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Interactions between battery and power electronics in an electric vehicle drivetrain
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.ORCID iD: 0000-0002-0108-1872
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The electric machine and power electronics in electric and hybrid electric vehicles inevitably cause AC harmonics on the vehicle's DC-link. These harmonics can be partially filtered out by large capacitors, which today are overdimensioned in order to protect the vehicle's battery pack. This is done as a precaution, since it is not known whether ripple-current has any harmful effect on Li-ion  cells.

We have measured and analyzed the ripple-current present in a hybrid electric bus, and found that a majority of the power was carried by frequencies in the range 100~Hz to 1~kHz. The single most energetic harmonic in this particular vehicle is believed to have been caused  by a misaligned resolver in the motor.

We have also designed and built an advanced experimental set-up in order to study the effect of ripple-current on Li-ion cells in the lab. The set-up can cycle up to 16 cells simultaneously, with currents of up to 50~A including a superimposed AC signal with a frequency of up to 2~kHz. The cells' temperatures are controlled by means of a climate chamber. The set-up also includes a sophisticated safety system which automatically acts to prevent dangerous situations before they arise.

Using this set-up we tested whether superimposing AC with a specific frequency improves the charging performance of Li-ion cells. Statistical analysis found no improvement over regular DC cycling, and a physics-based model explains the experimental findings.

We have also investigated whether ripple-current accelerates the aging of Li-ion cells. Twelve cells were either calendar or cycle  aged for one year, with some cells being exposed to superimposed AC with a frequency of 1~Hz, 100~Hz, or 1~kHz. No effect was observed on any of capacity fade, power fade, or aging mechanism.

Finally we also tested whether it is possible to heat Li-ion cells from low temperatures using only AC. We propose a method for AC heating of Li-ion cells, and open the discussion for generalizing the technique to larger battery packs.

In conclusion, ripple-current has negligible effect on Li-ion cells, except for heating them slightly.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. , p. 74
Series
TRITA-CBH-FOU ; 2018:27
National Category
Other Chemical Engineering
Research subject
Chemical Engineering; Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-228030ISBN: 978-91-7729-837-3 (print)OAI: oai:DiVA.org:kth-228030DiVA, id: diva2:1206679
Public defence
2018-06-15, E2, E-huset, huvudbyggnaden, våningsplan 3, Lindstedtsvägen 3, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-17 Last updated: 2018-05-18Bibliographically approved
List of papers
1. Measurements and analysis of battery harmonic currents in a commercial hybrid vehicle
Open this publication in new window or tab >>Measurements and analysis of battery harmonic currents in a commercial hybrid vehicle
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2017 (English)In: 2017 IEEE Transportation and Electrification Conference and Expo, ITEC 2017, Institute of Electrical and Electronics Engineers Inc. , 2017, p. 45-50Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, the harmonic content of the battery current in a commercial hybrid vehicle (bus) is measured and analyzed for a number of different driving situations. It is found that the most prominent harmonic reaches peak magnitudes that can be higher than 10% of the maximum dc-current level with a maximum frequency less than 150 Hz. Further, it is found that this harmonic can be approximated using a fitted, simple analytical expression with reasonable agreement for all driving situations considered.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers Inc., 2017
Keywords
DC-link, Harmonic currents, Hybrid vehicles, Lithium-ion batteries, Permanent-magnet synchronous machine, Ripple, Voltage source inverter, Commercial vehicles, Electric batteries, Electric inverters, Electric utilities, Harmonic analysis, Lithium compounds, Permanent magnets, Secondary batteries, Vehicles, DC links, Permanent magnet synchronous machines
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-216277 (URN)10.1109/ITEC.2017.7993245 (DOI)000427121300009 ()2-s2.0-85028594346 (Scopus ID)9781509039043 (ISBN)
Conference
2017 IEEE Transportation and Electrification Conference and Expo, ITEC 2017, 22 June 2017 through 24 June 2017
Note

QC 20171213

Available from: 2017-12-13 Created: 2017-12-13 Last updated: 2018-05-17Bibliographically approved
2. An Experimental Setup with Alternating Current Capability for Evaluating Large Lithium-ion Batteries Cells
Open this publication in new window or tab >>An Experimental Setup with Alternating Current Capability for Evaluating Large Lithium-ion Batteries Cells
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(English)Manuscript (preprint) (Other academic)
Keywords
Alternating current, aging, battery testing, electric vehicles, GITT, HPPC, life cycle, lithium-ion batteries, ripple, SOC
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-228024 (URN)
Note

QC 20180518

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-05-18Bibliographically approved
3. Challenging Sinusoidal Ripple-Current Charging of Lithium-Ion Batteries
Open this publication in new window or tab >>Challenging Sinusoidal Ripple-Current Charging of Lithium-Ion Batteries
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2018 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 6, p. 4750-4757Article in journal (Refereed) Published
Abstract [en]

Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.

Place, publisher, year, edition, pages
IEEE Press, 2018
Keywords
Fast charging, lithium-ion (Li-ion) battery, sinusoidal ripple charging
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-223315 (URN)10.1109/TIE.2017.2772160 (DOI)000425618900031 ()2-s2.0-85034238750 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20180222

Available from: 2018-02-16 Created: 2018-02-16 Last updated: 2018-05-17Bibliographically approved
4. Aging effects of AC harmonics on lithium-ion cells
Open this publication in new window or tab >>Aging effects of AC harmonics on lithium-ion cells
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(English)Manuscript (preprint) (Other academic)
Keywords
lithium-ion, ripple-current, harmonics, aging
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-228029 (URN)
Note

QC 20180518

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-05-18Bibliographically approved
5. A Control Method for Battery Heating Using Alternating Current
Open this publication in new window or tab >>A Control Method for Battery Heating Using Alternating Current
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(English)Manuscript (preprint) (Other academic)
Keywords
Current control, electric model, injection of alternate current, internal heat, lithium-ion batteries, packaging, ripple, temperature control, thermal model
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-228027 (URN)
Note

QC 20180518

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-05-18Bibliographically approved

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Bessman, Alexander

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