Modeling and Validation of Lithium-Ion Polymer SLI Battery 2019-01-0594

Lead-acid batteries have dominated the automotive conventional electric system, particularly in the functions of starting (S), lighting (L) and ignition (I) for decades. However, the low energy-to-weight ratio and the low energy-to-volume ratio makes the lead-acid SLI battery relatively heavy, large, and shallow Depth of Discharge (DOD). This could be improved by replacing the lead-acid battery by the lithium-ion polymer battery. The lithium-ion polymer battery can provide the same power with lightweight, compact volume, and deep DOD for engine idle elimination using start-stop function that is a basic feature in electric-drive vehicles. This paper presents the modeling and validation of a lithium-ion battery for SLI application. A lithium-metal-oxide based cell with 3.6 nominal voltage and 20Ah capacity is used in the study. A simulation model of lithium-ion polymer battery pack (14.4V, 80Ah) with battery management system is built in the MATLAB/Simulink environment. The experimental tests are performed in battery module-level, a four series-connected cells (14.4V, 20Ah), under various charging and discharging currents in a temperature chamber. The experimental data is used to calibrate the model parameters for validation. The simulation results show a 9% or less discrepancy in all continuous and pulse charge/discharge conditions. The developed simulation model could provide design guidelines for lithium-ion polymer battery applications in 12 voltage SLI, start-stop system, and 48 voltage mild hybrid electric vehicle.