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University of Stuttgart

Battery electric vehicles, or BEVs, not only allow for emission free traveling but are also capable of offsetting carbon dioxide emissions in the environment. While the most environmentally conscientious drivers are happy to do their duty to protect and preserve the climate, this cannot come at the detriment of speed, endurance, and comfort.

By analyzing different drive cycles for various environmental conditions and considering the comfort of the passenger, one thing above all else, becomes the key driver in battery electric vehicle design, the driving range of the car must be substantial if it is to be competitive in today’s marketplace.”

Markus Auer, University of Stuttgart

Summary

Markus Auer of the University of Stuttgart explores the influence of battery temperature and air conditioning (passenger comfort) on the battery and the range for the vehicle. Several key factors are considered as boundary conditions. A Flowmaster model was set up and linked with Matlab/Simulink to simulate the vehicle, including a complex battery thermal model.

The Problem

By design, battery electric vehicles are more energy efficient than combustion driven vehicles resulting in much less wasted heat to warm the passenger cabin. Therefore, the cabin has to be heated with energy delivered from another source or from the battery. However when the energy is taken from the battery, the effective range of the vehicle is drastically reduced. Hence, thermal as well as energy management is very important.

The Solution

The crucial factor for the successful introduction to market of electric powered vehicles is a substantial driving range. Nevertheless, the comfort of the car is an important factor that no car owner is willing to forgo. If the energy for heating, ventilation and air conditioning (HVAC) is drawn from the traction battery, the driving range is affected severely, putting comfort in competition with the driving range for energy. To accurately predict how the driving range is influenced by the need for comfort, a predictive simulation tool is required. To begin the vehicle is modeled via a coupled simulation between Matlab/Simulink and Flowmaster. The desired driving cycle is defined by a velocity over time profile. Based on vehicle parameters, such as drag coefficient and frontal area, the necessary torque and rotational speed of the electric motor are calculated and are used to calculate the heat flux of the varying components. The derived heat fluxes as well as different rotational speeds of the electric AC compressor and electric coolant pumps are fed into the thermo hydraulic solver in Flowmaster. Based on the values and the thermo hydraulic model, Flowmaster calculates the temperatures and required electric power which are then sent back to Matlab.

The Results

By analyzing different drive cycles for various environmental conditions and considering the comfort of the passenger, one thing above all else, becomes the key driver in battery electric vehicle design, the driving range of the car must be substantial if it is to be competitive in today’s marketplace. All these parameters influence battery performance which is why efficient battery cooling and heating, is extremely important for the range and battery lifetime. This is especially significant as the efficient working temperature range is narrow. Not to mention additional power consumers such as infotainment systems and charging of any consumer electronics, such as cell phones, which were not considered in this study but are ever-increasing in today’s automotive environment.This study is an excellent demonstration of the use of system simulation coupled with a complex battery model and an energy manager in Matlab/Simulink to improve the driving range of a battery electric vehicle.

About the University of Stuttgart

Markus Auer studied Automotive Engineering at the University of Stuttgart, Germany. He is working as a research assistant since October 2010 at the Institute of Internal Combustion Engines and Automotive Engineering (Institut für Verbrennungsmotoren und Kraftfahrtwesen) of the University of Stuttgart with a focus on battery electric vehicles

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