Initial state of charge estimation of battery using impedance measurement for electrical vehicle applications

Abstract

An accurate determination of the battery State-of-Charge (SOC) represents an increasingly important technology-based challenge in the Battery Electric Vehicles (BEVs) not only for both extending the battery life span and displaying to the user its usable energy before further recharging process but also for managing the battery to its optimal potential. Either frequent BEV re-charge or over-discharge shortens the battery’s lifetime. This study deals with the development of a hybrid Coulomb counting/impedance measurement approach to properly determine on-board the BEV’s SOC, eliminating the inaccuracies associated with the counting method. Initially, the battery impedance measurement methodology is dedicated for the on-board estimation of the initial SOC in real operating conditions. Then using the Coulomb counting method, the SOC is estimated using the pre-determined initial value. The originality of this work consists of proposing a real time, on-board and cost-effective method to estimate the initial battery SOC coupled with the Coulomb Counting method which is an accurate method under the condition of prior knowledge of the initial SOC which is available with the proposed technique. The corresponding mathematical formula that provides acceptable SOC estimation is deduced. A simple electrical circuit is designed to validate this approach in realistic operating conditions. Experimentally, the BEV characterization is successfully checked and impedance measurement are verified for two different battery technologies mainly Li-Ion and Lead-Acid Battery using a battery test bench built via CompactRIO™ and LabVIEW™ software. The experimental and theoretical verification is given to validate the effectiveness the proposed method.