中英文翻译Word格式.docx
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Itisimportanttoeliminatethevoltagefastvariationsbecausetheyarethemostfrequentlycauseofdisruptedoperationsformanyindustrialprocesses,particularlythoseusingmodernelectronicequipment,whicharehighlysensitivetoshortdurationsourcevariations[2].
DynamicVoltageRestorer(DVR)andUninterruptedPowerSupply(UPS)systemshadbeenresearchedanddevelopedalongthelastdecadesandtheyarecapabletocompensatevoltagesagsandswells.Nevertheless,theydependondevicestostoreenergy,likelargecapacitorsorbatteriesbank.Thenominalpoweroperationisafunctionofsizeandcapacityofthosedevices;
ifthepowerisincreased,thesizeofthedeviceswillincrease.Inspiteoftheabove,theUPSsystemsarecapabletosupportenergyinterruptions.
Otheroptiondeveloped,whichisabletocompensatevoltagesagsisbasedonPWMAC-ACconverter[3],[4].Thissolutionusesanautotransformercomposedbyoneprimarysideandtwosecondarywindingspresentingagoodperformance.Thesystemcompensatesuntil50%voltagesagsandswellsandcancontinuouslyshapetheoutputvoltagetobesinusoidal(withlowTHD).Nevertheless,theautotransformerdrivesalltheloadpowerduetoitisconnectedbetweentheloadandtheACmains.
InthispaperaPWMAC-ACconverterispresented,inordertocompensatevoltagesagsandswellssimultaneouslyincriticalloads,andtomaintainacontinuousregulationintheoutputvoltage.Thesystemconsistsinasingle-phaseAC-ACconverterinamatrixarrangement,andenergystoragedevicesarenotrequired.AfourstepswitchingtechniqueisusedtodriveAC-ACconverterswitches,executingsnubber-lessoperations.Thereferencesignalisgeneratedusingsingle-phased-qtheory,obtainingafastresponsetimeandcontinueregulation,withahighefficiency.
Oneoftheadvantagesinthisstructureisthatthetapsofthecouplingtransformerarenotrequiredtochangethepolarityofthecompensationvoltage,andtheconverterdrivesonlyapercentoftheloadpower.
Design,constructionandperformancearedetailed,andseveralsimulationsandexperimentalresultsobtainedwithalaboratoryprototypeareshowedtovalidatetheapproach.
II.CONVERTERANALYSIS
ThestructureoftheproposedapproachisshowninFig.1.
Fig.lConceptualdesignoftheproposedapproach
ItsprincipalobjectiveconsistsinsupplyacompensationvoltageinordertokeepalwaysthenominalvalueoftheACmains.Whenvoltagesagoccurs,theconvertersuppliesthenecessaryvoltagetomaintainregulationintheoutputvoltage.Inthesameway,whenvoltageswelloccurs,theconverterreproducesthenecessaryvoltagetocanceloutthe
overvoltage.
Thetopologyofthesingle-phaseAC-ACconverterisshowninFig.2.
Fig.2Single-PhaseAC-ACconverter
Theconverterhasthefollowingelements:
Fourcurrentandvoltagebi-directionalswitchingdevicesconnectedtotheACmains[5],[6],[7].
Twolow-passfilterstoreducethehighfrequencyassociatedtoswitchingininputcurrentandoutputvoltage[8].
TheAC-ACconvertergeneratesaPWMACvoltagetocancelthe
variationsintheACmainsandtocompensatethevoltagesagsandswells.
S1,S2,S3andS4areusedtogeneratethePWMvoltagewiththepolarity
required.Theadequateoperationoftheswitchesallowsproducingan
outputvoltageVoutonphaseor180°
phase-shiftedwithrespecttoVin.
Whentheutilityvoltageisatnormallevel,theswitchesS3and
S4areclosed(orS1andS2)andtheoutputvoltageisequaltozero.When
thereisavoltagesag,theswitchS4isclosed,andS1andS3areoperated
withadutycycleD,generatingaVout,forcompensation.Whenthereis
avoltageswell,theswitchS3isclosed,andS2andS3generateaVout,
withapolarityinvertedforcompensation.SwitchesS1-S3andS2-S4
nevershouldbeclosedatthesametimeinordertoavoidashort-circuit
intheACmainsside.
Theswitchesaredrivenusingasignalpatternwhichincorporatea
four-stepswitchingstrategy,reducingtheswitchinglossesand
eliminatingtheuseofsnubberscircuits.
III.MODULATIONTECHNIQUE
Thefunctionofthesingle-phaseAC-ACconverteristoreproducea
voltagewithapeakamplitudelowerorequalthantheACmainsvalue.Toachievethis,thevoltageoftheACmainsismodulatedbyusingaswitchingpattern.Theamplitudeofthefundamentalvoltagewilldependonthe
modulationindexoftheswitchingpattern.
Fig.3showstheschemeusedtoobtainapulsedpattern.Inthis
case,itisusedaDigitalSignalProcessor(DSP)togeneratethedutycycleDandtocontrolthePWMoftheswitchingdevices.
Theoperationmodeoftheschemeconsistsintoobtainareference
signalthatrepresentsthecompensationvoltageVc.Inthiscase,itis
usedthed-qtheorytotransformtheACmainsvoltageinaDCsignal.The
dcomponentiscomparedwiththenominalpeakvoltageoftheACmains
Vnom,toobtaintheVc.(Thed-qtheoryisexplainedinsectionIV).
Fig.3Schemetogeneratethecontrolpulses
TheC(s)controllercalculatesthedutycycleDfromVcandtheControllogicdetermineswhichoftheAC-ACconverterswitcheswillbeturnedonandwhichbeturnedoff(S1,S2,S3orS4).
TheswitchingpatternisobtainedwhenDandasaw-toothsignalgeneratedbytheDSParecompared.
A.Switchingpatternanalysis
Itispossibletodeterminetheharmoniccontentoftheconverter
outputvoltageVpwmfromtheanalysisoftheswitchingpattern.Thesamplingprocesstheoryisusedtoknowtheamplitudeandfrequencyofeachharmonicgeneratedintheconverteroutput.TherepresentationoftheswitchingpatterninFourierseriesisgivenby
(1):
(1)
Expressing
(1)incomplexform:
(2)
TheFouriercomplexcoefficientsoftheswitchingpatternarecalculatedusingequation(3).
(3)
ConsideringthattheswitchingpatternhasanamplitudeVxandthatthepulsewidthisx:
(4)
Equation(5)permitstoknowtheamplitudeandfrequencyoftheharmonicsandtherefore,toproposethecut-offfrequencyofthelow-passfilters.Inthiscase,itisjustnecessarytomultiplythemagnitudeof(4)bytheamplitudeoftheACmains.
(5)
where:
Ah=Harmonicsmagnitude.
A=ACmainsvoltageamplitude.
Vx=Commutationpatternamplitude.
x=Pulsewidth.
T=Commutationpatternperiod.
m=0,±
1,±
2,±
3,.....
ws=Switchingfrequency.
Oncecalculatedtheamplitudeandfrequencyoftheharmonics,thecut-offfrequencyofthelow-passfiltersisselected.ItisnotedthattheoutputvoltageintheAC-ACconverterdependsontheaveragedutycycleD:
(6)
Inthesameform,Disrelatedwiththecompensationandregulationoftheloadvoltage:
(7)
Thedutycycleisaffectedbytherelationoftransformationnofthecouplingtransformerselected.Inthiscase,itischosenabucktransformer,suchthatcurrentoftheAC-ACconverterwillbelowerthancurrentflowingthroughtheACmains.TheequationthatdeterminesDvalue
inopenloopisasfollows:
(8)
WhereVnomisthepeakofreferencevoltageandVdDQisthepeakvoltagerelatedtothesingle-phased-qtransformationofVin.Equation(8)showsthatVnom>
VdDQforavoltagesagandVnom<
VdDQforavoltageswell.ThisallowsthatDstayswithin1y-1.
B.Fourstepswitchingtechnique
Thefourstepswitchingtechniqueoffersasafetransitionofinductiveloadcurrentfromonebi-directionalswitchtoanother,andensuresasafePWMoperation.Thistechniquecontrolsindependentlyeachswitchingdevicewithinabi-directionalswitchelementthatdependsontheinputvoltageandloadcurrentpolarity.
InthecaseoftheAC-ACconverter,operationstateofS1,S2,S3andS4willdependontheinputvoltagepolarity,thecompensationtorealize(asagorswell)andthecontrolsignaloftheswitchingdevices.
ThediagramoftheoperationsequenceforvoltagesagsisshowninFig.4.TocompensateaswellitisjustnecessarytochangeS1byS3and