Electric vehicle cold start range estimation through battery-in-loop simulations within a virtual driving environment

© 2020 SAE International. All Rights Reserved. Lithium-ion (Li-ion) batteries have become a research focus in the field of electric and hybrid electric vehicles, due to key advantages such as high specific energy, high energy density and low self-discharge rate in comparison with other battery technologies. Nevertheless, key issues involving safety, performance, cost, charging time and durability restrict mass market adoption of electric vehicles. Cold-temperature operation of Li-ion batteries is currently a subject of major research efforts. The effects of low temperature reduce the available energy of the battery and increase its internal impedance. Moreover, Li-ion batteries experience serious degradation mechanisms at low temperatures, strongly affecting performance, which poses difficulties for cold-climate countries. In this work, a battery-in-the-loop experiment has been set up to estimate and analyze Li-ion battery cold start ranges at temperatures down to-40 °C. This experimental setup is connected to the open integration and test platform CarMaker from IPG Automotive to evaluate cold start range both through standardized automotive duty cycles and within a virtual test environment designed to replicate real-world test driving. In addition, a non-isothermal equivalent circuit battery model has been developed in CarMaker for Simulink and validated against experimental data. Effects of cold temperatures on the capacity and power fade of Li-ion battery technology are studied, as well as important thermal aspects, including effects of changing battery heat transfer coefficient to replicate different thermal management strategies. Range discrepancies between standardized duty cycles and a representative driving environment are also explored. Overall, this work contributes to identify key improvements in Li-ion battery thermal management for performance and durability enhancement during cold start.