Comparative Study of State of Charge Estimation Under Different Open Circuit Voltage Test Conditions for Lithium-Ion Batteries

The state of charge (SOC) is an essential indicator needed for a proper and safe operation of a battery. A large majority of methods used to estimate SOC rely on the open circuit voltage (OCV) curve. The OCV-SOC relationship is characteristic of the battery chemistry but it may also be affected by the temperature, aging or even the measurement procedure. In this work, the effect of these factors on the OCV curve is analyzed and their influence on the SOC estimation is studied. For this purpose an extended Kalman filter (EKF) has been used to compare the SOC estimation performance under different conditions. Also, the results obtained by two different methods have been compared, at two different aging states and various temperatures in the range 5-40°C.