PLCBasedMonitoringControlSystemforInductionMotorPLC.docx

PLCBasedMonitoringControlSystemforInductionMotorPLC.docx

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PLCBasedMonitoringControlSystemforInductionMotorPLC

DesignandImplementationofPLC-BasedMonitoringControlSystemforInductionMotor

Abstract：

Theimplementationofamonitoringandcontrolsystemfortheinductionmotorbasedonprogrammablelogiccontroller（PLC）technologyisdescribed.Also,theimplementationofthehardwareandsoftwareforspeedcontrolandprotectionwiththeresultsobtainedfromtestsoninductionmotorperformanceisprovided.ThePLCcorrelatestheoperationalparameterstothespeedrequestedbytheuserandmonitorsthesystemduringnormaloperationandundertripconditions.TestsoftheinductionmotorsystemdrivenbyinverterandcontrolledbyPLCproveahigheraccuracyinspeedregulationascomparedtoaconventionalcontrolsystem.TheefficiencyofPLCcontrolisincreasedathighspeedsupto95%ofthesynchronousspeed.Thus,PLCprovesthemselvesasaveryversatileandeffectivetoolinindustrialcontrolofelectricdrives.

Keywords：

Computer-controlledsystems,computerizedmonitoring,electricdrives,inductionmotors,motioncontrol,programmablelogiccontrollers（PLCs）,variable-frequencydrives,voltagecontrol.

I.INTRODUCTION

Sincetechnologyformotioncontrolofelectricdrivesbecameavailable,theuseofprogrammablelogiccontrollers（PLCs）withpowerelectronicsinelectricmachinesapplicationshasbeenintroducedinthemanufacturingautomation[1],[2].Thisuseoffersadvantagessuchaslowervoltagedropwhenturnedonandtheabilitytocontrolmotorsandotherequipmentwithavirtuallyunitypowerfactor[3].ManyfactoriesusePLCsinautomationprocessestodiminishproductioncostandtoincreasequalityandreliability[4]–[9].Otherapplicationsincludemachinetoolswithimprovedprecisioncomputerizednumericalcontrol（CNC）duetotheuseofPLCs[10].Toobtainaccurateindustrialelectricdrivesystems,itisnecessarytousePLCsinterfacedwithpowerconverters,personalcomputers,andotherelectricequipment[11]–[13].Nevertheless,thismakestheequipmentmoresophisticated,complex,andexpensive[14],[15].

FewpaperswerepublishedconcerningdcmachinescontrolledbyPLCs.Theyreportboththeimplementationofthefuzzymethodforspeedcontrolofadcmotor/generatorsetusingaPLCtochangethearmaturevoltage[16],andtheincorporationofanadaptivecontrollerbasedontheself-tuningregulatortechnologyintoanexistingindustrialPLC[17].Also,othertypesofmachineswereinterfacedwithPLCs.Thereby,anindustrialPLCwasusedforcontrollingsteppermotorsinafive-axisrotorposition,directionandspeed,reducingthenumberofcircuitcomponents,loweringthecost,andenhancingreliability[18].Forswitchedreluctancemotorsasapossiblealternativetoadjustablespeedacanddcdrives,asinglechiplogiccontrollerforcontrollingtorqueandspeedusesaPLCtoimplementthedigitallogiccoupledwithapowercontroller[19].OtherreportedapplicationconcernsalinearinductionmotorforpassengerelevatorswithaPLCachievingthecontrolofthedrivesystemandthedataacquisition[20].Tomonitorpowerqualityandidentifythedisturbancesthatdisruptproductionofanelectricplant,twoPLCswereusedtodeterminethesensitivityoftheequipment[21].

OnlyfewpaperswerepublishedinthefieldofinductionmotorswithPLCs.Apowerfactorcontrollerforathree-phaseinductionmotorutilizesPLCtoimprovethepowerfactorandtokeepitsvoltagetofrequencyratioconstantunderthewholecontrolconditions[3].Thevectorcontrolintegratedcircuitusesacomplexprogrammablelogicdevice（CPLD）andintegerarithmeticforthevoltageorcurrentregulationofthree-phasepulse-widthmodulation（PWM）inverters[22].

Manyapplicationsofinductionmotorsrequirebesidesthemotorcontrolfunctionality,thehandlingofseveralspecificanaloganddigitalI/Osignals,homesignals,tripsignals,on/off/reversecommands.Insuchcases,acontrolunitinvolvingaPLCmustbeaddedtothesystemstructure.ThispaperpresentsaPLC-basedmonitoringandcontrolsystemforathree-phaseinductionmotor.Itdescribesthedesignandimplementationoftheconfiguredhardwareandsoftware.Thetestresultsobtainedoninductionmotorperformanceshowimprovedefficiencyandincreasedaccuracyinvariable-loadconstant-speed-controlledoperation.Thus,thePLCcorrelatesandcontrolstheoperationalparameterstothespeedsetpointrequestedbytheuserandmonitorstheinductionmotorsystemduringnormaloperationandundertripconditions.

II.PLCASSYSTEMCONTROLLER

APLCisamicroprocessor-basedcontrolsystem,designedforautomationprocessesinindustrialenvironments.Itusesaprogrammablememoryfortheinternalstorageofuser-orientatedinstructionsforimplementingspecificfunctionssuchasarithmetic,counting,logic,sequencing,andtiming[23],[24].APLCcanbeprogrammedtosense,activate,andcontrolindustrialequipmentand,therefore,incorporatesanumberofI/Opoints,whichallowelectricalsignalstobeinterfaced.InputdevicesandoutputdevicesoftheprocessareconnectedtothePLCandthecontrolprogramisenteredintothePLCmemory（Fig.1）.

Fig.1.ControlactionofaPLC.

Inourapplication,itcontrolsthroughanaloganddigitalinputsandoutputsthevaryingload-constantspeedoperationofaninductionmotor.Also,thePLCcontinuouslymonitorstheinputsandactivatestheoutputsaccordingtothecontrolprogram.ThisPLCsystemisofmodulartypecomposedofspecifichardwarebuildingblocks（modules）,whichplugdirectlyintoaproprietarybus:

acentralprocessorunit（CPU）,apowersupplyunit,input-outputmodulesI/O,andaprogramterminal.Suchamodularapproachhastheadvantagethattheinitialconfigurationcanbeexpandedforotherfutureapplicationssuchasmultimachinesystemsorcomputerlinking.

III.CONTROLSYSTEMOFINDUCTIONMOTOR

InFig.2,theblockdiagramoftheexperimentalsystemisillustrated.Thefollowingconfigurationscanbeobtainedfromthissetup.

a）Aclosed-loopcontrolsystemforconstantspeedoperation,configuredwithspeedfeedbackandloadcurrentfeedback.Theinductionmotordrivesavariableload,isfedbyaninverter,andthePLCcontrolstheinverterV/foutput.

b）Anopen-loopcontrolsystemforvariablespeedoperation.TheinductionmotordrivesavariableloadandisfedbyaninverterinconstantV/fcontrolmode.

c）Thestandardvariablespeedoperation.Theinductionmotordrivesavariableloadandisfedbyaconstantvoltage-constantfrequencystandardthree-phasesupply

Theopen-loopconfigurationb）canbeobtainedfromtheclosed-loopconfigurationa）byremovingthespeedandloadfeedback.Ontheotherhand,operationc）resultsiftheentirecontrolsystemisbypassed.

IV.HARDWAREDESCRIPTION

Thecontrolsystemisimplementedandtestedforawoundrotorinductionmotor,havingthetechnicalspecificationsgiveninTableI.Theinductionmotordrivesadcgenerator,whichsuppliesavariableRload.Thethree-phasepowersupplyisconnectedtoathree-phasemainswitchandthentoathree-phasethermaloverloadrelay,whichprovidesprotectionagainstcur-rentoverloads.Therelayoutputisconnectedtotherectifier,whichrectifiesthethree-phasevoltageandgivesadcinputtotheinsulatedgatebipolartransistor（IGBT）inverter.Itstechnicalspecifications[25]aresummarizedinTableII.TheIGBTinverterconvertsthedcvoltageinputtothree-phasevoltageoutput,whichissuppliedtothestatoroftheinductionmotor.Ontheotherhand,theinverterisinterfacedtothePLC-basedcontroller.

Fig.2Electricaldiagramofexperimentalsystem.

TABLEIINDUCTIONMOTORTECHNICALSPECIFICATIONS

TABLEIIINVERTERTECHNICALSPECIFICATIONS

ThiscontrollerisimplementedonaPLCmodularsystem[5],[26]–[28].ThePLCarchitecturereferstoitsinternalhardwareandsoftware.Asamicroprocessor-basedsystem,thePLCsystemhardwareisdesignedandbuiltupwiththefollowingmodules[29]–[37]:

·centralprocessorunit（CPU）

·discreteoutputmodule（DOM）

·discreteinputmodule（DIM）

·analogoutputsmodule（AOM）

·analoginputsmodule（AIM）

·powersupply.

OtherdetailsofthePLCconfigurationareshowninTablesIIIandIV.

Aspeedsensorisusedforthespeedfeedback,acurrentsensorisusedfortheloadcurrentfeedback,andasecondcurrentsensorisconnectedtothestatorcircuits[32].Thus,thetwofeedbackloopsoftheclosed-loopsystemaresetupbyusingtheloadcurrentsensor,thespeedsensor,andtheAIM.

Atachogenerator（permanentmagnetdcmotor）isusedforspeedsensing.Theinductionmachinedrivesitsshaftmechanicallyandanoutputvoltageisproduced,themagnitudeofwhichisproportionaltothespeedofrotation.Polaritydependsonthedirectionofrotation.ThevoltagesignalfromthetachogeneratormustmatchthespecifiedvoltagerangeoftheAIM（0–5Vdcand200-

internalresistance）.OtherPLCexternalcontrolcircuitsaredesignedusingalow-voltagesupplyof24Vdc.

V.SOFTWAREDESCRIPTION

PLC’sprogrammingisbasedonthelogicdemandsofinputdevicesandtheprogramsimplementedarepredominantlylogicalratherthannumericalcomputationalalgorithms.Mostoftheprogrammedoperationsworkonastraightforwardtwo-state“onoroff”basisandthesealternatepossibilitiescorrespondto“trueorfalse”（logicalform）and“1or0”（binaryform）,respectively.Thus,PLCsofferaflexibleprogrammablealternativetoelectricalcircuitrelay-basedcontrolsystemsbuiltusinganalogdevices.

Theprogrammingmethodusedistheladderdiagrammethod.ThePLCsystemprovidesadesignenvironmentintheformofsoftwaretoolsrunningonahostcomputerterminalwhichallowsladderdiagramstobedevelop