Full vehicle simulation and exploration of a range extended electric vehicle battery pack and thermal management system in diurnal operating environments
A full vehicle model is created in Autonomie to represent a production extended range electric vehicle (EREV), specifically including the high voltage battery pack which is validated in dynamic operation against experimental data. Vehicle data is utilized as comparative input to a thermal equivalent circuit model developed analytically which aims to capture and understand the heat propagation from the cells through the entire pack, to and from the environment. The inclusion of production hardware and the liquid battery thermal management system components into the physical model considers detail geometric properties to calculate thermal resistances of components (conduction, convection and radiation) along with their associated thermal capacitances. Analog equivalent circuit simulations using PSPICE are compared to experimental results in order to validate internal temperature nodes and the heat rate through various elements with heat flux sensors; all used to refine the model. The solar data, diurnal temperature and terrain are included in the simulations to model the effects of gradient, convection and road radiation on the battery pack; both stationary and through drive cycles.
The thermal equivalent circuit accurately quantifies the heat flow dynamics of the battery. Convection and radiation sources primarily influenced the baseplate and underbody shield components whereas cell heat propagation was closely linked to cell retention frame hardware details. The distribution of cooling indicated close to 90% was directed to the cell while the remaining 10% went to the surrounding hardware. Modeling a quiescent background cooling showed the ability to reduce the diurnal temperature effects on the battery pack at the 50 watt level. The addition of insulation in key areas delineated the ability to reduce initial cell temperatures for all drive cycles, while a miniscule amount added between the cell and retention frame interface showed increased cooling capacity directed towards the cells nearing 100%. The models developed incorporated many elements which were neglected or highly simplified in all previous works and the methodology developed highlights an ability to generate accurate dynamic results with little computational power. This is a prerequisite to enable predictive controls and accurate onboard system diagnostics to extend the pack???s operational life
