switching monitoring high voltage dc power supplies up to … · 2018-03-20 · within a data...
TRANSCRIPT
M140,EN
Switching&MonitoringHighVoltage
DCPowerSuppliesupto1000V
ByPinkeshSachdevProductMarketingEngineer,MixedSignalProducts
LinearTechnologyCorp. IntroductionDCpowersuppliesinthehundredsofvoltsarenotasuncommonasonemightthink.AnapplicationthatmayfirstcometomindiselectricvehicleswhereLi-Ionbatterystackvoltagesrangeupto400V.Butsomelesserknownhighvoltageapplicationsareinmodernfighteraircraft,suchastheF-22RaptorandtheF-35LightningII,whichareprimarilypoweredfrom270VDCforfasterandpreciseperformance.Largesolararrayscanoutput600Vorhigher,whilerectifyingACvoltagesinindustrialmotordrivesyieldDCvoltagesrangingfrom170Vto680V.Andformanyyears,therehasbeenresearchanddevelopmenttomovepowerdistributionwithinadatacenterfromACtohighvoltageDC(380Vor±190V),loweringpowerconversionsteps,facilityfootprintandoperationalcostswhileeasingintegrationwithrenewableenergysuchassolar.Distributingpowerathighervoltageslowerscurrentlevels,reducingresistivelosses(I2•R),whichcanbeusedtoreducecablingweight.Allofthesehighvoltagesuppliesneedtobeswitchedonoroffandsoft-startedintoloads.Forenergymonitoringandoptimization,itisessentialtodigitallymonitorthevoltageandcurrentflowingonthesehighvoltagebuses.Anycircuitcontrollingthesesuppliesneedstobegalvanicallyisolatedforoperatorsafetyandtoprotectthelowvoltageelectronicsfromthedangerouslyhighvoltage.MethodstoControlInrushCurrent&MonitorPowerWhendesigninghighvoltagesupplies,animportantgoalistosafelycontrolthestartupinrushcurrentintothecapacitiveload,e.g.,theDCbuscapacitorsfollowingatypicalbridgerectifier.Asimplemethodtolowerinrushcurrentisbyusingnegativetemperaturecoefficient(NTC)thermistors,alsoknownasinrushcurrentlimiters(ICL,Figure1a).Thesethermistorsstartwithahighresistance(e.g.,fewohms)atroomtemperaturebeforethesupplyorloadisturnedon;thehighresistancelimitstheinrushcurrentatturn-on.Ascurrentflows,thethermistorheatsupanditsresistancedropsbyonetotwoordersofmagnitude(by10x–100xtobelowanohm).Thesethermistorscostanywherefrom$0.13to$7each,dependingoncurrentandresistanceratings.Whilesimpletouse,oneproblemisthataquickpowercycling(on-off-on)maynotlimitinrushonthesecondpower-upifthethermistordidn’thavesufficienttimetocooldowntothehighresistancestate.NTCthermistorssufferfromwidetolerances(±25%),andsincetheinrushcurrentistiedtothesteadystatecurrentthroughtheresistancedropratio,theinrushcannotbeflexiblyadjustedtoarbitrarilylowlevels.ICLsfindapplicationsinvacuumcleaners,fluorescentlamps,andswitched-modepowersupplies,reducinginrushtothebridgerectifier’sDCbuscapacitors.
ToovercometheNTCthermistordownsideofnoinrushlimitingonaquickrestart,ashortingrelayisusedinparallelwiththeresistor.Thisisknownasastepstartrelay(Figure1b).Atturn-on,theparallelrelayisopenandinrushislimitedbytheresistor.Atimerisalsostarted;whenitexpires,therelayisshortedacrosstheresistor.Loadcurrentnowflowsthroughtherelay.Onaquickrestart,thestep-startrelayisabletoprovideinrushlimiting.Thistechniquerequirestheadditionofashortingrelayandatimertocontrolitsturnon.Theincreasedcomplexityraisesthesolutioncostintothe$20–$30range.
Otherinrushcurrentcontroltechniquesincludezerocrossingtriacs,activepowerfactorcontrolcircuits,andinductiveinputfilteringwithdamping.Mostofthesearecomplicated,bulky,expensive,andapplicableonlytoACinputs.Onemethodforisolatedcurrentmonitoringisbyusinganisolationamplifieracrossacurrentsenseresistorandadifferential-to-singleendedconversionamplifierfeedinganADC.Anothermethodistouseanisolateddelta-sigma(ΔΣ)modulatorwithanexternaldigitalfilter.Asseen,controlling,protecting,andmonitoringhighvoltageDCsuppliesrequirescobblingmanycomponentstogetherandmakingthemworksafelyandseamlessly.Thisisnotatrivialtask.Thesediscretesolutionsarelarge,component-intensive,expensive,andlacksafetycertifications.Anintegratedandcertifiedsolutionisneededtoshortendesigntimeandcertificationeffortfrommanymonthsintoafewweeks. IntegratedSolutionforHighVoltagePowerControl&TelemetryTheLTM9100µModule®(micromodule)ICisacompactall-in-onesolutionforcontrolling,protecting,andmonitoringhighvoltagepowersuppliesupto1000VDC(Figure2a).A5kVRMSisolationbarrierseparatesthelogicanddigitalinterfacefromtheswitchcontrollerdrivinganexternalN-channelMOSFETorIGBTswitch.Theisolationisneededforcontrolcircuitprotection,operatorsafety,andbreakinggroundpaths.Theloadissoft-started(Figure2b)andthesupplyisprotectedfromoverloadwithacurrent-limitedcircuitbreaker.Isolated10-bitADCmeasurementsofloadcurrentandtwovoltageinputsareaccessedviatheI2C/SMBusinterface,enablingpower,energyandthermalmonitoringofthehighvoltagebus.
TheLTM9100utilizesLinearTechnology’sisolatorμModuletechnology(Figure3)totranslatesignalsandpoweracrossanisolationbarrier.SignalsareencodedintopulsesandpassedacrosstheisolationboundaryusingcorelesstransformersformedintheµModulesubstrate,resultinginanextremelyrobustbidirectionalcommunicationscheme.Uninterruptedcommunicationisguaranteedforcommonmodetransientsof50kV/µs.TheisolatedsideispoweredbyafullyintegratedDC/DCconverter,includingthetransformer,eliminatingtheneedforexternalcomponents.Toguaranteearobustisolationbarrier,eachLTM9100controllerisproduction-testedto6kVRMS.TheLTM9100willberecognizedbytheUL1577standard,savingmonthsofcertificationtimefortheendequipmentmanufacturer.Highdistancethrough-insulationtranslatestoahigh±20kVESDlevelacrossthebarrier.TheμModulepackageintegratesseveralcomponentsandtechnologiestodeliveracost-effective,advancedsolutionthatminimizesboardspaceandimproveselectricalandthermalperformance.
Duetoitsisolatednature,theLTM9100iseasilyconfiguredforhighside,lowside(groundreturn)andfloatingapplications(Figure4).TheLTM9100isversatileenoughtocontrol
inrushcurrentnotjustinhot-swappablecards,butalsoinACtransformers,motordrives,andinductiveloads.Adjustableundervoltageandovervoltagelockoutthresholdsensurethattheloadoperatesonlywhentheinputsupplyisinitsvalidrange.The22mmx9mmx5.16mmBGApackageprovides14.6mmofcreepagedistancebetweenthelogicsideandtheisolatedside. ConclusionTraditionally,highvoltageDCsuppliesarefoundinindustrialenvironments,butotherelectronicsystemsarealsomovingtowardshighervoltagestolowercostsandraisetheefficiencyofpowerdistribution,especiallyinpower-hungrysystems.Thesesuppliesneedasimplewaytocontrolinrushcurrent,protectthemselvesandtomonitortheirusage.Thefirst-of-its-kindLTM9100deliversthissimpleandcompactsolution,beatingdiscreteandrelaybasedcircuitsbyprovidingacertifiedready-to-gosolution,savingboardareaandmultiplemonthsofdesigntimeandcertificationeffort.Alltheneededfunctionality,includingdigitaltelemetryandisolatedpower,iswrappedinacompact,surfacemount,andlow-profileBGApackage. FIGURES
Figure1.InrushControlLimiters.(a)NegativeTemperatureCoefficient(NTC)Thermistor(b)StepStartRelay
Figure2.(a)LTM9100AnysideTMHighVoltageIsolatedSwitchControllerwithTelemetry(b)LTM9100soft-starting,a270VLoadwithControlled200mAInrushCurrent