SOC estimation of LiNi1/3Co1/3Mn1/3O2 battery using Unscented Kalman Filtering Method

LiNi_1/3Co_1/3Mn_1/3O₂, well known as the ternary material, is currently considered as one of the promising cathode materials for lithium-ion battery (LIB). In application, accurate estimation for state of charge (SOC) is crucial for the performance and safety use of LIB. However, it is a hard work as the SOC cannot be directly measured and is affected by many factors, such as ambient temperature, current rate and cycle number. Moreover, the influence of electromagnetic interference on measurement results (current, voltage and temperature etc.) makes the situation more terrible. In this paper, an approach of SOC estimation for LiNi_1/3Co_1/3Mn_1/3O₂ battery, which is based on the Unscented Kalman Filtering (UKF) is presented. An improved model for online SOC estimation under abominable operating conditions is presented, in which the battery rated capacity variation with ambient temperature and discharge current rate are taken into consideration. A modified two-order RC equivalent circuit model is employed to simulate the battery characteristics, based on which the state-space equation of battery is established. Experimental results show that the presented model can capture the battery characteristics very well and the UKF-based SOC estimator can ensure the estimation accuracy even if the measurement is incorrect.