EC FANS ANNEX - Nicotra Gebhardt

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Rev. 0 - 11/11/2020 EC FANS ANNEX Regal Beloit Italy S.p.A. Via Modena, 18 24040 Ciserano (BG) ITALY Phone +39 035 873 111 Fax +39 035 884 319 www.regalbeloit.com

Transcript of EC FANS ANNEX - Nicotra Gebhardt

Page 1: 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

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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

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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

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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

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Thesituationafterrescalingthespeedisshowninthefollowingfigure:

Therescalingobviouslyaffectsthebehaviorincaseofchangeofthefanload(forexampleduetothedirtofthefilters)and,atthesamevoltageof9.5V,thedefaultcasehasalowerlossofairflowcomparedtotherescaledone.

Pict. 7

Pict. 8

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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

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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:

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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.

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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

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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.

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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.

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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;

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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.

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Pict. 30

4) ReadthemotorcurrentvalueandsettheequivalentHoldingRegister.ThiswillbethemaxcurrentlimitoftheDDMP.

5) ClosetheDDMPfanoutletuntiltheloadcurveisclosetothepointaftertheinflectionandincreasethespeeduntiltheACfanequivalentworkingpointisreached.

Pict. 31

Pict. 32

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7) ConfigurethefanoperatingmodeinoneofthethreepossibleAsynchronousemulationmodes.

8) VerifythatthefinalperformanceiscorrectbyclosingandopeningtheDDMPfanoutlet.

6) SetthemaxspeedvalueinsidetherelatedHoldingRegister.

Pict. 33

Pict. 34

Pict. 35

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Regal Beloit Italy S.p.A.

Via Modena, 1824040 Ciserano (BG) ITALYPhone +39 035 873 111Fax +39 035 884 319www.regalbeloit.com