Reactive Power Compasion Fianl Project Report.docx

Reactive Power Compasion Fianl Project Report.docx

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ReactivePowerCompasionFianlProjectReport

EE8110FianlProjectReport:

ReactivePowerCompensation

ByDehuaLaiTU#912747586

1.Introduction:

Overthelastfewyears,theinterestinreactivepowercompesationhasbeengrowing,mainlybecauseofthewayinwhichenergysupplierchargeacustomerforreactivepower.Moreover,theenergypriceisgrowing,whatforcetheindustryplantsandindividualcustomerstominimizeeneryconsumption,includingreativepower.Therearefewsulutions,thatallowhandletheproblemofreactivepowercompensation.ThetechnologiesimplementedwithStaticCapacitors,StaticVarCompensatorandStaticVarGeneratorareconciselypresents.Inthisreport,thesimulationandstudyforthesemethodsaremade.Ialsocomparethemeritsandfaultsofdifferentmethodsaftersimulation.ItisshownthattheSVGisevenmoreadvantageoustodynamicallyimprovevoltageregulation,stability,andpowerfactor.

1.1BasicPowerTheory

1.1.1ActivePower

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

a）

b）

c）

d）

Fig.11SimluatedharmonicmagnitudesofcurrentinaTCRfordifferentthyristorphase-shiftangles

2.2.3SimulationResultswithSVGcontrolledbytheinstantaneouscurrentdirectly:

Fig.12–Fig.21showthesimulationresultswithSVGvarcompensationcontrolledbytheinstantaneouscurrentdirectly.Allthe