EC FANS ANNEX - Nicotra Gebhardt
Transcript of EC FANS ANNEX - Nicotra Gebhardt
Rev. 0 - 11/11/2020
EC FANSANNEX
Regal Beloit Italy S.p.A.
Via Modena, 1824040 Ciserano (BG) ITALYPhone +39 035 873 111Fax +39 035 884 319www.regalbeloit.com
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
2/16
INDEXINDEX
1. ANALOG SIGNAL CONSIDERATIONS ......................................................................................................................................3
1.1 Voltage and speed ..............................................................................................................................................................3
1.2 Voltage signal rescaling ......................................................................................................................................................3
1.3Potentiometersetting ........................................................................................................................................................6
2. SENSORLESS CONSTANT PRESSURE ......................................................................................................................................7
2.1Considerations ....................................................................................................................................................................8
2.2 Conclusion ..........................................................................................................................................................................8
3. SENSORLESS CONSTANT AIRFLOW .......................................................................................................................................9
4. MASTER & SLAVE CONSIDERATIONS ...................................................................................................................................10
4.1Characteristicoftwoforwardcurvedfansinparallelatsamespeed ..............................................................................11
5. PID TUNING PROCEDURE .....................................................................................................................................................12
6. REPLACEMENT OF A FORWARD CURVED FAN EQUIPPED WITH AN ACIM MOTOR WITH A DDMP FAN ................................13
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
3/16
1. ANALOG SIGNAL CONSIDERATIONS
1.1 Voltage and speed
1.2 Voltage signal rescaling
EachfanperformanceisdefinedandlimitedbyitsownSafeOperatingArea.
TheSpeedislimitedbythefanimpellerThePowerislimitedbythefandriver.TheCurrentislimitedbythefanmotor.
Themotorcurrent,theabsorbedpowerandthedrivertemperaturerepresenttheprocess,whilethespeedrepresentstheset-pointofthesystem.Therefore,thedrivercontrolloopsreducethespeedwheneveraprocessvariableexceedsitsownlimit.
ThisparagraphshowsthewaytofindthevoltageVIN required to achieve the Speed-DesiredusingthediagramSignal/Speedoffigureaside.
Inthefollowingfigure,theperformanceofaDDMP7/7Tighthasbeenextended(redcurves)supposingtohavenolimitationofpower,currentandheating.
Pict. 2
Pict. 1
Pict. 3
Pict. 4
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
4/16
Eachfanisconfiguredbydefaultatitsownmaxpossiblevalues(FanSpeed,MotorCurrentandAbsorbedPower).Forexample,themaxspeedoftheDDMP7/7Tightis3000rpmrepresentedbytheperformanceat9.5Voffigure19(lightgreen).Whiledarkgreenlinerepresentstheperformanceat5Vthatcorrespondstoaspeedof1700rpmTheblueparabolarepresentsaworkingpointwherethefanisinacurrentlimitation.Therefore, the fanperformance is the same inbothcasesof9.5Vand5VForthisreason,reducingthevoltagesignalfrom9.5Vto5Vatthatworkingpointdoesn’tchangethefanspeed.ThissituationoccursalsowhenthefanisconfiguredinModbusmode,evenifthemaxspeedisset,therealfanspeedwillbe1700rpm.
Thissituationcouldcausediscomfortwhenapotentiometerisused,thelossofsignaldynamicsistranslatedintonofanreactionwhenthepotentiometerisrotated.
Toavoidthisproblemisenoughtorescalethemaxspeedofthefan.TheprocedureissimpleandrequirestheModbusconnection:• Installthefaninsidetheunitatthesameconditionofthefinalapplication.• Startthefanatitsmaxspeed.• ReadtherealspeedfromtheInputRegistersn°3.• SetthemaxfanspeedbychangingHoldingRegistern°2atthepreviouslyreadvalue.
Pict. 5
Pict. 6
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
5/16
Thesituationafterrescalingthespeedisshowninthefollowingfigure:
Therescalingobviouslyaffectsthebehaviorincaseofchangeofthefanload(forexampleduetothedirtofthefilters)and,atthesamevoltageof9.5V,thedefaultcasehasalowerlossofairflowcomparedtotherescaledone.
Pict. 7
Pict. 8
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
6/16
1.3 Potentiometer setting
RPot = Rx + Ry isthepotentiometerresistance.TheinputresistanceofthedriverisRLandthevoltagepowersupplyV+ = 10V
Connectingthepotentiometertothedriveranaloginput,thevoltagevalueis
RY / RPot = α representsthepositionofalinearpotentiometerandthepreviousformulaα2VINRPot + (10RL - VINRPot) - VINRL = 0
RPot = 10RL VIN10α2 +(10-VIN10)-VIN = 0
RPot = RL VINα2 +(10-VIN)α - VIN = 0
RPot=0,1RL VINα2 +(100-VIN)α - 10VIN = 0
ObservingthecaseRPot = 10RLat90%ofthepotenti-ometerpositiontheanalogvoltagevalueisstillbelow5Vandthereforeaveryhighsensibilitytoregulatetheanalogvoltagevalueintheremaining10%isrequired.ThisconsiderationmustbedoneespeciallywhenNfansareconnectedinparallelwhereRL parallel = RL/NTherefore,thechoiceofthepotentiometervalueisveryimportantbasingontheinputresistanceofthedriverused.Unfortunately,anotherlimitationwhenchoosingthepotentiometervaluecomesfromthemaxcurrent
suppliedbythe+10Vpowersupplyofthedrivers.Inthiscasethemaxavailablecurrentis5mA,abovethisvaluethereisasignificantvoltagedrop,thereforetheminimumpotenti-ometervaluecanbeRPot=2kΩ.
Pict. 9
Pict. 10
Pict. 11
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
7/16
2. SENSORLESS CONSTANT PRESSURE
InthisparagraphthereisanapproximateexplanationaboutwhytheSensorlessConstantPressureisnotapplicableunlessseveralcompromisesareaccepted.
AlltheairflowsystemsareassumedtobecoherentwiththeapproximateformulaP = kQ2
Forthisanalysis,asimpleanalogywithelectricalcomponentscanbeconsidered:thesumoftheAirflowsinanodeofthesystemisequalto0andthesumofthePressuresinaclosednetworkisalsoequalto0.
and
Hereareusedthesymbols:
Loads(channels)
Variableloads(filters)
ConstantPressure
Generator
ConstantAirflow
Generator
StaticPressure = 0
Pict. 13
Consideringthemodeloffigure12thecorrespondingschemewhenthefanisworkinginconstantairflowmodeisshowninfigure14.Thefancankeeptheairflowconstant(Qconst = Q0)alongthenetindependentlyfromloadconditions.Usingthelawatthenodes:
Pict. 12
Pict. 14
The R1 and R2arenotvariableloads.Therefore,Q1 and Q2 are constant too.Proceedingwiththesquareoftheequation:
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
8/16
Usingthelawatthenetworks:
Assuming:
ThefanworkskeepingQ0 = const and changing its ΔPFanConsideringnowthesamemodelbutwiththefanworkinginconstantpressuremodeshowninpicture15:
Pict. 15
ThefancanbeprogrammedinthelabtokeeptheΔPFan =constGenerally,thefaninNicotra Gebhardtlaboratoryistestedfreeinletandductedoutlet.However,withoutknowing thefinalapplication for theconstantpressure, it shouldbetestedatfreeinletandfreeoutlet.
2.1 Considerations
ThepressureinallthepointsoftheinstallationmustbecalculatedfromtheΔPFanknowingalltheloadvaluesofthefinalinstallation.
changesand,therefore,P1cannotbekeptconstant.
AsolutionshouldbetocreateacustomizedsensorlessconstantpressureunitΔPFan = const(seepict.16)(ThiswouldalsoimplythateachcustomershouldhavetosendeachunitmodeltoNicotra Gebhardtlaboratoryformeasurements).
Pict. 16
Attimet=t0alldataofcustomers’unitsareacquiredwhenthevalueofRf is Rfs0
Therefore
ForaspecificloadconditionRinstall = RXthefanalgorithmworksonthevalue
Attimet=t1thestatusofthefiltersarechangedintoRft1andinthesameloadconditionRX,sothefanisnotabletodiscriminatethischange:
ThismeansthatthepressureP1graduallydecreasesdependingonthestatusofthefilters.
2.2 Conclusion
Thesensorlessconstantpressurecannotbeguaranteedand,therefore,notimplementedintotheNicotra Gebhardt products.
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
9/16
3. SENSORLESS CONSTANT AIRFLOW
ThefanworkinginConstantAirflowmodeisideallyageneratorabletomaintainthesameairflowindependentlyfromtheappliedload(pict.17).
Pict. 17
PLoad changes depending on RLoadandinfigure17isshowntheidealbehaviorfromaworkingpointAtoB.ThestepresponseinarealsystemwhenRLoadissuddenlyincreasedfirstandthensuddenlydecreasedtothestartingvalueisshowninfigure18.TheSensorlessConstantAirflowAlgorithmofthefanworksintermsofSpeed(SX)andPower(WX).
STEP UP1)Atthebeginning,thedutypointA -> (SA , WA)correspondstothedefinedairflowvalueQconst2)FromA to A’thecontrolhadnoenoughtimetoreact.Therefore,thespeedisthesame3)InA’theabsorbedpowerislower.Therefore,A’ -> (SA , WA’)correspondingtoadifferentvalueofQ4)ThecontrolincreasesthespeeduptodutypointB -> (SB , WB) corresponding again to Qconst value
STEP DOWN1)Atthebeginning,thedutypointB -> (SB , WB)correspondstothedefinedairflowvalueQconst2)FromB to B’thecontrolhadnoenoughtimetoreact.Therefore,thespeedisthesame3)InB’theabsorbedpowerishigher.Therefore,B’ -> (SB , WB’)correspondingtoadifferentvalueofQ4)ThecontrolincreasesthespeeduptodutypointA -> (SA , WA) corresponding again to Qconst value
Pict. 18
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
10/16
4. MASTER & SLAVE CONSIDERATIONS
Whentwofans(A and B)areputinparallel,configuredinconstantairflowmodeandbothblowinginthesameplenum,theyin-fluenceeachother.
Ifthefan a isperturbedforanyreason(ex.byobstructingtheinletcone),itbehaveslikethestep-upcasefrom1a to 2a.However,thebfanreactsasthestep-downcase(pict.21)from1b to 2b.
Pict. 19
Pict. 20
Pict. 21
Whentheobstructionisremovedfrompoint3, the afanwouldreturntothestartingpoint,butthetwofanswouldinterfereeachother.TheMaster&SlavemodeavoidsthisdeepinstabilitybecausetheMasterworksinclosedcontrolloop,whiletheSlaveworksinopenloopdrivenbytheMaster.
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
11/16
4.1 Characteristic of two forward curved fans in parallel at same speed
Twofansinparallelrunningatthesamespeedandblowinginthesameplenumworkatthesamepressure.
Pict. 22
Lookingatthecharacteristiccurveofaforwardcurvedfan,atthesamepressuretherearethreepossibleairflowpointsforeachfan:twostablepointsandtheunstableinflectionarea.
Pict. 23
Startingfromatotallyclosedplenumdampertoatotallyopenone,thetwofanshavethesameloadcurveuntiltheminimumpressurepointand,atalatertime,aper-turbationcouldforcethetwofanstohavetwopossibledifferentstates.
Pict. 24
Thesamehappensfromtotallyopentototallyclosedplenumdamper,butinthiscasethetwofanshavethesameloadcurveuntilthepointcorrespondingtotheminimumpressure.
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
12/16
Thepreviousassumptionistrueifthespeedsofthetwofansarethesame.IfforsomereasonstheSlaveisslowerthantheMaster,thereisaunbalanceconditionforcingthesystemtoadefinitestateasshowninpicture25.
Pict. 25
Thesamehappenswhentheslaverunsathigherspeed,evenif,inthiscase,theslavepointisforcedontheright.
5. PID TUNING PROCEDURE
BelowaredescribedsomefastrulestosetthePIDparameters,accordingtotheZiegler-Nichols method.
Itisapracticalproceduretofindtheso-called"criticalgain",fromwhichtheotherPIDparameterswillbederived.
1) Connectthetransduceroutputwirestotheinputconnectorsofthedriver“GND”e“IN”(or“TRANSDUCERINPUT”).2) Ifthefactorysettingofthefanmaximumspeedistoohighforyourinstallation,adjustthemaximumspeedtoamore
appropriate value.3) Determinethecorrectvalueofthesignalfromthetransducer(between0and10V)correspondingtothedesiredvalue
ofthemeasuredquantity(ifitispressure,temperature,airvelocity,COconcentrationorwhatever).Thisvaluemaybecalculatedknowingthefull-scalereadingofthetransducerandthedesiredvalue,orsimplyreadinINPUT REGISTER 30,withthefanrunninginaplainspeedcontrolmode,andadjustedtoachievethedesiredconditionofthecontrolledsystem.
4) SetthedriveroperatingmodebysettingtheHOLDING REGISTER 34tothecorrectvalueof“INPUT TYPE”:a. 10(PIDmodewithreferencetotheAnalogueinputsignal),b. 11(PIDmodewithreferencetothevolatileregisterHOLDING REGISTER 66)orc. 12(PIDmodewithreferencetothepermanentregisterHOLDING REGISTER 50).
5) Setthetargetvalueforthetransducerinputsignal,accordingtothechosenPIDoperatingmode:a. IfINPUT TYPE = 10,adjustthepotentiometeroutput,usingamultimeterofsimplyreadingthevalueof INPUT
REGISTER 29tothesamevaluedesiredfromthetransducer,b. IfINPUT TYPE = 11,setthedesiredvalueintheHOLDING REGISTER 66,c. IfINPUT TYPE = 12,setthedesiredvalueintheHOLDING REGISTER 50.
6) SettheTPIDtimeconstanttoaplausiblevalueforthesystemresponsetime,e.g.:a. Holding Register 54=100(=100ms).
7) Theprocessmustinitiallybecontrolledbyanexclusivelyproportionalcontroller;setKI and KDtozerobysettingup:a. Holding Register 52 = 0b. Holding Register 53 = 0
8) TheKPgainoftheproportionalcontrollerisgraduallyadjusted(preferablyfromalowvalue,whichisprogressivelyincreased)untilthefanspeedoscillateswithaconstantperiodandamplitudeoftheoscillations:a. Set Holding Register 51=100;b. Ifthefanacceleratesdirectlytoitsmaximumspeedoroscillateswithaprogressivelyincreasingamplitude,reduce
thevalueofthegaininHOLDING REGISTER 51 andtryagain;
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
13/16
6. REPLACEMENT OF A FORWARD CURVED FAN EQUIPPED WITH AN ACIM MOTOR WITH A DDMP FAN
ThischapterdescribeshowtoconfigureaDDMPfaninordertohavethesameperformanceofanoldfanequippedwithanACIMmotorthatmustbereplaced.Herearethestepstofollow:1) Checktheperformancecurveofthefantobereplaced->itmustbeaportionofthemaxperformancecurveofthechosen
DDMPasshowninpict.29.
Pict. 29
2) ChoosetwoloadcurvesfromtheACfanperformancecurve: a. Towardsfreeoutlet->i.e.:1700m3/h@50Pa b. Closetotheinflection->i.e.:1100m3/h@220Pa
3) UsingtheNGsoftware,itispossibletoconfiguretheDDMPfanandcheckitsperformanceand: a. Putthefaninafreeoutletcondition b. ConfiguretheoperatingmodeasModbusSpeedControl c. SetthespeedtoachieveapproximatelytheperformanceoftheACfanatfreeoutlet
c. If thefanslowsdownto itsminimumspeed,stabilizestoaconstantvalue,oroscillateswithaprogressivelyreducingamplitude,slowlyincreasethevalueofHOLDING REGISTER 51andtryagainuntilstableoscillationisachieved.
9) ThecriticalgainKuisthevalueofthegainforwhichthecontrolledvariablehassustainedoscillations,thatis,oscillationswhichdonotdisappearafteratransient:thisisameasureoftheeffectofthedelaysandthedynamicsoftheprocess.
10) RecordthecriticalperiodTuofsustainedoscillations,e.g.bymeasuringthetimerequiredfortencompleteoscillations,andthencalculatetheaverageoscillationperiod.
11) TheconstantsforthePIDcontrolleraredeterminedaccordingtothefollowingtable,tryingfirsttheclassic"classicPID"setting(firstlineinthetable):
Ziegler-Nichols method:
Control type Kp Ti Td Ki Kd
Classic PID 0.6 KU TU /2 TU /8 1.2 KU /TU 3 KU TU /40
Pessen Integral Rule 7 KU /10 2 TU /5 3 TU /20 1.75 KU /TU 21 KU TU /200
Some overshoot KU /3 TU /2 TU /3 0.666 KU /TU KU TU /9
No overshoot KU /5 TU /2 TU /3 (2/5)KU /TU KU TU /15
12) Settheregistervalueswiththecalculatedvaluesofthethreecontrolconstants,KP,KI and KD:a. Holding Register 51 = Kpb. Holding Register 52 = KIc. Holding Register 53 = KD
13) Ifthesystembehaviorusingthisfirstsetupisnotsatisfactory,trytheotherthreesettingsshowninthetable.
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
14/16
Pict. 30
4) ReadthemotorcurrentvalueandsettheequivalentHoldingRegister.ThiswillbethemaxcurrentlimitoftheDDMP.
5) ClosetheDDMPfanoutletuntiltheloadcurveisclosetothepointaftertheinflectionandincreasethespeeduntiltheACfanequivalentworkingpointisreached.
Pict. 31
Pict. 32
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
15/16
7) ConfigurethefanoperatingmodeinoneofthethreepossibleAsynchronousemulationmodes.
8) VerifythatthefinalperformanceiscorrectbyclosingandopeningtheDDMPfanoutlet.
6) SetthemaxspeedvalueinsidetherelatedHoldingRegister.
Pict. 33
Pict. 34
Pict. 35
Rev. 0 - 11/11/2020
ANNEXANNEXENEN
16/16
Regal Beloit Italy S.p.A.
Via Modena, 1824040 Ciserano (BG) ITALYPhone +39 035 873 111Fax +39 035 884 319www.regalbeloit.com