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Energies 2017,10, 1503
Withameasuredbatterycurrent (It), thedifferenceof theDODinanoperatingperiod(T) canbe
computedby:
ΔDOD= ∫ t0+T
t0 Itdt
Crated ×100%. (4)
ByconsideringtheSOH, theSOCisestimatedas:
SOC(t)=SOH(t)−DOD(t). (5)
In order to improve the convergenceperformanceof SOCestimation, an accuratemethod to
determine the initial status of the batteries will be used. However, unlike the lab environment,
it is hard to know the exact initial SOC andDODof the battery. Therefore, a self-initialization
methodfor thebatterysystemisproposedandimplementedtoprovidepriorconfigurationduringthe
initializationstage.
At thechargingstage, thevariationsof thebatteryvoltageandbatterycurrentwhenthebattery
is charged by the constant current–constant voltage (CC–CV)mode are usually specified by the
manufacturer.With theconstantchargingcurrent, thebatteryvoltage increasesgraduallyandreaches
the threshold.Once thebatteryhasbeenchargedbytheconstantvoltagemode, thechargingcurrent
reducesrapidlybeforeitmoregraduallydecreases. Eventually, thecurrentwill reachalmostzerowhen
it is fullycharged.Thischargingcurvecanbeconverted into therelationshipbetweenthecharging
voltageandtheSOC,duringtheconstantcurrentstage. Byusingtherelationshipbetweenthecharging
currentandtheSOCduringtheconstant-voltagestage, the initialSOCvaluecanbeobtained.
At thedischargingstage, the typicalvoltagecurvesatdifferentdischargingcurrentsaregiven
bythemanufacturer.Ahighercurrentwill causea fasterdecline in the terminalvoltage,andleadto
ashorteroperationtime. TherelationshipbetweentheSOCandthedischargingvoltageatdifferent
currents canbeobtained. At theopen-circuit stage, the relationshipbetweenopen-circuit voltage
(OCV)andSOCisneeded. Thebattery isdischargedbydifferentcurrentsbeforedisconnectingfrom
the load. TheOCVcanbeusedtoestimateSOCifa longperiodof relaxation isgivenfor the transient
tosettle to its steadystate. Figure3 is theflowchart to indicate theself-initializationprocedures for
SOCestimationwhenthesystemrestartsaftera longperiodof relaxation.
Figure3.FlowchartofSOCself-initializationandupdating(DOD:depthofdischarge,SOH:state-of-charge,
OCV:opencircuitvoltage,EEPROM:electricallyerasableprogrammableread-onlymemory).
2.3. SmartFault-DiagnosisStrategies
As the LIBs provide a high-energy-density power, the system must be able to detect the
abnormality inreal-timetoensure thesafetyof theusersandefficientpowersupplyunderunexpected
conditions, suchasanexternal short circuit. ThesafetyofLi-ionbatteriesdependsontheattributesof
systemdesign, suchaselectronics, estimationalgorithms,andthermalandmechanical characteristics,
147
Emerging Technologies for Electric and Hybrid Vehicles
- Titel
- Emerging Technologies for Electric and Hybrid Vehicles
- Herausgeber
- MDPI
- Ort
- Basel
- Datum
- 2017
- Sprache
- englisch
- Lizenz
- CC BY-NC-ND 4.0
- ISBN
- 978-3-03897-191-7
- Abmessungen
- 17.0 x 24.4 cm
- Seiten
- 376
- Schlagwörter
- electric vehicle, plug-in hybrid electric vehicle (PHEV), energy sources, energy management strategy, energy-storage system, charging technologies, control algorithms, battery, operating scenario, wireless power transfer (WPT)
- Kategorie
- Technik