外文文献翻译.docx

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外文文献翻译

外文文献翻译

专业

电气工程及其自动化

学生姓名

陈嘉俐

班级

BD电气071

学号

0720601103

指导教师

胡国文

电气工程学院

CompensationofVoltageSagsandSwellsusing

aSingle-PhaseAC-ACConverter

Abstract-Inthispaper,atopologytocompensatevoltagesagsandswellssimultaneouslyincriticalloadsisproposed.Itconsistsinasingle-phaseAC-ACconverterinamatrixarrangement,whichkeepsacontinuousregulationintheoutputvoltage.Theproposedschemehasthecapabilitytocompensateupto25%voltagesagsand50%voltageswells.

EnergystoragedevicesarenotrequiredbytheAC-ACconverteranditisconnectedbetweentheACmainsandtheloadbyusingaseriestransformer.Oneoftheadvantagesofthistopologyisthattapsforthecouplingtransformerarenonecessarytochangethepolarityofthecompensationvoltage.AfourstepswitchingtechniqueisusedtodrivetheAC-ACconverterswitches,executingsnubber-lessoperation.Thereferencesignalisgeneratedusingsingle-phased-qtheory,obtainingafastresponsetimeandhighregulation.

Simulationandexperimentalresultsofa5kWcapacity,127V,60Hzequipmentarepresented.

I.INTRODUCTION

ThequalityoftheACmainshasbeenaffectedbytheuseofnewsemiconductor-devicestechnologies.Nowadays,itiscommontofinddisturbancesintheamplitudeorwaveformshapeofcurrentandvoltageintheelectricsystems.Theseconditionscouldproducefailsintheequipments,raisingthepossibilityofanenergyinterruption.ThevoltagefastvariationsthatappearintheACmainsduring10secondsorlessarecommonlyknownasvoltagesagsandswells.Thesevariationsareproducedbynormaloperationofhighpowerloadsaswellastheirsconnectionanddisconnection;thevoltagefastvariationeffectsarefunctionoftheamplitudeandthedurationoftheevent.Somestudiesshowthat92%ofalldisturbancesintheelectricalpowerdistributionsystemsareproducedbyvoltagesags[1].

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

B.Fourstepswitchingtechnique

Thefourstepswitchingtechniqueoffersasafetransitionofinductiveloadcurrentfromonebi-directionalswitchtoanother,andensuresasafePWMoperation.Thistechniquecontrolsindependentlyeachswitchingdevicewithinabi-directionalswitchelementthatdependsontheinputvoltageandloadcurrentpolarity.

InthecaseoftheAC-ACconverter,operationstateofS1,S2,S3andS4willdependontheinputvoltagepolarity,thecompensationtorealize（asagorswell）andthecontrolsignaloftheswitchingdevices.

Thediagramoftheoperationsequenceforvo