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UnderstandingtheoperationalprinciplesofthesesectionsisessentialforgraspingthefunctionalityofaVFDComponentsofVFDAVFDisapowerconverter thatuseselectroniccircuitstoconvertafixedfrequencyandfixedvoltageintoavariablefrequencyandvariablevoltage.Avariable-frequencydrive(VFD)isa systemforcontrollingtherotationalspeedofanalternatingcurrent(AC)electricmotorbycontrollingthefrequencyoftheelectricalpowersuppliedtothemotor WhenstartinganHVACfanmotorinaVFDsystem,theVFDinitiallyappliesalowfrequencyandvoltage,avoidingthehighinrushcurrentandtorqueassociated withadirectstartABSTRACTAlsocoveredareissuesrelatedtoVFDs,somesolutionstoVFDissues,andhowVFDscanbothaffectandbeimpactedbythe powerqualityofthedistributionsystemVFDOPERATIONUnderstandingthebasicprinciplesbehindVFDoperationrequiresunderstandingthethreebasic sectionsoftheVFD:therectifier,dcbus,andinverterACMotorSpeedThespeedofanACinductionmotordependsupontwofactors:Thenumberofmotor polesAVFDisanelectroniccontroldevicethatallowseficientcontroloffansandmotors,suchasthoseinanHVACsystem,byvaryingthefrequencyappliedto themotorINTRODUCTION.Variablefrequencydrive(VFD)usagehasincreaseddramaticallyinHVACapplications.AVariableFrequencyDrive(VFD) operatesonfourfundamentalcomponents:therectifier,dcbus,inverterandcontrolsystemAvariable-frequencydrive(VFD)isasystemforcontrollingthe rotationalspeedofanalternatingcurrent(AC)electricmotorbycontrollingthefrequencyoftheelectricalVFDFundamentalsThispapercoverswhatavariable frequencydrive(VFD)is,thedifferenttypesofVFDs,theirfunctions,andtheirbenefitsThevoltageonanalternatingcurrent(ac)powersupplyrisesandfallsin thepatternofasinewave(seeFigure1)ItevenenablesamotortorunaboveitsratedspeedbyincreasingthefrequencyVFDsinanHVACSystemTheVFDs arenowcommonlyappliedtoairhandlers,pumps,TechnicalnoteIthastwomainimportantfunctionslikeasoneisspeedcontrollingandsecondissmoothstart andstopThepaperpresentstheworkingprincipleofVFD,itsperformanceandtheuseofPulseWidthModulation(PWM)inthethreephaseinvertertocontrol ormaintaintheratioofWorkingPrincipleofVariableFrequencyDrive(VFD)PDFPowerInverterRectifierOthernamesforaVFDarevariablespeeddrive, adjustablespeeddrive,adjustablefrequencydrive,ACdrive,microdrive,andinverterPDFItisimportanttoknowtheworkingofVFDsorVariablefrequency drive(VFDs),astheyareextensivelyusedintheACmotor-drivenapplications,Find,readandcitealltheVFDConstructionandWorkingPrincipleWhenthe voltageispositiveVariableFrequencyDrivesVariableFrequencyDriveFundamentalsWorkingPrincipleofVariableFrequencyDriveFreedownloadasWord Docdoc/docx),AVariableFrequencyDrive(VFD)isatypeofmotorcontrollerthatdrivesanelectricmotorbyvaryingthefrequencyandvoltagesuppliedto theelectricmotorWhatisAVFD?Youcandividetheworldofelectronicmotordrivesintotwocategories:ACandDCAmotordrivecontrolsthespeed, torque,directionandVFDWorkingprinciple:VFDisanelectricalfrequencycontroldevice.VFDsareanexcellentwaytoincreasetheeficiencyofacommercial buildingHVACsystem