Current Sensing Techniques- A Review

354IEEESENSORSJOURNAL,VOL.9,NO.4,APRIL2009CurrentSensingTechniques:AReviewSilvioZiegler,RobertC.Woodward,HerbertHo-ChingIu,SeniorMember,IEEE,andLawrenceJ.Borle,Member,IEEEAbstract—Thispaperprovidesathoroughreviewofstate-of-the-artcurrentsensingtechniques.Itcataloguesthecurrentsensorsaccordingtotheunderlyingphysicalprincipleinordertopointouttheirstrengthsandweaknesses.NewcurrentsensingprinciplesbasedoneitherestablishedtechniquessuchasHall-effectsensorsandfluxgateprinciplesoremergingtechnologiessuchasmagnetoresistanceeffectandfiber-opticaltechniquesprovideattractivealternativesforcurrentsensing,althoughgenerallyatahigherpricethantraditionaltechniqueslikeshuntresistors.IndexTerms—Currentmeasurement,currenttransformers,fluxgates,Hall-effectsensors,magnetoresistance,shuntresistor.I.INTRODUCTIONINFORMATIONregardingcurrentflowisrequiredinawiderangeofelectricalandelectronicsapplications.Eachappli-cationhasdifferentperformancerequirementsintermsofcost,isolation,precision,bandwidth,measurementrange,orsizeandmanydifferentcurrentmeasurementmethodshavebeende-velopedtosatisfythesedemands.Today,currentinformationincreasinglyneedstobeavailableindigitalformfordigitalcontrolormonitoringpurposes.Thisrequirestheoutputsignalofaparticularcurrentsensingtechniquetobeacquiredbyananalog-to-digitalconverter.Asanexample,shuntresistorshavebeenusedextensivelyinpowerelectronicsduetotheirlowcost,smallsize,andrelativesimplicity,whileprovidingreasonableaccuracy.Toachievehigherintegration,higherefficiencyandenablemoresophisticatedcontroltechniques,theanalogcontrolloopsareincreasinglyreplacedbydigitalcontrolloops.Accordingly,thecurrentinformationneedstobedigitalized.Thesmallvoltagedropacrossashuntresistorneedsamplification,whichaltersthebandwidth,andincreasesthedevicesizeandcost.Powerconverters,moreover,havereachedapowerdensitylevel,wherethepowerlossesinsideshuntresistorstarttobe-cometroublesome.Therefore,powerelectronicsengineersareseekingalternativesforshuntresistorswithsimilaraccuracybutlowerpowerlosses,andwithanoutputvoltagethatcanbedirectlysampledbyananalog-to-digitalconverter.ManuscriptreceivedSeptember20,2008;acceptedOctober27,2008.CurrentversionpublishedFebruary27,2009.ThisworkwassupportedinpartbythecompanyPower-One,Inc.TheassociateeditorcoordinatingthereviewofthispaperandapprovingitforpublicationwasDr.KailashThakur.S.Ziegler,H.H.C.Iu,andL.J.BorlearewiththeSchoolofElectrical,ElectronicandComputerEngineering,UniversityofWesternAustralia,Crawley,WA6009,Australia(e-mail:[e-mail];[e-mail];[e-mail]).R.C.WoodwardiswiththeSchoolofPhysics,UniversityofWesternAus-tralia,Crawley,WA6009,Australia(e-mail:[e-mail]).Colorversionsofoneormoreofthefiguresinthispaperareavailableonlineatfiedthecurrentsensingtechniquesbasedupontheunderlyingfunda-mentalphysicalprinciple.Theseprinciplesarethefollowing.1)Ohm’slawofresistance.2)Faraday’slawofinduction.3)Magneticfieldsensors.4)Faradayeffect.Inaddition,wewilldiscussknownsensingconfiguration,suchasopen-loop,closed-loop,withparticularreferencetomagneticfieldsensors,andtheuseofcombinationsofsensorsinordertomeetmoredemandingperformancerequirements.II.CURRENTSENSORSBASEDUPONOHM’SLAWOFRESISTANCEOhm’slawofresistanceisbasicallyasimplificationoftheLorentzlawthatstates(1)isthecurrentdensity,theelectricfield,thechargeve-locity,themagneticfluxdensityactingontothecharge,andthematerialconductivity.Inmostcases,thevelocityofthemovingchargesissufficientlysmallthatthesecondtermcanbeneglected(2)ThisequationisknownasOhm’slawofresistanceandstatesthatthevoltagedropacrossaresistorisproportionaltotheflowingcurrent.Thissimplerelationshipcanbeexploitedtosensecurrents.Thesecurrentsensorsoftenprovidetheadvan-tageoflowercostscomparedwithothersensingtechniques,andhavethereputationofbeingreliableduetotheirsimpleworkingprinciple.A.ShuntResistorAcommonapproachduetoitssimplicityistheuseofashuntresistorforcurrentsensing.Thevoltagedropacrosstheshuntresistorisusedasaproportionalmeasureofthecurrentflow.Itcanbeusedtosensebothalternatingcurrents(AC)anddi-rectcurrents(DC).Theshuntresistorisintroducedintothecur-rentconductingpath,andcan,therefore,generateasubstantialamountofpowerloss.ThepowerlosscanbecalculatedviaOhm’slawandincreaseswiththesquareofthecurrent.Thispowerlossmayrestricttheuseofshuntresistorsinhighcurrentapplications.1)High-PerformanceCoaxialShunt:Shuntresistorshavebeenusedextensivelytomeasuretransientcurrentpulseswithfastrise-timesandhighamplitudes.Insuchapplications,the1530-437X/$25.00©2009IEEEAuthorizedlicenseduselimitedto:NortheasternUniversity.DownloadedonNovember30,2009at20:36fromIEEEXplore.Restrictionsapply.ZIEGLERetal.:CURRENTSENSINGTECHNIQUES:AREVIEW355Fig.1.Equivalentcircuitdiagramforashuntresistor.Fig.2.Impedancemeasur