Thomas Nemeth

Ongoing electrification among all vehicle classes and growing demands for efficiency and driving power lead to a modularization of electric drivetrains. Multiple traction machines and battery packs of different types and power ratings can be used to meet the requirements for all vehicle types. This study introduces a simulation methodology, that can be used to evaluate and optimize modular drivetrains and their components. A flexible simulation platform and the models of all components of the electric drivetrain (battery, dc-dc converter, inverter, traction machine) are presented. Novelties including silicon carbide based dc-dc converters and hybrid battery storage systems, are also described in detail. The functionality of this simulation tool is demonstrated with a comparison of three drivetrain configurations for a sports car. Finally, the simulation results are used to demonstrate the advantages and disadvantages of each topology.

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.