英文-利用高性能同时采样ADC降低高级电力线监测系统的成本

MaximAppNotesA/DandD/AConversion/SamplingCircuitsResourceSmart:GreenDesignKeywords:simultaneoussampling,ADCs,power-linemonitoring,smartgrid,analog-to-digitalconverter,three-phase,single-phase,multi-channel,supervisorycontrolanddataacquisition,SCADA,EuropeanUnion,EN50160,IEC62053,IEC61850,phaseadjustmentSep28,2009APPLICATIONNOTE4595Reducesystemcostforadvancedpowerlinemonitoringbyleveraginghigh-performance,simultaneous-samplingADCsBy:MartinMason,Director,PrecisionADCsAbstract:Risingpowerdemandsandafocusonenergyconservationaredrivingincreasedinvestmentintheglobalpower-deliveryinfrastructure.Asaresult,advancedpowerlinemonitoringsystemshavebecomeacriticalelementofthenewsmartgridsforbothsingle-andmultiphaseapplications.Withsystemperformancerequirementsgrowingmorestringent,designersareturningtosimultaneous-sampling,multichannel,high-performanceADCsfortheirpowerlinemonitoringormultichannelSCADA(supervisorycontrolanddataacquisition)systems.ThisarticlewasalsofeaturedinMaxim'sEngineeringJournal,vol.67(PDF,1.65MB).AsimilararticleappearedontheEDNMagazinewebsiteonAugust18,2009.IntroductionAdvancedpowerlinemonitoringsystemscombinepower-supplymonitoring,loadbalancing,protection,andmeteringfunctionsinonesystem.Thisapproachallowsthepowerutilitiestodeliver,andthecustomerstoconsume,gridpowermoreefficiently.Alongwithefficientdelivery,theadvancedpowerlinemonitoringsystemspredictmaintenanceneeds;detectandrespondtofaultconditions;recordandallowfordynamicloadbalancingandenergyconservation;monitor(andcontrol)thequalityofpowerdelivery;andhelpprotectequipment.Toimplementthesemonitoringsystems,ADCs(analog-to-digitalconverters)areneededtomonitorthevoltageandcurrentonmultiplephases.However,tomeetthestringentrequirementsofthevariousstandardsandtomeasureandoptimizepower-factorlosses,theseconvertersmustbesynchronizedtoensurethattheysamplethreephases(plusneutral)simultaneously.Synchronizingindividualconverterscanbedifficult,sovendorsoffermultiplesimultaneous-samplingADCsinasinglepackage.Ifamorehighlyintegratedsolutionisneeded,anotheroptionistointegratethesimultaneous-samplingconvertersinacustomASIC.Performancemeasurements—localstandardsandinternationalrequirementsThedevelopmentandwidespreadadoptionofadvancedpowerlinemonitoringsystemsiscomplexduetovaryinginternationalstandardsdefiningtheprecisionofenergymeasurement.Themeasurementcharacteristicsofthedeliveredenergymustcomplywithlocalstandardsorinternationalrequirements.TheEU(EuropeanUnion)standardsEN50160,IEC62053,andIEC61850dictatetheminimumaccuracyneededforamodernmultichannelADCsystemusedinpower-systemmonitoringandmetering.Powerlinemonitoringisalsoimpactedbytheincreasinglystringentaccuracyrequirementsassociatedwithreal-timepower-deliverymonitoring,faultdetectionandprotection,anddynamicloadbalancing.Asanexample,theEUstandardIEC62053Class0.2(whichisincreasinglyusedasacommonstandardworldwide)requiresmeterprecisiontobe0.2%ofnominalcurrentandvoltage.Forpower-factoraccuracymeasurement,phasematchingshouldbe0.1%orbetter.Notonlyistheminimumaccuracyspecified,butinternationalandlocalstandardsalsodictatethesamplerateneededforamodernsystemusedinpowerlinemonitoringandmetering.Thereisnowaneedforrigorousanalysisofmultiplehigh-orderharmonicsoftheACsupplyandfordetectionofhigh-speedfaultconditionssuchasinstantaneousspikesandbrownouts.Consequently,theseapplicationstypicallyrequireaccurate,simultaneousmultichannelmeasurementoverawidedynamicrangeofupto90dBwithasamplerateof16kspsorhigher.ManycountriesaroundtheglobehaveadoptedversionsoftheEUstandards,sothesestandardsserveasagoodexampleofthemeasurementrequirementswhichthesystemmustmeet.Table1summarizestheEN50160Page1of7requirements.Table1.EN50160EnergySpecificationsSupplyVoltagePhenomenonAcceptableLimitsMeasurementIntervalMonitorPeriodAcceptancePercentage(%)GridFrequency49.5Hzto50.5Hz,47Hzto52Hz10s1week95,100SlowVoltageChanges230V±10%10min1week95VoltageSagsorDips(≤1min)10to1000timesperyear(under85%ofnominal)10ms1year100ShortInterruptions(≤3min)10to100timesperyear(under1%ofnominal)10ms1year100Accidental,LongInterruptions(3min)10to50timesperyear(under1%ofnominal)10ms1year100TemporaryOvervoltage(Line-to-Ground)Mostly1.5kV10ms—100TransientOvervoltages(Line-to-Ground)Mostly6kV——100VoltageUnbalanceMostly2%,butoccasionally3%10min1week95HarmonicVoltages8%THD10min1week95Fortheharmonicvoltage,theEN50160mandatesmeasurementuptothe25th-orderharmonicof50Hz/60Hzvoltages.However,forvariousnonlinearloads,suchasinductivemotorsandswitchingpower-supplydrives,measurementsmustbedoneforuptothe127th-orderharmonicof50Hz/60Hzvoltagesupply.ItisalsoimportanttonotethatemergingstandardslikeIEC61850recommendtherecordingofpower-systemtransienteventswith256samplesperACcycleorhigher.Atypicalpower-gridmonitoringapplicationStandardthroughouttheworld,3-phasepowerisdistributedusingwhatiscalledawyeconnection.Thetermwyereferstothreevoltagesthatareoffsetinphasefromeachotherbyone-thirdofacycle(120°).Afourthwire,orneutralline,isoftenusedtoaccommodateunbalancedloads.Ifloadsoneachofthethreephasesareequal,