Science Inventory

Modeling and Validation of 48V Mild Hybrid Lithium-ion Battery Pack

Citation:

Lee, S., J. Cherry, M. Safoutin, J. McDonald, AND M. Olechiw. Modeling and Validation of 48V Mild Hybrid Lithium-ion Battery Pack. SAE Technical Paper Series. SAE International, Warrendale, PA, , 11, (2018). https://doi.org/10.4271/2018-01-0433

Impact/Purpose:

The purpose of this work was to develop and validate a 48V lithium-ion battery model that can be integrated into EPA's ALPHA vehicle simulation model and that can also be used in other commercially-available vehicle simulation models. The battery pack model enables fuel economy and greenhouse gas (GHG) emissions to be estimated by simulating the effects of battery cell power capacity, the battery state-of-charge operating window, discharge and charge power limits, battery pack temperatures, battery cell internal resistance, and battery management system thermal control strategies. This work was conducted as part of the U.S. EPA's Light-duty Vehicle GHG Midterm Evaluation.

Description:

As part of the Midterm Evaluation of the 2017-2025 Light-duty Vehicle Greenhouse Gas (GHG) Standards, the U.S. Environmental Protection Agency (EPA) developed simulation models for studying the effectiveness of 48V mild hybrid technology for reducing CO2 emissions from light-duty vehicles. Simulation and modeling of this technology requires a suitable model of the battery. This paper presents the development and validation of a 48V lithium-ion battery model that will be integrated into EPA's ALPHA vehicle simulation model and that can also be used within Gamma Technologies GT-DRIVE vehicle simulations. The battery model is a standard equivalent circuit model with two resistance-capacitance (RC) blocks. Resistances and capacitances were calculated using test data from an 8Ah, 0.4kWh, 48V (nominal) lithium iron phosphate (LiFePO4) battery supplied by A123 and specifically developed for 48V mild hybrid vehicle applications. The A123 battery has 14 pouch-type lithium ion cells arranged in a 14 series and 1 parallel (14S1P) configuration. The RC battery model was validated using battery test data generated by a hardware-in-the-loop (HIL) system that simulated the impact of mild hybrid electric vehicle (MHEV) operation on the A123 48V battery pack over U.S. regulatory drive cycles. The HIL system matched charge and discharge data originally generated by Argonne National Laboratory (ANL) during chassis dynamometer testing of a 2013 Chevy Malibu Eco 115V mild hybrid electric vehicle. All validation testing was performed at the Battery Test Facility (BTF) at the U.S. EPA National Vehicle and Fuel Emissions Laboratory (NVFEL) in Ann Arbor, Michigan. The simulated battery voltages, currents, and state of charge (SOC) of the HIL tests were in good agreement with vehicle test data over a number of different drive cycles and excellent agreement was achieved between RC model simulations of the 48V battery and HIL battery test data.