Reactive Power Compasion Fianl Project ReportWord下载.docx
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Powerisameasureofenergyofenergyperunittime.Ageneralwayofcalculatingpowerisastheproductofcurrentandvoltage;
foraresistiveelement,wecanapplyOhm’slaw.
1.1.2ComplexPower
Applyingthesimpleformula
becomesmoreproblematicwhenvoltageandcurrentarechangingovertime,astheydoina.c.systems.Inthemostconcisebutabstractnotation,power,current,andvoltageareallcomplexquatities,andtheequationforpowerbecomes
WhereSistheapparentpower.
1.1.3ReactivePower
Nowwealsospecifywhatwemightintuitivelythinkofasthedifferencebetweenapparentandrealpower,namely,reactivepower.Reactivepoweristhecomponentofpowerthatosillatesbackandforththroughthelines,beingexchangedbetweenelectricandmagneticfieldsandnotgettingdissipated.ItisdenotedbythesymbolQ,anditsmagnitudeisgivenby
Again,notehowtheequationconveragesfortheresistivecasewhare
and
astherewillbenoreactivepoweratall.ReactivepowerismeasuredinVAR,forvolt-amperereactive.Wecanrepresentpowerasavectorinthecomplexplane:
namely,andarrowoflengthS(apparentpower)thatmakesananglefwiththerealaxis.Thisisshowninfigurebelow.Theangle
isthesameasthephasedifferencebetweenvoltageandcurrent.
Fig.1Powertriangle
1.2Receiversandsourcesofreactivepower
Itiscommon,thatdeviceswhichconsumethereactiveinductivecurrentarecalledreactivepowerreceivers,whiledevicesconsumingreativecapacitivecurrentarereferredtoasreactivepowersources.
Mostoftheidustrialequipmentconsumesreactivepower.Thesedevicesareelectricmotors,transformers,conductors,chokes,converters,arcfurnacesandpowerelectronics.Inrandomcircuitwithoutsource,thereactivepowerisassosiatedwiththefraquencyandthepeakvalueoftheenergystoredperiodicallywithinmagneticandelectricfieldoftheelementsofthecircuit.Thereactivepowerofinductiveandcapacitiveelements,
and
respectively,canbeexpressedas:
Where
and
arethemaximumvalueoftheenergystoredinthemagneticfieldoftheinductiveelementsofthecircuitandelectricfieldofthecapacitiveelements.
Basingonthelawofconservationofenergy,theinputreactivepowerinthesource–lesscircuitisequaltoalgebraicsumofreactivepoweroftheinductiveandcapacitiveelementsincludedinacircuit,thatis:
Consideringanyelectriccircuit,oneknows,thatthegeneratedreactiveenergyisequaltotheconsumedenergy.Accordingtothis,thatmostoftheloadsintheindustryaretheloadsthatneedsinductivereactiveenergytooperate.Forthisreason,thereactivepowerdamandismuchmorethanthegeneratorisabletoproduce.Therefore,therearedevicesthatneedtobeconnectedtothesysteminordertoprovideanextrasourceofinductivereactivepowerordeviceswhichwillabsorbcapacitivepower.Thesetypesofdevicesare:
capacitorbanks,synchronousmotors,andpowerelectronicsourcesofreactivepower.Thecoopertationofcompensatingdeviceswithlinearcircuitscausesthereactivecomponentofthesupplyingcurrenttodecrease.
1.3ReactivePowerCompensationPrinciples
Thesourceofreactivepower(vars)containssynchronouscondensersvar,staticcapacitorsvar,staticvarcompensatorandstaticvergenerator.
Synchronouscondensershaveplayedamajorroleinvoltageandreactivepowercontrolformorethan50years.However,theyarerarelyusedtodaybecausetheyrequiresubstantialfoundationsandasignificantamountofstartingandprotectiveequipment.Moreover,theycannotbecontrolledfastenoughtocompensateforrapidloadchanges.Therefore,synchronouscondensersarenotpresentedinthisreport.
1.3.1Shuntcapacitor
Shuntcapacitorswerefirstemployedforpowerfactorcorrectionin1914.Theleadingcurrentdrawnbytheshuntcapacitorscompensatesthelaggingcurrentdrawnbytheload.
1.3.2StaticVarCompensator–SVC
SVCsconsistofstandardreactivepowershuntelements(reactorsandcapacitors)whicharecontrolledtoproviderapidandvariablereactivepower.Theycanbegroupedintotwobasiccategories,theTSCandTCR.
ThestaticcompensatoroftheTCRtypeincludeafixedcapacitorandafilterforloworder
1.3.3StaticGenetator–SVG
Inthelastdecade,alargenumberofdiffernetStaticVarGeneratorsusingpowerelectronictechnologieshavebeenproposedanddeveloped.TheaimofachievingdynamicalcompensationhasbeenfulfilledwithSVGsbutwiththeadvantageoffasterresponsetimes.SVGscontroloutputvoltagephase,adjustreactivepowercontinuouslyfromcapacitivetoinductive,suppressvoltagefluctuationandincreasesystemstability.
TheSVGisbasedonasolid-statevoltagesource,implementedwithaninverterandconnectedinparalleltothepowersystemthroughacouplingreactor.Theinverterismadeupfromaseriesofinverterswiththeirownisolateddcbus,whichmaybedcvoltagesourceordccurrentsource.Actually,thedcsourceisalwaystheDCcapacitorvoltage.
Therearetwobasicallydiffernetcontrolmethodsbothcurrentdirectandcurrentindirect.Currentindirectmethodgeneratedbalancedsetofthreesinusoidalvoltagesatthefundamentalfrequency,withcontrollableamplitudeandphase-shiftangle.CurrentdirectmethodbasedonPWMsystem.Bycontrollingtheinstantaneouscurrentdirectly,asetofPWMsignalscanbeproduced,thenthefrequency,amplitude,andphaseoftheacvoltagecanbemodifiedwiththeseadequatecontrolPWMsignals.
2Results:
Matlabpowersystemtoolboxsoftwareisusedtosimulatethepowersystem.Inthisreport,thesimulationmodesforshuntcapacitor,TCRandSVGcurrentdirectcontrolaredesigned.ThepresentedsimulationresultswereobtainedbyusingMatlab7.1.
2.1SimulationFigures
2.1.1BlockDiagramofShuntCapacitor:
BlockdiagramofshuntcapacitorreactivepowercompensationisshowninFig.2
2.1.2
Fig.2Blockdiagramofshuntcapacitorreactivepowercompensation
VS1isACvoltagesource,whosePeakamplitudeis312VandFrequencyis50Hz.Zisthenonlinearload.AndLis0.1HandRis18.25Ohm.Ctheshuntcapacitoris50uF.FFTisFastFourierTransformAlgorithm.
2.1.3BlockDiagramfotheTCR:
Fig3showstheschemeofastaticcompensatoroftheTCR.Itisthesingle-phase,includedaninductorL,andthethyristorTh1andTh2,whoarereverseparallelshunted.Reactorsarephase-anglecontrolled.
Fig.3BlockdiagramoftheTCR
InFig.3,VS1isACvoltagesource,whosePeakamplitudeis312VandFrequencyis50Hz;
Zisthenonlinearload,whoseLandRare0.1Hand18.25Ohm;
Reactorismadefromacapacitorandainductance,whoseCandLare120uFand0.02H;
@controlsphase-angle
.
2.1.4BlockDiagramoftheSVGControlledbytheInstantaneousCurrentDirectly:
Fig.4showstheschemeofthree-phaseSVGsystem.
Fig.4BlockdiagramoftheSVGcontrolledbytheinstantaneouscurrentdirectly
InFig.4theSVGsystemisfoundedonthebasicprincipleoftheabc-dq0tranformationmatrix.Itiscontrolledbytheinstantaneouscurrentdirectly,andthedcsourceistheDCcapacitorvoltage.ThePeakamplitudeandFrequencyofthree-phaseare312Vand50Hz.ThecapacitorCoftheDCvoltageis1410
.Thereferencedcurrent
andthefeedbackformthe
arealltheDCcurrent.RepeatingSequencegeneratedasignal.Thefrequencyofthesignalis20KHz,andtheamplitudeisfrom0to1.Asshown,therealsoisadistortedvoltagesource.
2.2SimulationResults
2.2.1SimulationResultswithshuntedcapacitor:
Fig5toFig.8showthesimulationresultswithshuntedcapacitorvarcompensation.
Fig.5simulatedvoltageandcurrentwaveformswithoutvarcompensation
Fig.6simulatedvoltageandcurrentwaveformswithshutedcapacitorvarcompensation
Fig.8Simulatedharmonicmagnitudesofcurrentwithshuntedcapacitorvarcompensation
Fig.7Simulatedharmonicmagnitudesofcurrentwithoutvarcompensation
2.2.2SimulationResultswithTCR:
Fig.9showsthesimulationresultsofcurrentaftercompensation.Inordertosimulatearealcasedistortionlevel,theallcurrentaremeasuredwithaharmonicanalyzer,asshowninFig.10
Fig.9Simulatedvoltageandcurrentwaveformswithoutvarcompensation
a)
b)
c)
d)
Fig.10SumulatedvoltageandcurrentwaveformsinaTCRfordifferentthyristorphase-shiftangles
b)
c)
Fig.11SimluatedharmonicmagnitudesofcurrentinaTCRfordifferentthyristorphase-shiftangles
2.2.3SimulationResultswithSVGcontrolledbytheinstantaneouscurrentdirectly:
Fig.12–Fig.21showthesimulationresultswithSVGvarcompensationcontrolledbytheinstantaneouscurrentdirectly.Allthe
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