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Estimering av kapacitet och kondition för litiumjon batterier
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
2009 (Swedish)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Estimation of State-Of-Charge and State-Of- Health for lithium-ion batteries (English)
Abstract [sv]

For att noggrannare kunna bestamma SOC (State-Of-Charge) och SOH (State-Of-Health) i Atlas

Copcos batteridrivna mutterdragare har en litteraturstudie over de vanligaste metoderna gjorts.

Utifran litteraturstudien valdes en metod for att mata SOC och tre metoder for att mata SOH. For

att metoderna ska kunna appliceras i verkligheten kravs att vissa kriterier uppfylls. Da batteriet

laddas ur med hoga strompulser far matningarna inte oka serieresistansen fran batteriet.

Dessutom har verktyget en processor i sig och darfor far inte strommen brytas for matningen.

Matningarna far inte heller pa annat satt paverka atdragningen eller stora anvandaren.

Grunden i arbetet ligger i att oka forstaelsen om litium-jon batterier genom att studera batteriers

uppbyggnad och bakomliggande kemi och fysik sa som termodynamiska- och kinetiska

samband. Som en fortsattning undersoks vilka fenomen som orsakar kapacitets- och

energiforluster i cellen. Utifran den kunskapen gors en ekvivalent elektrisk modell som forklarar

cellens beteende nar den laddas ur.

I metoden for att mata SOC har det undersokts hur val vilospanningen mellan atdragningarna

stammer overens med SOC. Med hjalp av algoritmer som kompenserar for hur cellen har laddats

ur kan kvarvarande dragningar i procent beraknas med god noggrannhet. Dessutom har viktig

information om nar en cell bor anses vara urladdad setts i matningarna.

I den forsta metoden for att mata SOH undersoktes hur forandringen av impedansspektrumet

beror pa cellens aktuella kapacitet. Det har aven visats att det racker med matningar vid enstaka

frekvenser i impedansspektrumet for att bestamma SOH.

I den andra metoden gjordes forsok dar batteriet belastades med tva strompulser och

spanningsfallet vid den andra pulsen mattes. Utifran resultaten fran forsoken kan den aktuella

kapaciteten raknas fram. Dessutom har det visats att spanningsfallet och intressanta delar av

impedansspektrumet har ett linjart samband.

Som en tredje metod undersoktes det hur val tiden som batteriet laddas med konstant spanning

stammer overens med den aktuella kapaciteten. Samtliga metoder som har testats for att mata

SOH fungerar. De har dock olika for- och nackdelar om de skulle implementeras i

verktygssystemet.

Abstract [en]

In order to determine the SOC (State-Of-Charge) and the SOH (State-Of-Health) more

accurately in battery powered nutrunners made by Atlas Copco, a literature study of the most

common methods has been conducted. From the literature study one method for the

measurement of the SOC and three methods for the measurement of the SOH were chosen. In

order to apply these methods in reality, certain criteria must be fulfilled. Since the battery is

discharged with high current pulses the series resistance from the battery is not allowed to

increase during the measurements. Furthermore the nutrunner has an integrated DSP and

therefore the power can not be cut to do measurements. Also, the measurements can not in any

way affect the tightening of the nut or interrupt the usage of the nutrunner.

The fundamental part of the thesis is increasing the understanding of lithium-ion batteries by

studying their inner structure and basic chemistry and physics like thermodynamic- and kinetic

relations. The phenomena which cause energy- and capacity losses are also evaluated. From that

knowledge an equivalent electric model explaining the behavior of the battery when charged or

discharged, is made.

In the method for the SOC measurements an evaluation of how well the relax potential between

the tightenings correlate with the SOC. By using an algorithm which compensates for how the

cell is discharged the remaining tightenings in percentage can be calculated whit high accuracy.

Furthermore important information of when a cell should bee considered empty has been found.

The first method for measurements of the SOH determines how the changes in the impedance

spectrum correlate with the actual capacity. It has also been shown that only measurements of

single frequencies are needed in order to determine the SOH.

In the second method experiments were made where the battery was discharged with two current

pulses and the voltage drop in the second pulse was measured. From the voltage drop

measurements the actual capacity can be calculated. Furthermore it has been shown that the

relation between the voltage drop and interesting parts of the impedance spectrum is linear.

As a third method the correlation between the time that the battery is charged with constant

voltage and the actual capacity was evaluated. All three methods for measurements of the SOH

have been concluded working. They would, however, all have different pros and cons if

implemented in the tool system.

Place, publisher, year, edition, pages
2009.
Series
MMK 2009:27 MDA 338
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-99670OAI: oai:DiVA.org:kth-99670DiVA: diva2:542451
External cooperation
Atlas Copco Tools,Peter Kjellqvist
Uppsok
Technology
Supervisors
Examiners
Available from: 2012-08-01 Created: 2012-08-01 Last updated: 2012-08-01Bibliographically approved

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