Thermal Management of a Battery Electric Vehicle: How thermal management strategies can improve the performance of a battery electric vehicle for various driving cycles and conditions

Abstract

The automotive industry is developing due to changes in climate, legislations and customer de- mands. Battery electric vehicles (BEVs) are becoming more important with their zero tailpipe emissions and their share is expected to rise in the future. A major problem concerning BEVs is the driving range which is affected by demanding ambient conditions and puts the thermal management system (TMS) in focus. The TMS has an important role to ensure that the battery, electric motor and cabin compartment are kept in certain temperature intervals where comfort, efficiency and safety are optimal. In this thesis a complete system-level model for a BEV and its TMS is developed in Amesim simulation software. In Amesim vehicle-level simulations are performed to investigate different thermal management strategies to analyze vehicle energy efficiency. First the model validation is performed for different BEV models using their official data for driving range. The trends were well captured for WLTP, EPA, NYCC, Artemis highway and Artemis urban driving cycles at the ambient temperatures -15°C, 0°C, 20°C and 40°C. The model is the employed to analyze the effects of different TM strategies including precondition- ing, heating the battery for regenerative braking, limiting the current-peaks and a holistic approach where the battery and electric motor share a common thermal management circuit. Simulation results show that preconditioning BEVs by heating up or cooling down the components provides a major difference compared to not precondition where range can drop significantly depending on driving cycle and ambient conditions. Using the energy from the battery to heat it up shows great potential, however, the outcome depends on initial and target temperatures, battery energy levels, battery size and the driving cycle. Provided this information the vehicle could estimate when to heat up the battery, which can result in between 10-250 % being recuperated of the invested energy for heating by regenerative braking. Limiting the current-peaks and using the holistic approach results in up to 2.5% energy savings increasing driving range in certain driving cycles and tem- peratures. A combination of limiting the current peaks and using the same thermal management circuit for the motor and battery results in increased range in all driving cycles and 4 temperature levels expect EPA. The increased energy savings and range were below 1% in most scenarios but reached 2.1% in the best case. By implementing these strategies the efficiency in BEVs can be increased increased by several percent, which if implemented at large scale can impact the total emissions and contribute to a better experience for customers especially in demanding conditions.