Implementation of a Single-Phase Electronic Watt …

1 ApplicationReportSLAA494A May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxFengHou, ,injury, ,injury, : a a May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013, energymeasurementandhavethenecessaryarch itecturetosupportit. TheMSP430 AFE2xxdeviceshavea powerful12-MHzcentralprocessingunit(CPU) (ADCs)basedonasecond-ordersigma-delta( ) ADCs(SD24) common-modevoltageofupto-1V ,it 16-bitx (RMS)currentandvoltage,activeandreactive powerandenergy,powerfactor, single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatedABCTEST REAC MAXLCDDISPLAYkWkWh20-pin20-pinWirelessDa ughterCard EMKI nterfaceVCCGNDISOLATEDac/dcPOWERSUPPLYVC CGNDSPIUSBSPISPIMSP430F6638 APPLICATIONPROCESSORUSB COMMTO PCSCLKI/OF6638 JTAGL2N2ac mainsELECTRICALISOLATIONBOUNDARYAFE JTAGGPIOVCCXT2 INXT2 OUT8 MHzHFcrystalSCLKSIMOSOMIURXD0 UTXD0 RSTVSSAFEMSP430 Analog toDigitalI1-I1+V1+V1-VREFSPIRELAYCIRCUIT RYRS 232 BRIDGEUART TO PCLOADVCCGNDI InV InCapacitivePower supplyac mainsL1N1 Optical a slavemetrologyprocessorandtheMSP430F6638 is (SPI)

2 Oruniversalasynchronousreceiver/transmit ter(UART). May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatedUTXD0V 1 - /(O )SPI(I)URXD0XT2 INXT2 OUTA nalog toDigitalI InV InFrom utilityCTV1+I1+I1-I2+I2-NLRSTVSSVCCMSP43 0 AFEA pplicationinterfaceUART or SPILOADV1-VREFPULSE1 PULSE2HF crystal(Up to12 MHZ) showsthehigh-levelinterfacefora single -phasetwo-wirestarconnectiontothem ainsis ,anda voltagedivideris (CT) determinedbythecurrentrange,gainsettings oftheSD24ontheAFE, selectedtoensurethemainsvoltageis ,seetheMSP430x2xxFamilyUser'sGuide(SLAU1 44) single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatedR1US20K 275L2N2N_APPL_APPLLNN26262222C28+ /400VV0+V0+DVCC_APP_PLV0 150 FC36C37+ NCNCL1 LINEL51 HLINE_AV1R1US20K275470n/ 400VC49R2256R / +2200 C251 TPS770335 INOUTIC334 ENFBGND2ZD1 DNP( )C26C2310 DVCC_PLDGND_AFEDGND_AFECONNECT AGND and N1 NEUTRAL1 (RC)PowerSupplyFigure3 showsa simplecapacitorpowersupplyfora directlyfromthemainsvoltageof110/220 VRMS alternatingcurrent(ac).

3 FeddirectlytoanRC-basedcircuitfollowedby rectificationcircuitrytoprovidea directcurrent(dc) Figure3, (SLAA024). If additionaldriveis required,eitheranNPNoutputbufferora transformer- ,a switching-basedpowersupplyis differentialandrequiresthattheinputvolta gesatthepinsdonotexceed 500mV(gain= 1).Tomeetthisspecification, ,theSD24allowsa maximumnegativevoltageof-1V;therefore, May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013, pFV1+V1 15 usually230V or110V andmustbebroughtdowntoa rangeof500mV(seeFigure5). Theanalogfrontendforvoltageconsistsofspi keprotectionvaristors(notshown)followedb ya showstheanalogfrontendforthevoltageinput sfora ,whichis 495mVpeak, , thatcanbeusedexternallyandalsoasa common-modevoltage,if ,becausetheinputimpedancetothepositivete rminalis muchhigherand,therefore,a lower-valueresistoris thisdifferenceis notmaintained,a single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatedAVCC_AF ECUR1+ R171K1KR18R18 GNDC1747pF47pFI1+I1 C3015nFCUR2+CUR2 +C3415nFIN theburdenresistorthatis selectedbasedonthecurrentrangeandtheturn s-ratiospecificationoftheCT(notrequiredf orshunt).

4 Theanti-aliasingcircuitryconsistingofR andC a fullydifferentialinputwitha voltageswingof ,thecommon-modevoltageis selectabletoeitheranalogground(AGND_AFE) discussedin (SD24)ADC,clocksystem,timer,andwatchdogt imer(WDT).7 SLAA494A May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatedRESETHW setupClock, SD24, Port pins,Timer,USARTC alculate RMS values forcurrent, voltage; Activeand Reactive PowerMain Power OFF?1 second of Energyaccumulated? Wait foracknowledgement fromBackground processGo to LPM0 YesNoYesNoWake-upSend Data out , single -phasesystem, (fM) is derivedfroman8-MHzexternalcrystal(ACLK). Thesamplingfrequencyis definedasfS= chosenas256,andthemodulationfrequencyfM, is chosenas1 MHz,resultingin a + + CurrentI2(Neutral) + single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporated901Re( )( )Samplecountnactpvni nPKSample count= = ( ) ( )1 Samplecountv ni nnPKActpSample count ==2( )1 SamplecountinphnIKRMSiSample count ==*2( )1 SamplecountvnphnVKRMSvSample count ==* ,Clocksystem,general-purposeinput/output (GPIO)(port)pins, checkis madeifthemainpoweris ,thebackgroundprocessnotifiestheforegrou ndprocessthrougha statusflageverytimea frameofdatais ,a ,voltage, ,current, theprevioussections,simultaneousvoltagea ndcurrentsamplesareobtainedfromthreeinde pendent convertersata 1 secondis (n)= Voltagesampleata sampleinstant n'i(n)

5 = Currentsampleata sampleinstant n'Samplecount= Numberofsamplesin 1 secondKv= ScalingfactorforvoltageKi= frame' (samplecount) (n)= Voltagesampleata sampleinstant n' shiftedby90 Kp= Scalingfactorforpower9 SLAA494A May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013, thencalculatedbasedontheactivepowervalue foreachframe,similartothewaytheenergypul sesaregeneratedin thebackgroundprocessexceptthat:EACT= PACT SamplecountForreactiveenergy,usethe90 phaseshiftapproachfortworeasons: It allowsaccuratemeasurementofthereactivepo werwithverysmallcurrents. It ,it is discussedin realizedbyprovidinganN realizedbya fractionaldelayfilter( ). triggertocollectvoltageandcurrentsamples (threevaluesin total).Thesesamplesarefurtherprocessedan daccumulatedin (onesecondworth)havebeenaccumulated,thef oregroundfunctionis triggeredtocalculatethefinalvaluesofVRMS , IRMS, power, alsowhollyresponsibleforenergyproportion alpulses, single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatedSD24 Interrupts @3906/secRead Voltages V1 Read Currents I1,and I2 Store readings and notifyforeground processPulse generation in accordanceto power accumulationCalculate frequencyCalculate power factorReturn From Interrupt1 second of energycalculated?

6 NoYesYesa. Remove residual dcb. Accumulate samples for instantaneousPowerc. Accumulate for Ifor both currents fullydifferentialinputand,therefore,noad deddcoffsetis neededtopreconditiona signal,whichis a removedindependentlyforV andIbysubtractinga long-termdctrackingfilter' synchronizedtothemainscycletoyielda : Accumulatedsquaredvaluesofvoltageandcurr entforVRMSandIRMS calculations. Accumulatedenergysamplestocalculateactiv eenergy. Accumulatedenergysampleswithcurrentand90 May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporated360360 == ooffininDelay resolutionDegOSRffsmSD16 OSRx = 32f cycles:M323240 Load SD16 PREx:SD16 PREx = 8 PreloadAppliedDelayed ConversionResultTimeConversionDelayed ,whenusedasa sensor,andtheinputcircuit' a functionofinputfrequency(fin), OSRandthesamplingfrequency(fs).Inthisapp licationforinputfrequencyof60Hz,OSRof256 andsamplingfrequencyof3906,theresolution foreverybitin thepreloadregisteris witha (maximumof255steps).

7 Becausethesamplingofthethreechannelsareg rouptriggered,a methodoftenusedis thecurrentdesignto . WhenusingCTsthatprovidea largerphaseshiftthanthismaximum, andV signalsforeachphaseareaccumulatedin , , single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatednoise corrupted samplesgood sampleslinear ,thesamplecodedoesa ,thecodesusesa ,withtwonegativesamples,a noisespikecanmakeoneofthempositiveand,th erefore,makethenegativeandpositivepairlo oksasif therewerea a stableandaccuratefrequencymeasurementtha tis ,theenergyconsumedis normallymeasuredin fractionofkilowatt-hour(kWh) , is a ,aslongasthejitteris averagedout,it cangivea (calculatedbytheforegroundprocess)is equivalenttoconvertingit threshold,a pulseis stored,andnewenergyamountis addedtoit in stablevalue, a constant,forexample,it canbein , ,in thisapplication,thenumberofpulsesgenerat edperkWhis thiscaseis 1 May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013,TexasInstrumentsIncorporatedSD interrupts @3906 HzEnergyAccumulator+=Average PowerEnergy Accumulator >1 KWh threshold?

8 Energy Accumulator-=1 KWh threshold?Generate 1pulseProceed to in kWhthresholdis definedas:1 kWhthreshold= 1 / 1 kW (numberofinterrupts/sec) (numberofsecondsin 1 hour)= 100000 3906 3600= includesmacrodefinitionsthatareuseddurin gthenormaloperationofthemeter. MAINS_FREQUENCY_SUPPORT:Themacroconfigur esthemetertomeasurethefrequencyofthemain s. MAINS_NOMINAL_FREQUENCY:Themacrodefinest hedefaultmainsfrequency,whichis a startingpointfordynamic-phasecorrectionf ornonlinearCTsorothersensorsforwhichthep hasechangeswiththecurrent. TOTAL_ENERGY_PULSES_PER_KW_ ,it is nota standard,butit practicallimitsetonthisnumberduetotheref erencemeter'sabilitytoacceptfastpulses(d uetolargecurrents).14 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013, ENERGY_PULSE_ measuredin ADCsamples(thatis,incrementsevery1/3906s ).Themaximumallowedis255,givinga ,while163givesa is recommendedthatthisvaluebechangedtoa smallernumbersuchas80if overlapis seenatthepulseoutputs.

9 NEUTRAL_MONITOR_ usedforthispurpose. VRMS_SUPPORT:Thismacroconfiguresthemeter tocalculateVRMS fromthevoltagesamples. IRMS_SUPPORT:Thismacroconfiguresthemeter tocalculateIRMS fromthecurrentsamples. REACTIVE_POWER_SUPPORT:Thismacroconfigur esthemetertocalculatethereactivepowerfro mthevoltageandcurrentsamples. REACTIVE_POWER_BY_QUADRATURE_SUPPORT:Thi smacroconfiguresthemetertocalculatethere activepowerfromthedelayedvoltagesamplesb y90 andcurrentsamplesinsteadofusingthepowert rianglemethod. APPARENT_POWER_SUPPORT:Thismacroconfigur esthemetertocalculatetheapparentpower. POWER_FACTOR_ frequency-independentmethod,basedonthera tioofscalardotproducts,is used. CURRENT_LIVE_GAIN:Thismacrodefinesthegai noftheSD24'sinternalprogrammablegainampl ifier(PGA) is setto1. CURRENT_NEUTRAL_GAIN:Thismacrodefinesthe gainoftheSD24' is setto16. VOLTAGE_GAIN:Thismacrodefinesthegainofth eSD24' is setto1. DEFAULT_V_RMS_SCALE_FACTOR_ valuethatis in anacceptablerangeandis finetunedduringcalibration.

10 DEFAULT_I_RMS_SCALE_FACTOR_ valuethatis in anacceptablerangeandis finetunedduringcalibration. DEFAULT_P_SCALE_FACTOR_A_ canbesettoa valuethatis in anacceptablerangeandis finetunedduringcalibration. DEFAULT_I_RMS_SCALE_FACTOR_ canbesettoa valuethatis in anacceptablerangeandis May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013, (EVM) ,metrologysoftware,anda PCgraphicaluserinterface(GUI),whichis single -PhaseElectronicWatt-HourMeterUsin gtheSLAA494A May2011 RevisedMay2013 MSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013, : L andN ac50/60Hz. CUR1+ ,makesurethatthevoltagesacrossCUR1+andCU R1-donotexceed500mV. CUR2+ ,makesurethatthevoltagesacrossCUR2+ May2011 RevisedMay2013 Implementationofa single -PhaseElectronicWatt-HourMeterUsin gtheMSP430 AFE2xxSubmitDocumentationFeedbackCopyrig ht 2011 2013, ,mainsvoltage, [1-2]NojumperMainssupplyNojumperJumperon [1-2]ExternalpowerNojumperJumperon[1-2]I f JTAG debuggingis necessarywithexternalpoweris ON,thejumperon[2-3]onJTG_PWR1mustbeplace din ,thePWR1headercanalsobetreatedasa currentconsumptionheaderbyplacinganammet eracrossit.