Double-String Battery System with Reconfigurable Cell Topology Operated as a Fast Charging Station for Electric Vehicles

Jan Engelhardt, Jan Martin Zepter, Tatiana Gabderakhmanova, Gunnar Rohde and Mattia Marinelli
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Jan Engelhardt: Department of Electrical Engineering, Risø Campus, Technical University of Denmark, 4000 Roskilde, Denmark
Jan Martin Zepter: Department of Electrical Engineering, Risø Campus, Technical University of Denmark, 4000 Roskilde, Denmark
Tatiana Gabderakhmanova: Department of Electrical Engineering, Risø Campus, Technical University of Denmark, 4000 Roskilde, Denmark
Gunnar Rohde: Nerve Smart Systems ApS, 4000 Roskilde, Denmark
Mattia Marinelli: Department of Electrical Engineering, Risø Campus, Technical University of Denmark, 4000 Roskilde, Denmark

Energies, 2021, vol. 14, issue 9, 1-19

Abstract: This paper introduces a novel design of an electric vehicle (EV) fast charging station, consisting of a battery energy storage system (BESS) with reconfigurable cell topology. The BESS comprises two battery strings that decouple the power flow between EV and grid, to enable charging powers above the grid capacity. The reconfigurable design is achieved by equipping the battery cells with semiconductor switches and serves two main purposes. First, it aims at solving cell unbalance issues to increase safety, reliability, and lifetime of the battery. Second, it enables the BESS to actively control the EV charging process by changing its cell configuration in a real-time fashion, making a DC-DC converter redundant. The paper presents a modelling approach that captures the reconfigurable design including the controlling algorithm used for cell engagement. The simulation results show that the BESS is able to fulfil the EV request with sufficient accuracy for most of the fast charging process. However, the switching of cells leads to variations in the charging current that can potentially exceed the tolerance band defined in IEC61851-23. Therefore, complementary measures are suggested to achieve a suitable current control during all phases of the charging process. The estimated BESS efficiency during the EV fast charging process is 93.3 %. The losses caused by the reconfigurable design amount to 1.2 % of the provided energy. It is demonstrated that the proposed design has a competitive efficiency compared to a battery buffered fast charging station with DC-DC converter.

Keywords: adaptive cell switching; battery balancing; battery management system; battery energy storage system; DC-DC converter; electric vehicle; energy efficiency; fast charging; reconfigurable battery (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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