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World Electric Vehicle Journal is published by MDPI from Volume 9 issue 1 (2018). Articles in this Issue were published by The World Electric Vehicle Association (WEVA) and its member the European Association for e-Mobility (AVERE), the Electric Drive Transportation Association (EDTA), and the Electric Vehicle Association of Asia Pacific (EVAAP). They are hosted by MDPI on mdpi.com as a courtesy and upon agreement with AVERE.
Open AccessArticle

Energy Optimal Operation of Hybrid Battery Systems and Comparison to a Single-Cell Reference System for Electric Vehicles Including the Aged State of High Energy Cells

1
Corporate Sector Research and Advance Engineering, Robert Bosch GmbH, 71272 Renningen, Germany
2
Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University, 52066 Aachen, Germany
3
Aachen Research Alliance, JARA-Energy, Germany
*
Author to whom correspondence should be addressed.
World Electr. Veh. J. 2016, 8(2), 315-326; https://doi.org/10.3390/wevj8020315
Published: 24 June 2016
PDF [816 KB, uploaded 15 May 2018]

Abstract

In battery electric vehicles the battery system has to satisfy demanding requirements. On the one hand, high power capabilility has to be provided for varying states of charge and temperature. On the other hand, the battery system should achieve a maximum service life, optimal energy efficiency and a high overall driving range. This paper compares a conventional single-cell battery system with two hybrid battery system topologies that aim at improving the mentioned aspects of the conventional system. The hybrid battery systems each comprise two battery parts connected via a dc-to-dc converter, one part including lithium-ion battery cells optimized for high energy density and the other part equipped with high power density type lithium-ion cells. An optimal control problem is formulated and solved with Dynamic Programming. The mentioned topologies are then compared in terms of energy efficiency, power capability and current distribution. A real life driving cycle power demand is used for this comparison. It can be shown that the hybrid battery system reduces the occurrence of high current rates on the high energy battery part and shows better energy efficiency when operated with aged high energy battery cells. Furthermore the hybrid battery system’s potential to obtain a high power capability in low state of charge regions is shown.
Keywords: BEV (battery electric vehicle); lithium battery; power management; energy consumption; cycle life BEV (battery electric vehicle); lithium battery; power management; energy consumption; cycle life
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Wegmann, R.; D¨oge, V.; Sauer, D.U. Energy Optimal Operation of Hybrid Battery Systems and Comparison to a Single-Cell Reference System for Electric Vehicles Including the Aged State of High Energy Cells. World Electr. Veh. J. 2016, 8, 315-326.

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