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Integration of Magnified Alternating Current in Battery Fast Chargers based on DC-DC Converters using Transformerless Resonant Filter Design
KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. (EmadLab)ORCID iD: 0000-0002-9481-7366
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.ORCID iD: 0000-0002-6283-7661
Chinese University of Hong Kong.
(English)In: IEEE Transactions on Transportation ElectrificationArticle in journal (Refereed) Submitted
Abstract [en]

For safety and longevity reasons, in subzero temperatures, lithium-ion batteries can only be charged after precommissioningtheir temperature. Therefore, in such conditions fast charging depends on fast heating. Recently,the injection of AC currents into lithium-ion batteries has been reported as a technique with potential to decreaseheating time. This paper proposes a method based on a multi-objective algorithm for DC-DC converter designusing transformerless resonant filters. The method enables the DC-DC converters to produce magnified AC currentin addition to the DC current. Using the proposed design method, a topological survey of DC-DC converters withmagnified AC current capability composed of either half- or full-bridge switch arrangements is carried out. Inthe presented experimental setup, it is demonstrated that by using an LCL circuit with specific component valuesand a full-bridge switch arrangement, magnifications of up to 15.7 may be reached. Further, by matching theswitching frequency with the frequency where the LCL and the battery resonate, for the same injected AC current,the current flowing in the semiconductors and the switching frequency could be reduced. This allowed a lossreduction in the semiconductors of up to 75%, when compared with an equivalent DC-DC converter enabled toproduce a non-magnified AC current.

Keywords [en]
Batteries, DC-(DC/X·AC) converters, fast charging, fast heating, injection of alternating current.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-251663OAI: oai:DiVA.org:kth-251663DiVA, id: diva2:1316363
Funder
Swedish Energy Agency, 37434-1
Note

QC 20190520

Available from: 2019-05-17 Created: 2019-05-17 Last updated: 2019-06-14Bibliographically approved
In thesis
1. Modeling and Analysis of the Interaction of Batteries and Power Electronic Converters
Open this publication in new window or tab >>Modeling and Analysis of the Interaction of Batteries and Power Electronic Converters
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the interaction of batteries and power electronic converters in automotive applications. Even if the additional heating caused by (unwanted) alternating currents is disregarded, there has been a concern that alternating currents can be harmful for batteries. For that reason, alternating currents can be filtered using capacitors and/or by sophisticated hardware. In this work, the concern whether alternating currents are harmful to batteries is studied particular focus on large, lithium-ion cells for use in automotive applications.First, the harmonic content in the battery current of two, commercial hybrid-electric busses were measured and analysed. The most prominent harmonic had a peak magnitude higher than 10% of the maximum direct current level (160 A) arising at frequencies below 150 Hz. The maximum amplitude detected of a harmonic caused by the voltage source converter’s switching action was around 10 A and occurred at a frequency of 2 kHz. An experimental setup with alternating current capability for evaluating large lithium-ion cells has been designed and built. Twelve lithium-ion cells were cycled at a rate if 1 C during approximately 2000 cycles (corresponding to approximately one year). The cells were cycled with an superimposed alternating current of 1 Hz, 100 Hz, or 1 kHz while the rest of the cells were cycled with direct current (only), injected with alternating current (only), or no current at all (calendar aging). No negative effects caused by the alternating current was identified in terms of capacity fade and power fade for the tested lithium-ion cells. A comparison between sinusoidal current-ripple charging and conventional constant-current constant-voltage charging was also carried out. Three lithium-ion cells were cycled (ten times) with different ac currents superimposed during charge. The results were analyzed statistically and no significant improvements in terms of charging time or charging efficiency were observed in any of the charging tests using an superimposed ac current. The injection of alternating currents into batteries for heating purposes has also been studied and a control method for battery heating using an ac current was proposed. The proposed controller is applicable regardless of the LIB’s subsequent impedance nature (capacitive, inductive or resistive). Further, a design process for the generation of magnified alternating currents in dc-dc converters was presented. By matching the switching frequency with the frequency where the LCL filter and the battery resonate, the current flowing in the semiconductors and the switching frequency could be reduced. In a small experimental setup using a single lithium-ion cell, using an LCL-resonant circuit and a full bridges witch arrangement, magnifications of up to 15.7 were reached. This allowed for a loss reduction in the semiconductors of up to 75%, when compared to an equivalent dc-dc converter enabled to produce anon-magnified ac current. 

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2019. p. 184
Series
TRITA-EECS-AVL ; 2019:45
Keywords
Alternating current, aging, electric vehicles, harmonics, lithium-ion batteries, power converter, resonant filters, ripple, temperature control.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-251665 (URN)978-91-7873-187-9 (ISBN)
Public defence
2019-06-05, Kollegiesalen, Brinellvägen 8, Kungliga Tekniska högskolan, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20190517

Available from: 2019-05-17 Created: 2019-05-17 Last updated: 2019-06-17Bibliographically approved

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