PREDICTION OF LI-ION BATTERY DISCHARGE CHARACTERISTICS AT DIFFERENT TEMPERATURES AND DISCHARGE RATES BASED ON A HYBRID SOC ESTIMATION APPROACH

Vinitha Ramdas, M. Pramod, P. Satyanarayana, K. Venkatesh, M. Ravindra

Abstract: State of charge (SOC) is an important battery parameter which provides a good indication of the useful capacity that can be derived out of a battery system at any given point of time. Li-ion has become state of the art technology for commercial and aerospace applications due to the various advantages that they offer. For spacecrafts requiring long lifetime, SOC estimation is crucial for on-orbit as well as offline data analysis. On-orbit estimation of SOC should be carefully addressed, as this provides information on survivability of battery and also serves as input to Battery Management System (BMS). In addition, detailed offline data analysis of battery electrical characteristics, which indicate the SOC-Voltage relationship is important to assess the performance of the battery under various mission scenarios at both Beginning of life (BOL) and End of Life (EOL) of a spacecraft system. In this work, a hybrid SOC estimation method, incorporating coulomb counting and Unscented Kalman Filter (UKF) is used, to predict the BOL discharge behaviour of an 18650 commercial Li-ion cell at different temperatures and discharge rates. The experimental results are encouraging and the approach gives a prediction error of less than 10%. The study will serve as basis for life assessment of Li-ion cells and batteries used for GEO and LEO missions.

Keywords: Li-ion, State of Charge, Unscented Kalman Filter etc

DOI: https://doi.org/10.15623/ijret.2015.0411058