电力电子 变频传动.docx

电力电子 变频传动.docx

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电力电子变频传动

HerbertStemmler

Chapter7

High-PowerIndustrialDrives

7.1Introduction

7.2ClassificationWithSpeedAndPowerRatings

7.3ShortReviewOfTheEvolutionOfLargeDrives

7.4MotorsForLargeDrives

7.5ConvertersForLargeDrives

7.6SynchronousMotors,FedByExternallyCommutatedCurrentSourceConverters

7.7InductionMotorsFedByCurrentSourceConverters

7.8TheCycloconverter-FedSynchronousMotor

7.9LargeVoltageSourceInverterDrives

7.10SlipPower-ControlledDrives

7.11Conclusion

Nomenclature

References

7.1.INTRODUCTION

Whenhigh-powerthyristorsforlargeconvertersandcontrolmethodsforACdriveswerereadyforuseattheendofthe1960s,largefrequency-controlledconverterscouldbebuilttomeettherequirementsforlargedriveswithadjustablespeed.Thisresultedinafirstbreakthroughforlargedrivesinindustrialapplicationsdurinethe1970s.

Theincentivetousevariablespeeddriveshasvariousreasons:

1.Thecostformaintenancecanbereducedandthelifetimeincreasedwhenmechanicalpartsinthedriveequipmentarereplacedbyfullystaticconverters.Inthecementindustry,gearlessmilltubeswithconverter-fedwrap-aroundACmotorinsteadofthegearareatypicalexampleforthissubstitution.

2.Largeinrushcurrentsofhigh-powermotorsandgeneratorsduringstart-upcanbeavoidedbysoftstartingviafrequencyconverters.Start-upconvertersforgasturbinegeneratorswereamongthefirstapplicationsofthistype.Heretheconvertersreplacedcomplicatedequipmentwithastartingmotor.

3.Cuttingenergyuseinpowerplants,chemical,andindustrialplantsbyreducinglossesintheprocessequipmentisbecomingmoreandmoreimportant.Inrotatingequipmentsuchaspumps,fans,blowers,andcompressors,muchenergyisthrownawaybycontrollingtheflowoffluidorgaswiththehelpofthrottlingvalves,dampers,andadjustableguidevans.Withadjustablespeeddrives,thisunnecessarydissipationcanbeeliminated[1].InmanyU.S.powerplants,existingfixedspeedmotorsthereforehavebeenretrofittedwithfrequencyconverters.

4.Thespeedoffrequency-controlledmotorsisnotlinkedto3000or3600rpmcorrespondingtotheACsystemfrequencies50or60Hz.Theycandrivehigh-speedcompressorsupto6000,10,000,oreven18,000rpm.

5.High-torque,low-speeddriveapplicationssuchasreversingrollingmillsinthesteelindustryorlargehoistsintheminingindustryisanotherfieldforlargedrives.

6.High-powerdrivesarealsonecessaryinseaandrailtransportsystemssuchaslargepassengerlinersorlocomotiveswithon-boarddieselgeneratororwithoverheadcontactwireforACorDCsupply.TheseapplicationsarenotdirectlyinthescopeofChapter7.They,however,willbementioned.

7.Fixedfrequency,variablespeedmachinesfedfromorfeedingintotheACsystemalsoneedlarge-frequencyconverters.Converter-controlledlargemotorgenerators,uptoabout400MW,inpumpedstoragehydropowerplantsarethemostrecentdevelopmentinthiscategoryofapplications.Inthegeneratingmode,energycanbesavedbyoperatingthemachineatthatspeed,wherethehydraulicefficiencyisatitsoptimum.Inthepumpingmode,loadcontrolcanbeachievedonlybyspeedcontrol.

Inthischapter,aftertheclassification（Section7.2）andashortreviewoftheevolution（Section7.3）,Sections7.4and7.5presentasurveyofthemotorsandconvertersusedforlargedrives.ThenthedifferentdrivesystemswhichbecameimportantinindustrialapplicationsaredescribedinSections7.6to7.10.Itisshownhowmotor,converter,andcontrolsformadrivesystem.Thespecificcharacteristicsofeachsystemareemphasizedinordertoshowwhichsystemisbestsuitedforwhichkindofapplications.Basedonthedevelopmentpotentialthepaperalsogivesaprojectionforthefuture.

7.2.CLASSIFICATIONWITHSPEEDANDPOWERRATINGS

Thepowerratingsoflargedrivesreachfromjustbelow1MWupto10MWandeven100MWandmoreinspecialcases.Theupperlimitisrathergivenbytherequirementsoftheapplicationsthanbythetechnologyoftheconvertersandmachines.

Themaximumspeedreachesfromabout10rpmforlow-speeddrivesupto1500or3000rpmfornormal-speeddrivesand6000and12,000rpmoreven18,000rpmforhigh-speedandvery-high-speeddrives.

Theattainablemaximumspeeddecreaseswithincreasingpowerratings.The10MW/6000rpmaretypicalratingsforhigh-power,high-speeddrives.Theattainablelimitratingscanroughlybemarkedbythefigures80MW/3000rpm,15MW/6000rpm,and3MW/18,000rpm.

7.3.SHORTREVIEWOFTHEEVOLUTIONOFLARGEDRIVES

Duringthe1960sline-commutated,controlledrectifiersusingnewhigh-powerturn-onthyristorssubstitutedforrotatingconvertersandmercuryarcvalveswhichhavebeenusedbeforetocontroltorqueandspeedoftheDCcollectormotors.Thiswasarealprogressattheconverterside:

afullystaticsolutionwithfewerauxiliaries,whichofferedahigherflexibilitywithrespecttotheapplications.Butthedisadvantagesatthemotorsidewerenotremoved:

duetotheirmechanicalcollector,DCmotorsarenotonlyexpensiveandsubjecttowear,butalsolimitedintheirratingstoabout1000V,1000rpm,1000kW（increasingofoneoftheseratingsmeansreductionoftheothers）.DCmotors,therefore,coveronlythelowestrangeoflargedrives.TheserestrictionscalledforACmotors.

Startinginthemiddleofthe1960s,everyeffortwasmadetodevelopACdrivesystemswithvariablefrequency.Newmodulationmethodssuchaspulsewidthmodulation（PWM）emerged[2],andnewcontrolmethodssuchasvectorcontrol[3]andfield-orientedcontrol[4,5]wereintroduced.Theseinvestigationsanddevelopmentsresultedinarealbreakthroughforlargedrivesinthe1970s.Avarietyofdifferentlarge-drivesystemswithspecificadvantagesopenedthewayfornewapplications.

Cycloconverter-fedsynchronousmotors,wellsuitedforlow-speeddriveswithhightorqueevenatstandstill,hadbeenthefirstlargeACdrivesofthisgeneration,whichwereputintocommercialoperationattheendofthe1960s.Theywereintroducedingearlesscementmilldrivesandhadalreadyanewvectorcontrol[6].Cycloconverter-fedsynchronousmotorsarenowstateoftheartforallkindsoflow-speedhigh-torquedrives（seeSection7.8）.

Innormal-andhigh-speeddrivesforallkindsofpumps,fans,blowers,andcompressorsandasstart-upequipmentforlargesychronousgeneratorsandmotors,thesynchronousmotorfedbyalineandmotor-commutatedcurrentsourceconverterbecamethemostsuccessfullarge-drivesystem.Itwasintroducedatthebeginningofthe1970smainlyasstart-upequipmentforgasturbinegenerators[7].Maximumspeedof6000rpmandpowerratingscloseto100MWarenowstateoftheart.（SeeSection7.6.）

Slipringmotorsfedbysubsynchronousconvertercascadeswithslippowerrecoverywereintroducedatthesametime.Theyarewellsuitedforalimitedspeedrangebetween70%and100%ofthesynchronousspeed.Thesmallerthespeedrange,thelowertheratedpowerforwhichtheconvertercascadehastobedesigned.Thissystemissuccessfulasalow-costdesignforapplicationswithreducedrequirements,wherepowertransferviaslipringsisacceptedandwhereauxiliariesforthestart-uptothenormalspeedrangecanbetolerated.Itsattractivitygoesdowninthesamedegreeasthecostofotherdrivesystemswithbettercharacteristicsdecreases.（SeeSection7.10.）

Slip-ringmotorswithsub-andhypersynchronouscascades,usingthree-phasecycloconvertersattheslipringside,foundonlyspecialapplicationswith,however,high-ratedpowerupto80MVApersingleunit.Especiallyin50-162/3Hzintertiestosupplythe162/3HzrailwaysysteminEurope,theywereusedsincethemiddleofthe1970satthe50Hzsidetodrivethesingle-phasesynchronousgeneratorsfeedingthe162/3Hzside.Suchintertiesarefrequencyelastic.Evenwithdeviationsofsomepercentageinthefrequencyofthe162/3Hzsystem,theycanbeoperatedwithoutrestrictions[8].Butthereisanewapplicationcomingupatastillhigherpowerlevelofsome100MWpersingleunit:

inpumpedstoragepowerplantswithextremevariationsoftheturbineheads,theoptimalhydraulicefficiencyatagivenheaddependsonthespeedoftheturbine.Thesystemiswellsuitedtooperatethegenerator,feedingthe50Hzor60Hzsystematvariablespeedofabout±10%or20%aroundthesynchronousspeed.Inadditionloadcontrolevenduringpumpingoperationcanbeachievedbyvaryingthespeed[9].（SeeSection7.10.）

Manyeffortshavebeenmadeduringthe1960sandthe1970stousethesimple,robust,andcheapinductionmotorforlargevariablespeeddrives.Butwhereasallthedrivesystemsmentionedabovecanbeoperatedwithlineorloadcommutatedconventionalturn-onthyristors,inductionmotorsneedinverters,thethyristo'rsofwhichcanbeturnedoff.Sinceturn-offthyristorshadnotbeenavailableatthattime,conventionalturn-onthyristorswithauxiliarycircuitsforforcedcommutationhadtobeused—acomplicatedandexpensivetechnology.Forced-commutatedturn-onthyristorswereusedinvoltagesourceandincurrentsourceinverters.

Becauseoftheircomplexitysuchforcedcommutatedvoltagesourceinvertersfeedinginductionmotorswereonlysuccessfullyusedinrailwayapplications.ThereitwasattractivetosubstitutethesmallerandsimplerinductionmotorfortheDCmotorinthenarrowspaceofthebogiesofthelocomotives[10,11].Evenwhenlarge-gateturn-offthyristors（GTOs）becameavailableinthefirsthalfofthe1980s,ittookuntiltheendofthe1980sbeforelargeinductionmotorsfedbyGTOinvertersweredeliveredfori