电力电子 变频传动.docx
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电力电子 变频传动.docx
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电力电子变频传动
J.D.vanWyk
Chapter3
PowerElectronicConvertersforDrives
3.1Introduction
3.2DevelopmentOfPowerElectronicConvertersanditsApplicationtoDriveTechnology
3.3SomeFunctionalConsiderationsRegardingSwitchingConvertersAndTheirApplicationstoVariableFrequencyDrives
3.4PowerElectronicConvertersforControlofAmplitude
3.5PowerElectronicConvertersforACVariableFrequencyDrives
3.6SwitchApplicationsTechnology
3.7FutureConverterDevelopmentinRelationtoElectromagnetics
3.8Conclusion
References
3.5.POWERELECTRONICCONVERTERSFORACVARIABLEFREQUENCYDRIVES
InSection3.3.4someoverallconverterstructuresforACvariablefrequencydriveswerediscussed.Themachine-commutatedinvertersaredescribedwellintheliterature[4,53]andwillnotbediscussedhere.However,anoverviewofthemanycompositeconvertersforvariablefrequencyPWMoperation—withchieflyinductionmachinesasloads,isstilldeemednecessary—particularlyinviewofthevariationsintopologyandstructurebroughtaboutbythequestforsupplyfriendlydrivesandsoftswitchingconvertersystemsathigherpowerlevels.Inthissectionthediscussionconcernsthetopologiesandstructures,whiletheconsiderationsregardingswitchingtechnologywillbeexaminedinSection3.6.
3.5.1.AC-DC-ACConvertersforCurrent-FedInverterDrives
Force-commutatedinvertertechnologystartedshortlyaftercontrolledmercuryarcrectifierscameintopractice[5],bothvoltage-fedandcurrent-fedtopologiesappearing.Afterthyristorsappeared,attentionfocusedinitiallyonthevoltage-fedtopology,andsubsequentlycurrent-fedinvertersreceivedattention[61],leadingtothedevelopmentofthewell-knownautosequcntiallycommutatedcurrent-fedinverter[62],whichhasfoundwidespreadpracticalapplication[53]andisdescribedadequatelyintextbooks[56].Figure3-19aindicatesthegenericstructureofthecurrent-fedAC-DC-ACconverters.Inindustrialandtractionapplicationsthesecurrent-fedAC-DC-ACconvertersarerobustinoperationandreliableduetotheinsensitivitytoshortcircuitsandanoisyenvironment.However,whetherappliedtosynchronousorinductionmachines,thepulsatingtorque(atsixtimestheinverterfrequency)deliveredbythedrivecanleadtomechanicalresonances,additionallosses,andotherproblems.InsubsequentdesignsitwasshownthatPWMoperationofthecurrent-fedinvertercanleadtoelimationofharmoniccurrentcomponents,causingtorqueoscillationsinthemachine[47],evenusingthyristorswithauto-sequentialforcedcommutation.TheavailabilityofBJTs,IGBTs,andGTOsfirstledtoreplacementoftheforcecommutated-thyristorswiththeadditionofasmallcapacitorfilterontheinductionmachineinputterminals[17,63],asshownontheinverterofFigure3-19b,greatlyimprovingthewaveformsofvoltageandcurrentappliedtothemachine,aswellaseasingturningoffofthedevicesintheinverter,sincequasi-sinusoidalPWMcouldnowbeappliedtotheinverteroutputcurrent.Thisalsosolvedthepulsatingtorqueproblemofthesedriveseffectively.However,current-fedinvertersneedsymmetricaldevicesasfarasblockingvoltageisconcerned,sothatforIGBTsandreverseconductingGTOs,aseriesdiodeisalwaysnecessary.Anaturalfollow-ontotheGTOcurrent-fedinverterwithcapacitorniterswastoaddasimilartopologytotheinput,leadingtothedoublePWMcurrent-fedstructureofFigure3-19b[63],representingthestate-of-the-artdevelopmentinthistechnology.
3.5.2.AC-DC-ACConvertersforVoltage-FedInverterDrives
Voltage-fedinverters,asdiscussedinrelationtoFigure3-16,havehadalineofdevelopmentcloselycoupledtotheavailabilityoftheappropriatepowersemiconductordevices.Althoughinprinciplethevoltage-fedinverterismorepronetoreliabilityproblemsinaharshenvironmentthanthecurrent-fedinverter(withsimultaneousconductionoftwodevicesinoneinverterlegbeingpotentiallythemostdangerous),protectionandcontrolschemesweredevelopedthatenabledreliableapplication.Voltage-fedinvertersdonotneedreverseblockingdevices,favoringthemoderndevicessuchasIGBTsandGTOs.
However,voltage-fedinvertersinforcedcommutationthyristortechnologydevelopedtoastagewhereitcouldbeapplieduptothehighestpowerlevelsinmainlineelectriclocomotives.Sincetheseconverterstructuresremainedcomplicatedduetotheadditionalcommutationcircuits,itwastheavailabilityofFETs,BJTs,andIGBTsthatsawtothesuccessfulpenetrationoftheentirepowerrangebythethree-phasedioderectifier-fed,PWMinverterdriveforinductionmachines,showninFigure3-19c[2].PWMtechnologyenabledeliminationofharmonicsfromtheinverteroutputvoltage,allowingquasi-sinusoidalmachinewaveformsandeliminatingtorquepulsations.Thecurrent-controlled,voltage-fedPWMinverterhasgraduallybeensupersedingcurrent-fedtechnologyoverthepastyears,especiallysincetheavailabilityofGTOsextendedtheapplicabilityofturn-offdevicesinvoltage-fedinvertersuptothehighestpowerlevels.
3.5.3.SupplyInteractionofAC-DC-ACConverters
Thesupplyinteractionhasremainedaproblemovertheentirepowerrange,sincetheinputconverteriscustomarilyanuncontrolledoracontrolledrectifierbridge(seeFigures3-15,3-16,and3-19).Thissupplyinteractioncouldbesolvedfortractionsystemsbythefour-quadrantconverterasdiscussedpreviouslyinrelationtoFigure3-18b,whileinthelowerpowerrangeofAC-DC-ACconvertersfedfromathree-phasebus,thesolutionofFigure3-18cprovidestheappropriateinputconverter.ThedoublePWMvoltage-fedstructureshowninFigure3-19d[64]representstheultimatepowerelectronicsolutionintermsofPWMvoltage-fedconvertertechnologyregardingasupply-friendlyandmachine-friendlyconvertersystem.Althoughthistypeofsystemcanbeimplementedusinganyofthepresentlyavailableturn-offdevices(FETs,BJTs,IGBTs),generalapplicationstillhastodevelop.
Thesupplyinteractionofcontrolledanduncontrolledrectifiershasbeenthesubjectofmuchworkinthepastandhasalreadybeentreatedextensivelyattextbooklevel[57,65,66]sinceawarenessoftheproblemhadbeenformulatedinthetimesofmercuryarcrectifiers[67].Itisonlyrecently,however,thatproliferationofAC-DC-ACconvertersfordrivesandotherpowerelectronicsequipmenthascausedseriousconcernonthegeneralproblemofnonlinearloadsonpowernetworks,givingrisetoproblemsregardingmodeling,measurement,andcompensationofsupplyinteraction[48].
Ofparticularinterestarethestandardsthathavecomeintobeinginternationallytocontrolharmonicproliferationfromconvertersinpowernetworks.Notably,IEEE-519regulatestheharmonicinjectionatthepointofcommoncoupling(PCC)andistargetedtowardlargerplantandequipment[68,69,70].IEC-555-2regulatestheharmonicemissionsfromeachpieceofequipmentconnectedtoanACsupplysystemandtargetsthesmallerrange(below15A,chiefly)[71].ItisthereforealreadyevidentthatsupplyinteractionofallAC-DC-ACconverter-feddrivesisgoingtobeacentralconsiderationinfuture,placingspecialemphasisonthedevelopmentofsolutionssuchasthoseofFigures3-18and3-19d.
3.5.4.MoreExtendedConverterFamilies
Theprecedingdiscussionshavebeenconcentratingontheclassicaltopologiesforsingularconvertersthathaveevolvedovertime.Inthecontextofconvertersfordrives,thisinevitablyevolvestowardsix-pulsetopologies.Thefieldofpowerconvertersfordrivesremainseverinteresting,sincemanypossiblevariantsofconvertertopologyandstructurecontinuetoexist—especiallyforspecializedapplications.Someofthesevariantsarediscussedinthissection.
Cycloconverters.Althoughtheseconvertershavebeenknownsincecontrolledswitchingdevicesbecameavailable[5],powersemiconductorsincreasedtheapplicationpossibilities.Figure3-20arepresentstheconverterstructurecomprisingthecombinationofnineACswitches[29],WiththeACswitchconsistingoftwoanti-parallelswitcheswithdelayablecontrol(suchasthyristors),thewell-knownnaturallycommutatedcycloconverter—aswidelyapplied—isobtained.However,sincetheadventofsimplerturn-offtechnologyinconverters,therehasbeenaquestfora"generalconverter"tocoupletwomultiphasesetsofACvoltagesbyhavingthenineACswitchescapableofturningonandoffatanyinstant[29-31].Applicationpossibilitieshaverecentlybeenproven[32],andthepowerlevelmightbeextendedinthefuture.
CompositeConverterswithSpecializedACLinks.Whenconsideringvoltage-fedinverters,thelinkhasgenerallybeenconsidered,first,tobeadirectvoltageoradirectcurrentlinkand,second,toconsistofpassiveelementsonly.Duringtheearlierstagesofthedevelopmentofthyristorforcedcommutationtechnology,severalschemestoactivelyreducetheDClinkvoltageorcurrenttozerobyemployingaswitchingelementinthelinkwereproposedandtried[51,52].Turningoffalltheelementsintheinverterbridgewasconsequentlyachieved.HybridBJT-thyristorinvertersweredeveloped,exhibitingthecharacteristicthatallswitchingtransitionscouldbeundertakenonlywhenthelinkwasactivated(and,forinstance,thelinkvoltagereversedorreducedtozero[72]).
Thenewgenerationofsoftswitchedtopologies,suchastheresonantDClinkinverters[73]andtheresonantAClinkconverter[74],developstheideaofactivelyusingthevoltagevariationsinthelinktostyletheturn-offofthedevicesintheconvertersfurther.Evenfurthermeasuresandactivedevicescanbeintroducedtoimpartthenecessarycharacteristicstotheconvert
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