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Aging effects of AC harmonics on lithium-ion cells
KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.ORCID-id: 0000-0002-6283-7661
Vise andre og tillknytning
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
Emneord [en]
lithium-ion, ripple-current, harmonics, aging
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-228029OAI: oai:DiVA.org:kth-228029DiVA, id: diva2:1206322
Merknad

QC 20180518

Tilgjengelig fra: 2018-05-16 Laget: 2018-05-16 Sist oppdatert: 2018-05-18bibliografisk kontrollert
Inngår i avhandling
1. Interactions between battery and power electronics in an electric vehicle drivetrain
Åpne denne publikasjonen i ny fane eller vindu >>Interactions between battery and power electronics in an electric vehicle drivetrain
2018 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2018. s. 74
Serie
TRITA-CBH-FOU ; 2018:27
HSV kategori
Forskningsprogram
Kemiteknik; Elektro- och systemteknik
Identifikatorer
urn:nbn:se:kth:diva-228030 (URN)978-91-7729-837-3 (ISBN)
Disputas
2018-06-15, E2, E-huset, huvudbyggnaden, våningsplan 3, Lindstedtsvägen 3, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Energy Agency
Merknad

QC 20180518

Tilgjengelig fra: 2018-05-18 Laget: 2018-05-17 Sist oppdatert: 2018-05-18bibliografisk kontrollert

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