State of charge estimation of lithium-ion battery using Kalman filters

In this paper we propose an accurate state of charge (SOC) estimation method for a lithium-ion battery for hybrid electric vehicle (HEV) and electric vehicles (EV) use. Although it is important to accurately determine the SOC of a battery to achieve maximum efficiency and safety, none of the existing methods has achieved this perfectly. To address this issue, a model-based approach using a cascaded combination of two Kalman filters, “Series Kalman Filters,” is proposed and implemented. Its validity is verified by performing a series of simulations under a basic HEV operating environment.