SwitchingandNon-LinearSimpleSelectionofSwitchingNon-LinearElementsSwitchingandnon-linearelementsarethosethatchangestateduringasimulation,accordingtocertainconditions. Thesedevicescanrangefromsimpleswitchingelements,suchaspowerelectronicdevices,(i.e.thyristors,diodes,etc.),breakersandfaults,tomorecomplexnon-linearelementsthatcanhavemanystates,suchasthearrestor.塊，到更復(fù)雜的包含狀態(tài)的非線性元件，比如arrestor.Inadditiontothosewithmanystates,non-lineardevicescanalsobemodeledwithanadditionalcompensatingcurrentsourcethatcanbeprogrammedtorepresentanynon-linearity.的方法可以代替任意的非線件。SimpleThereareseveraldifferentmethodsforrepresentingasimpleswitchingelementintimesimulationprograms[5]. Themostaccurateapproachistorepresentthemasideal. Thatis,possessingbothazerointheONstateandaninfiniteintheOFFstate.值為理想器件。也就是說，在ON狀態(tài)時(shí)等值為0電阻，在OFF狀態(tài)時(shí)等值為無Althoughthisapproachisveryaccurateandtheresultingequationseasiertosolve,thedrawbackisthatmanypossiblestatesarecreated,whichmusteachberepresentedbydifferentsystemEXAMPLE3-3-ConsiderthenetworkofFigure3-3andletthe representasimpleswitch. IfR12wereconsideredideal,thentwodifferentnetworkscouldresult,dependingonthestateofthe ThisisillustratedinFigure3-4:3-4Nowimagineforinstance,anetworkcontainingmanyswitches(asina48-pulseGraetz ),agreatnumberofdifferentnetworkconfigurationswouldresultifidealswitchingelementswere基于實(shí)際，考慮一個(gè)包含眾多開關(guān)器件的網(wǎng)絡(luò)（48Graetz），InEMTDC,simpleswitchingdevicesarerepresentedasavariableresistor,possessinganONandanOFF Althoughthistypeofrepresentationinvolvesanapproximationofboththezero(ON)andaninfinite(OFF)ofanidealswitch,itisadvantageousinthatthesamecircuitstructurecanbemaintained,andtheelectricnetworkwillnotneedtobesplitintomultiplenetworks,asaresultofeachswitchingevent.在EMTDC中，簡單的開關(guān)裝置被等值為變化的電阻，有開電阻和關(guān)斷電阻兩種狀態(tài)。雖然這種等值近似于等值為0電阻和無窮大電阻，但每次開關(guān)發(fā)生SelectionofSwitchingInEMTDC,thereareprovisionstoallowforzeros(seeIdealBranches). However,whiletheidealbranchalgorithmisveryreliableandgivesthetheoreticalresult,itdoesinvolveextracomputationstoavoidadivisionbyzerowheninvertingtheconductancematrix. Thus,byinsertingareasonabletypicalofaclosedswitch,youcanimprovethesimulationspeed. non-zerovaluelargerthan0.0005shouldbeusedwhereverEMTDC，0G0值可以提真速度。任意的非零且大于0.0005歐姆的值在任何可能的情況下Selectionoftheswitchingsisimportant: Iftheistoosmall,itsvaluemaydominatetheconductancematrixandtheotherdiagonalelementscouldbeovershadowed Thiswillcauseitseffectiveconductancematrixinversiontobeinaccurate. ThedefaultON valueinPSCADis0.001. threshold,underwhichtheIdealBranchalgorithmwillbeinvoked,is0.0005.Branch算啟動(dòng).TheseimportantfactorsshouldbekeptinmindwhenchoosingaswitchCircuitlossesshouldnotbesignificantlyCircuitdamshouldnotbereducedsignificantly: Duetothesolutionbeinginstepsofdiscretetimeintervals,numericalerrormaycreatelessdaminthecircuitthanexpectedinreality. Asmallamountofadditionalfromaclosedswitch,ifjudiciouslyselected,maycompensatethenegativedameffectinthesolutionmethod.實(shí)際電路更少的阻尼。明智地為關(guān)斷的開關(guān)選擇較少增加電阻，或以補(bǔ)償Non-LinearTherearetwomethodsforrepresentingnon-linearelementsin ThePiecewiseLinear,andtheCompensatingCurrentSource Eachmethodpossessesitsownprosandcons,andtheselectionofeitherissimplyuptotheuser.ThePiecewiseLinearAlthoughanon-lineardevicemaypossessacharacteristicthatiscontinuous,controllingthedeviceascontinuousisnot Continuallychangingbranchconductancecanaconductancematrixinversioneverytimestep,resultinginasubstantiallylongerruntimeinlargenetworks.雖然非線件可能擁有續(xù)的特性曲線，但不推薦把它當(dāng)做連續(xù)的來管Figure3-5-(a)Continuous (b)PiecewiselinearconductanceInordertominimizeruntime,aPiecewiseLinearapproximationmethodasillustratedinFigure3-5(a)and(b)isused. piecewiselinearcurvewillintroduceseveral'stateranges'intothenon-linearcharacteristic,dramaticallyreducingtheamountofmatrixinversionsperrun,yetmaintainingreasonableaccuracy.為了減小仿真時(shí)間，使用了圖3-5說明的一種分段線性化的方法。分段線性化InEMTDC,non-lineardevices,suchastheArrestorcomponent,utilizethePiecewiseLineartechnique.EMTDCArrestorCompensatingCurrentSourceAnothermethodtomodelinganon-linearcharacteristicisthroughtheuseofacompensatingcurrentsource. ThistechniqueisplishedbyaddinganequivalentNortoncurrentsourceinparallelwiththedeviceitself,therebyallowingfortheadditionorsubtractionofextracurrentatthedevicebranchnodes.Figure3-6-CompensatingCurrentSourceMethodCaremustbetakenwhenusingthismethodtomodeldevicenon-asanopencircuittovoltagesinthepresenttimethereby Moreoftenthannot,thecompensatingsourceasanopencircuittovoltagesinthepresenttimethereby Thiscreatede-stabilizationproblemsinthesimulation[5]. circumventthisproblem,thecompensatingcurrentsourceshouldbeusedinconjunctionwithacorrectionsou