A Self-Calibration SOC Estimation Method for Lithium-Ion Battery

Abstract

Accurate state of charge (SOC) estimation is essential for the battery management system (BMS). In engineering, inappropriate selection of equivalent circuit model (ECM) and model parameters is common for lithium-ion batteries. It can result in systematic errors (i.e., modeling errors) in the state-space equation, thus affecting the SOC estimation accuracy. Aiming at that, this paper proposes a self-calibration method to enhance SOC estimation. In the method, a novel state-space equation containing an unknown systematic error term is developed based on the Thevenin model. A self-calibration unscented Kalman filter (SC-UKF) algorithm is then introduced for recursive SOC estimation. The algorithm can automatically recognize and calibrate the unknown systematic error in the state equation, while also reducing the random noise effect through data fusion with the measurement equation. Test results demonstrate that the method can effectively correct the Thevenin modeling error and improve SOC estimation accuracy. Furthermore, the proposed method is computationally simple and convenient for engineering applications without increasing model complexity.INDEX TERMS lithium-ion battery, state of charge, equivalent circuit model, systematic error, selfcalibration, unscented Kalman filter.

On Controlling the Lithium-ion Battery Charging

“…For estimating the battery SoC, the coulomb counting method is used. It integrates the battery's current with time to calculate SOC, which is less complicated method, but limited by initial and cumulative errors [18] IV.…”