An improved Ampere-hour method for battery state of charge estimation based on temperature, coulomb efficiency model and capacity loss model

Abstract

Coulomb efficiency and available capacity affect the precision of Ampere-hour method. Both coulomb efficiency and available capacity vary with temperature and discharge current rate. In this study, some experiments of a 27Ah Nickel Metal Hydride battery were undertaken to determinate the coulomb efficiency. These experiments were undertaken at −18°C, −12°C, 0 °C, 25°C with 1/3C, 1C, 3C charge rate and 1/3C discharge rate. Then, an improved coulomb efficiency model was proposed, which is based on temperature and charge rate. Moreover, an available capacity loss model was built based on experiments of 1/3C discharge rate at −18°C, −12°C, 0°C, 25°C. In addition, an improved Ampere-hour method based on temperature, coulomb efficiency and capacity loss model was built to estimate battery state of charge. The proposed method is verified by experiment and the result shows good precision.