An Improved Coulomb Counting Approach Based on Numerical Iteration for SOC Estimation With Real-Time Error Correction Ability

Abstract

The coulomb counting (CC) approach is widely used in SOC estimation due to its simplicity and low calculation cost. However, in practical applications, the lack of error correction ability limits its accuracy due to the measured noise in the practical occasion. To address the issue, an improved CC (ICC) approach based on numerical iteration is proposed in this paper. In the proposed approach, a battery model based on a 2nd-order, RC circuit is first formulated to determine the SOC-OCV curve, R-OCV curve, and inner parameters. In the model, the slow dynamic and fast dynamic voltages are described separately, and are utilized for battery state assessment. Then, the SOC will be estimated by the CC approach at the unsteady state but through a numerical iteration approach at steady state. Consequently, the accumulative SOC error from the CC approach will be corrected when the numerical iteration approach is applied. Furthermore, a compensation coefficient is employed into the CC approach to reduce the error accumulation rate. Hence, the proposed ICC approach could make full use of the advantages of conventional CC in low computational demand and numerical iteration approach in error correction. Finally, an experiment platform was built, where two kinds of current sensors with different measuring accuracy were employed to simulate the measured current with and without noise, respectively. The experimental results suggest that the accumulative SOC error can be corrected in real-time and the SOC error is reduced to 1%. The error accumulation rate of SOC is effectively reduced compared with traditional CC approach, simultaneously, more than 90% of the calculation time can be reduced compared with EKF.