for the establishment of a more accurate lithium-ion battery equivalent circuit model.