Implementation of a Single-Phase Electronic Watt …

1 ApplicationReportSLAA517E May 2012 RevisedAugust2015 Implementationof a single -PhaseElectronicWatt-HourMeterUsin gthe MSP430F6736(A)Bart Basile,StefanSchauer,KripasagarVenkatABS TRACTT hisapplicationreportdescribesthe implementationof a single -phaseelectronicelectricitymeterus ingthe TexasInstrumentsMSP430F673x(A) alsoincludesthe necessaryinformationwith regardto metrologysoftwareand hardwareproceduresfor this adhereto thesestepsand/ornotheedthesafetyrequirem entsat eachstepmayleadto shock,injury,and damageto the is describedin this applicationreportcan be MSP430F6736 Asourcecodealongwith the EVM430-F6736designfiles that are describedin thisapplicationreportcan be of ConnectionUsingMSP430F6736(A)..43A SimpleCapacitivePowerSupplyfor the for for Viewof the a trademarkof othertrademarksare the propertyof May 2012 RevisedAugust2015 Implementationof a single -PhaseElectronicWatt-HourMeterUsin gtheMSP430F6736(A)SubmitDocumentationFee dbackCopyright 2012 2015, Viewof the EVMWithBlocksand Viewof the Errors(for manualcorrection).

2 (1 of 5)..2624 Schematics(2 of 5)..2725 Schematics(3 of 5)..2826 Schematics(4 of 5)..2927 Schematics(5 of 5)..30 List of Tables1 HeaderNamesand JumperSettingson the F6736(A) (%) Calibratedat 230 V, 15 A, 50 MSP430F6736(A)deviceis the latestmeteringsystem-on-chip(SoC),that belongsto theMSP430F67xxfamilyof familyof devicesbelongsto the powerful16-bitMSP430F6xxxplatformand includesnew featuresand flexibilityto supportrobust1-phase,2-phase,and applicationreport,however,discussesthe implementationof a theirapplicationin energymeasurementand havethe F6736(A)has a powerful25-MHzCPUwith analogfrontendconsistsof up to three24-bit analog-to-digitalconverters(ADC)basedon a second-ordersigma-deltaarchitecturethat sigma-deltaADCs( 24) operateindependentlyand be groupedtogetherfor simultaneoussamplingof voltageand currentsonthe addition,the ADCshavean integratedgain stagethat supportsgainsup to 128 foramplificationof 32-bitx 32-bithardwaremultiplieron this chip can be usedto softwaresupportscalculationofvariouspara metersfor key parameterscalculatedduringenergymeasurem entsare: RMScurrentand voltage,activeand reactivepower,activeand reactiveenergy,powerfactor,and providedand can be MSP430F6736-basedsoftwareand a single -PhaseElectronicWatt-HourMeterUsin gtheSLAA517E May 2012 RevisedAugust2015 MSP430F6736(A)SubmitDocumentationFeedbac kCopyright 2012 2015, showstypicalconnectionsof electronicelectricitymeters(alsocalleden ergymetersor e- meters )in supportedac voltagesand associatedcurrentsare 230 V or 120 V at 50 Hz or60 Hz.

3 The labelsLINEand NEUTRAL indicatelow-voltageac comingfromthe TypicalConnectionsInsideElectronicMeters Moreinformationon the currentand voltagesensors,ADCs,and otherhardwareis providedin showsa blockdiagramof the high-levelinterfacethat is usedfor a single -phaseenergymeterapplicationusingt he F6736(A).A single -phasetwo-wirestar connectionto the mainsis connectedto eachof the currentchannels,and a simplevoltagedivideris usedto measurethe CT has an associatedburdenresistorthatmustbe connectedat all timesto protectthe choiceof the CT and the burdenresistoris donebasedon the manufacturerand currentrangerequiredfor the shuntresistorvalueis determinedby the currentrange,gain settingsof the SD24,and thepowerdissipationat the voltagedividerresistorsfor the voltagechannelare selectedtomakesurethat the mainsvoltageis divideddownto the normalinputrangesthat are validfor theMSP430 thesevalues,see theMSP430x5xxand MSP430x6xxFamilyUser'sGuide(SLAU208) and the device-specificdatasheet(SLAS731for the MSP430F6736and SLASE46for theMSP430F6736A).

4 3 SLAA517E May 2012 RevisedAugust2015 Implementationof a single -PhaseElectronicWatt-HourMeterUsin gtheMSP430F6736(A)SubmitDocumentationFee dbackCopyright 2012 2015,TexasInstrumentsIncorporatedxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxUSCIA1 UART or SPIV1-/Vref(O)USCIA0 Vref(I)USCIA2LF Crystal 32kHzXINXOUT24-bit SDAnalog to DigitalI InV InFrom utilityCTV1+I1+I1-I2+I2-N(L)L(N)RSTVSSVC CMSP430F6736(A)Application interfacesLOADV1-VREFPULSE1 PULSE2 USCIB0 UART or SPIUART or SPII2C or SPISx, 1-Phase2-WireStarConnectionUsingMSP430F6 736(A)L and N referto the line and neutralvoltages,respectively,and are interchangeableas long as the deviceis subjectto only one voltageand not bothsimultaneouslyat its othersignalsof interestare thePULSE1and usedto transmitactiveand reactiveenergypulsesusedfor accuracymeasurementand sectiondescribesthe hardwarefor the designof a working1-phaseenergymeterusingtheF6736(A ).

5 MSP430devicesare numberof low-powermodesand improvedpowerconsumptionduringactivemode whenthe CPUandotherperipheralsare low-powerfeaturesof this devicefamilyallowthe designof the powersupplyto be extremelysimpleand powersupplyallowsthe energymeterto be powereddirectlyfromthe followingsectionsdescribethe variouspowersupplyoptionsthat areavailableto a single -PhaseElectronicWatt-HourMeterUsin gtheSLAA517E May 2012 RevisedAugust2015 MSP430F6736(A)SubmitDocumentationFeedbac kCopyright 2012 2015, (RC)PowerSupplyFigure3 showsa simplecapacitorpowersupplyfor a singleoutputvoltageof V directlyfromthemainsvoltageof 110 V and 220 V and 50 Hz and 60 Hz A SimpleCapacitivePowerSupplyfor the MSP430 EnergyMeterAppropriatevaluesof resistorR20 and capacitorC28 are chosenbasedon the requiredoutputcurrentdriveof the directlyfed to a RC-basedcircuitfollowedby rectificationcircuitryto providea dc voltagefor the operationof the dc voltageis regulatedto V forfull-speedoperationof the the circuitin Figure3, the driveprovidesapproximately12 designequationsfor the powersupplyare shownin theCapacitorPowerSuppliessectionofMSP430 FamilyMixed-SignalMicrocontrollerApplica tionReports(SLAA024).

6 If thereis a needto slightlyincreasethe currentdrive(up to 20 mA),the capacitorvaluesof C28 can be drivehigherthan20 mAis required,especiallyto driveRF technology,additionaldrivecan be usedeitherwith an NPNoutputbufferor a transformerand MSP430analogfrontend that consistsof the ADCis differentialand requiresthat the inputvoltagesat the pins do not exceed 920 mV (gain= 1). To meetthis specification,the currentand voltageinputsneedto be addition,the SD24allowsa maximumnegativevoltageof -1 V,therefore,ac signalsfrommainscan be directlyinterfacedwithoutthe needfor analogfrontend usedfor voltageand currentchannels, voltagefromthe mainsis usually230 V or 110 V and needsto be broughtdownto a rangeof 1 analogfrontend for voltageconsistsof spikeprotectionvaristors(not shownin this figure)followedbya simplevoltagedividerand a RC low-passfilter that acts like an showsthe analogfrontend for the voltageinputsfor a mainsvoltageof 230 V.

7 The voltageisbroughtdownto approximately700 mV RMS,whichis 990 mV peakand fed to the positiveinput,adheringto the MSP430 common-modevoltageof zerocan be connectedto thenegativeinputof the . In addition,the has an internalreferencevoltageof V that can be usedexternallyand also as a common-modevoltageif referencedto the neutralvoltageor linevoltage,dependingon the placementof the May 2012 RevisedAugust2015 Implementationof a single -PhaseElectronicWatt-HourMeterUsin gtheMSP430F6736(A)SubmitDocumentationFee dbackCopyright 2012 2015, AnalogFrontEnd for VoltageInputsIt is importantto notethat the anti-aliasresistorson the positiveand negativesidesare different,becausethe inputimpedanceto the positiveterminalis muchhigherand,therefore,a lowervalueresistoris usedfor the this is not maintained,a relativelylargephaseshift of analogfront-endfor currentinputsis a little differentfromthe analogfrontend for the showsthe analogfrontend usedfor the currentchannelsI1 and AnalogFrontEnd for CurrentInputsResistorsR14 and R18 are the burdenresistorsthat wouldbe selectedbasedon the currentrangeusedand the turns-ratiospecificationof the CT (not requiredfor shunt).

8 The valueof the burdenresistorfor thisdesignis around13 . The anti-aliasingcircuitryconsistingof R and C followsthe the converteris a fully differentialinputwith a voltageswingof 920 mV maximumwith gainof the converterset to 1. Similarto the voltagechannels,the commonmodevoltageis selectableto eitheranalogground(GND)or internalreferenceon channelsconnectedto LSP3and a single -PhaseElectronicWatt-HourMeterUsin gtheSLAA517E May 2012 RevisedAugust2015 MSP430F6736(A)SubmitDocumentationFeedbac kCopyright 2012 2015,TexasInstrumentsIncorporatedfmfsOSR = softwarefor the implementationof 1-phasemetrologyis discussedin this first subsectiondiscussesthe set up of variousperipheralsof the ,the entiremetrologysoftwareisdescribedas two majorprocesses:foregroundprocessand primaryperipheralsusedfor this applicationare the 24-bitsigmadelta(SD24)ADC,clocksystem,ti mer,LCD,and watchdogtimer(WDT).

9 F673x(A)familyhas up to a singlephasesystemat leasttwo s are necessaryto independentlymeasureone voltageand codeaccompanyingthis applicationreportaddressesthe metrologyfor a 1-phasesystemwith limiteddiscussionto anti-tampering,however,the codesupportsthe measurementof the the SD24(fM) is derivedfromthe DCOrunningat 16 samplingfrequencyis definedas, the OSRis chosento be 256 and the modulationfrequency,fM, is chosenas 1 MHz(1048576 Hz), resultingin a samplingfrequencyof SD24sare configuredto followingare the channelsassociations: SD0P0and SD0N0 VoltageV1 SD1P0and SD1N0 CurrentI1 SD2P0and SD2N0 CurrentIN (Neutral) foregroundprocessincludesthe initialset up of the MSP430hardwareand softwareimmediatelyaftera showsthe flowchartfor this May 2012 RevisedAugust2015 Implementationof a single -PhaseElectronicWatt-HourMeterUsin gtheMSP430F6736(A)SubmitDocumentationFee dbackCopyright 2012 2015,TexasInstrumentsIncorporatedRESETHW setupClock, SD24_B, Port pins, Timer,USCI, LCDC alculate RMS values for current,voltage; Active and ReactivePowerMain Power OFF?

10 1 second of Energyaccumulated? Wait foracknowledgement fromBackground processGo to LPM0 YNYNWake-upSend Data out through SPI/UART to ForegroundProcessThe initializationroutinesinvolvesthe set up of the analogto digitalconverter,clocksystem,generalpurp oseinput/output(GPIO)port pins,timer,LCDand the USCI_A1for universalAsynchronousreceiver/transmitte r(UART) checkis madeto see if the mainpoweris OFFand the devicegoesinto ,the backgroundprocessnotifiesthe foregroundprocessthrougha statusflag everytime a frameof datais availablefor dataframeconsistsofaccumulationof energyfor 1 is equivalentto accumulationof 50 or 60 cyclesof datasamplessynchronizedto the addition,a samplecounterkeepstrackof howmanysampleshavebeenaccumulatedoverthe countcan vary as the softwaresynchronizeswith the datasamplesset consistof processedcurrent,voltage,activeand valuesare accumulatedin separate48-bitregistersto furtherprocessand obtainthe RMSand sectionbrieflydescribesthe formulasusedfor the voltage,current,and a single -PhaseElectronicWatt-HourMeterUsin gtheSLAA517E May 2012 RevisedAugust2015 MSP430F6736(A)SubmitDocumentationFeedbac kCopyright 2012 2015,TexasInstrumentsIncorporatedEPSampl e countACTACT= ( ) ( )