Abstract
Commercial electric vehicles nowadays are powered by a battery system containing one kind of lithium-ion battery cell. Due to the fixed ratio of the cells’ maximum power to nominal energy, the possibilities for designing power and energy of the battery pack independently are limited. The battery system’s energy and maximum power can only be scaled by adapting the number of cells and modules, and the parameters furthermore depend on the characteristics of the cells used. Additional power electronics in the form of one or more dc/dc converters can be used to form a hybrid battery system comprised of more than one pack and different cell technologies. This allows for individually designing each battery pack and thus optimizing the overall battery system specification. This work presents a battery dimensioning and optimization approach for single pack and hybrid battery systems. It is based on an evolutionary optimization algorithm and a detailed, modular Matlab-Simulink vehicle model. Studies on the advantages of hybrid batteries for different vehicle classes were carried out. Results indicate that optimized hybrid battery systems can lead to weight and volume savings and further advantages in total cost of ownership, for example, by enhanced battery life time or reduced investment costs. On the other hand, they require more complex control logic, which is also discussed in this paper.
Highlights
Electric vehicles (EVs) still suffer from slow market penetration in Germany and worldwide, German politics have sought for a quick ramp-up since 2011 [1] and are currently supporting purchases of new EVs with a monetary reward
To evaluate the concept of hybrid battery systems and compare the approach to the state of the art single battery pack approach, the developed tool chain was used for five different EVs: 3. Dimensioning Results
This work describes a methodology for the optimization of hybrid battery systems for automotive applications
Summary
Electric vehicles (EVs) still suffer from slow market penetration in Germany and worldwide, German politics have sought for a quick ramp-up since 2011 [1] and are currently supporting purchases of new EVs with a monetary reward. The main hurdles still in place are the lower mobility flexibility when using EVs due to their limited range compared to combustion driven vehicles, as well as their higher investment costs—at least, if not significantly funded. One of the main cost drivers of EVs is the battery system, cell prices have decreased over the last years [2]. A sophisticated dimensioning and design of the battery system is essential for the successful electrification of vehicles. Battery systems may be dimensioned conservatively in terms of initial energy to guarantee a certain range at the end of life. This may lead to systems outside the economical and ecological optimum
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