Modeling and Evaluation of Li-Ion Battery Performance Based on the Electric Vehicle Field Tests 2014-01-1848
In this paper, initial results of Li-ion battery performance characterization through field tests are presented. A fully electrified Ford Escape that is equipped by three Li-ion battery packs (LiFeMnPO4) including an overall 20 modules in series is employed. The vehicle is in daily operation and data of driving including the powertrain and drive cycles as well as the charging data are being transferred through CAN bus to a data logger installed in the vehicle. A model of the vehicle is developed in the Powertrain System Analysis Toolkit (PSAT) software based on the available technical specification of the vehicle components. In this model, a simple resistive element in series with a voltage source represents the battery. Battery open circuit voltage (OCV) and internal resistance in charge and discharge mode are estimated as a function of the state of charge (SOC) from the collected test data. It is shown that although the OCV should be measured under no-load condition, still it can be estimated with an acceptable accuracy (∼5%) from the driving data. Afterwards, performance of the battery model is evaluated in terms of prediction of state of charge (SOC), charged and discharged energy over several driving conditions as well as tracking the battery temperature profile. The model shows a high accuracy (within 5% error) in both cumulative energy and temperature prediction. Future work includes study of battery degradation incorporating real-life drive cycles.