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A Control Method for Battery Heating Using Alternating Current
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0002-6283-7661
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(English)Manuscript (preprint) (Other academic)
Keyword [en]
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: urn:nbn:se:kth:diva-228027OAI: oai:DiVA.org:kth-228027DiVA, id: diva2:1206321
Note

QC 20180518

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-05-18Bibliographically approved
In thesis
1. Interactions between battery and power electronics in an electric vehicle drivetrain
Open this publication in new window or tab >>Interactions between battery and power electronics in an electric vehicle drivetrain
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:nbn:se:kth:diva-228030 (URN)978-91-7729-837-3 (ISBN)
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

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Soares, RúdiBessman, AlexanderWallmark, OskarLindbergh, GöranSvens, Pontus

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