sensorless initial rotor position estimation of surface PMSM

SensorlessInitialRotorPositionEstimation

ofSurfacePermanent-Magnet

SynchronousMotor

ShinNakashima,YuyaInagaki,andIchiroMiki,Member,IEEE

Abstract—Thispaperpresentsamethodofestimatingtheinitialrotorpositionofasurfacepermanent-magnetsynchronousmotorwithoutapositionsensor.Theestimationisperformedbyusingthenonlinearmagnetizationcharacteristicsofthestatorcorecausedbythemagnetoftherotor.Thismethodisbasedontheprinciplethatthe

NAKASHIMAetal.:ROTORPOSITIONESTIMATIONOFSURFACEPMSM1599

Fig.2.Measuredcurrents.(a)u-phasecurrents.(b)v-phasecurrents.(c)w-phasecurrents.(d)DifferencebetweenIj.

Fig.2showsthemeasuredphasecurrentswhentheconstantvoltagevectorsareappliedtothestatorwindingofthetestmotor

showninFig.2(a)isthe(seeSectionIII-A).Thecurrent

measured

-phasewindingisappliedtothemotor,andisalsothemeasured

-phasewinding.Fig.2(b)and

(c)isobtainedfromsimilarexperiments.Inthisfigure,theneg-toeasilyativecurrents

comparewiththepositivecurrents

isshowninFig.2(d).Asisobvious

fromFig.2,thedifferencebetweenthepositiveandthenega-tivecurrentsisabout0.1Aaroundthepointswherethe

isappliedtothemotor,if

-axiscur-the

thatisinitiallysettozero,rent

-axiscurrentandthevoltage_angleistheestimated

.Asthevoltagevectorapproachestheangle

-axiscurrentcanbeobtained

andtheangleofthe

-axiscur-rentisobserved.Theestimationerrormustbesmallerthan

,

areprovidedtothemotorbasedon

is7.5theresultofthefirstprocess.Theinitialvalueof

electricaldegrees,therefore,thesevoltagevectorsareapplied

,electricalinthedirectionof

degrees,asshowninFig.5.Thevoltagevector14equalsthe

inthefirstprocess.Thenewestimatedvectorgiving

-polepositioncanbeobtainedbythesameangle

wayasthefirstprocessforthesevoltagevectors.Accordingly,theaccuracyoftheestimatedangleis

istheoneofthe

voltagevectorshowninFig.4and

.

Inthefirstprocess,12distinctvoltagevectorsareprovidedtothemotorinnumericalorder(

-axiscurrenttransformedfromthe

three-phasecurrentsismeasured.Everytimethevoltagevectorisprovidedfor200

stoforceeachphasecurrentzero.Therotor

positionisestimatedusingthese

-axiscurrentequalsthefinalestimated

angle.

Sincethepositionofthemagneticpoleisestimatedbyusingthecurrentresponseforthevoltagevectorprovidedfromthe

1600IEEETRANSACTIONSONINDUSTRYAPPLICATIONS,VOL.36,NO.6,NOVEMBER/DECEMBER2000

Fig.3.Flowchart.

inverter,thismethodisnotaffectedbytheseterrorsandthevariationofthemotorparameters.Thetheoreticalmaximumac-curacyoftherotorpositionangleestimatedbythismethodis

NAKASHIMAetal.:ROTORPOSITIONESTIMATIONOFSURFACEPMSMFig.8.Measuredcurrents.

sourcevoltage

andtoimplementthees-timationwithoutrotatingtherotor.TableIshowssomemea-sured

issetto0electricaldegrees.In

thistable,

is0.57and

-axiscurrentmeasuredforvariousvoltagevectors

under

is90electricalde-grees.Asshowninthisfigure,the

1601

issetto0electricaldegrees.Fig.10(a)showsthe

-axiscurrent

14

7.5,0,

and7.5electricaldegreesisprovidedtothemotor.AsshowninFig.10(b),thenewmaximum

poleof

therotorisprovided.Therefore,thenewestimatedangle

canbe

obtainedforthevoltagevector17.Afterall,

issetto279and90electricaldegrees,respectively.Asisob-viousfromFigs.11(a)and4,

is270electricaldegrees.Inthesecondprocess,

,asshowninFig.11(b).

Therefore,thevoltagevectors19,20,and21areprovidedinthedirectionof

3.8electricaldegrees,andthemaximumestimationerrorwas18.75electricaldegrees.Themaximumerroris

observedneartheonlyonepointwhere

is180electricaldegrees.Themeasuredeachphasecurrentand

isfixedat180electrical

degrees.Althoughthe

-axis

currentat180electricaldegreesislessthanthatat150and210electricaldegrees.Therefore,theestimationfailedinthefirstprocessat

1602IEEETRANSACTIONSONINDUSTRYAPPLICATIONS,VOL.36,NO.6,NOVEMBER/DECEMBER2000

TABLEI

MEASUREDU-PHASECURRENTS

Fig.9.Experimentalsystem.

Fig.10.Estimationresultwhentheactualangleis0electricaldegrees.(a)d-axiscurrentinthefirstprocess.(b)d-axiscurrentinthesecondprocess.

consideredthatthisiscausedbytheinherentrotorstructureofthetestmotorandisaspecialcase.

IV.CONCLUSION

AnewinitialrotorpositionestimationmethodofsurfacePMSMwithoutapositionsensorhasbeenproposed.Thismethodisperformedbasedonthe

NAKASHIMAetal.:ROTORPOSITIONESTIMATIONOFSURFACEPMSM1603

Fig.13.Estimationresults.

Fig.14.Measuredcurrents.

thevoltagevectorappliedtothemotor,andusesthemagneticsaturationofthestatorcore.Duringtheestimationprocess,therotorispracticallyatstandstill,andtheestimationiscompletedwithinabout17ms.Accordingtoexperimentalresults,theaverageoftheestimationerroris