GEPID.docx

GEPID.docx

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GEPID

PID—Part1of3—（Part2|Part3）

Overview|Operands|ReferenceArrayParameters|Operation|SettingUserParameters|Example|CPUSupport

Overview

TheProportionalIntegralDerivative（PID）built-infunctionblockisageneralpurposealgorithmusedforclosed-loopprocesscontrol.Whenitreceivespowerflowthroughacontact,thePIDbuilt-infunctionblockcomparesaProcessVariable（PV）feedbackwithadesiredprocessSetPoint（SP）andupdatesaControlVariable（CV）outputbasedontheerror.

ThePIDbuilt-infunctionblockusesPIDloopgainsandotherparametersstoredintheReferenceArray,a40-WORDarray,tosolvethePIDalgorithmatthedesiredtimeinterval.Allparametersare16-bitWORDsforcompatibilitywith16-bitanalogprocessvariables.Thisallows%AImemorytobeusedforinputProcessVariablesand%AQtobeusedforoutputControlVariables.

Asscaled16-bitintegernumbers,manyparametersmustbedefinedineitherPVcountsorunits,orCVcountsorunits.Forexample,theSPinputmustbescaledoverthesamerangeasPVbecausethePIDbuilt-infunctionblockcalculatestheerrorfromthedifferenceofthesetwoinputs.ThePVandCVcountscanrangefrom-32768or0to+32767,matchinganalogscaling,orfrom0to10000,todisplayvariablesas0.00%to100.00%.ThePVandCVCountsdonothavetohavethesamescaling,inwhichcasetherewillbescalefactorsincludedinthePIDgains.

Thepowerflowoutputisenergizedwhenthebuilt-infunctionblockisperformedwithoutcalculationerror.Ifatleastonecalculationerrorexists,thereisnopowerflowoutput.

Note:

PIDdoesnotexecutemoreoftenthanonceevery10milliseconds.Thiscouldchangeyourresultsifyousetituptoexecuteeveryscanandthescanislessthan10milliseconds.Insuchacase,PIDdoesnotrununtilenoughscanshaveoccurredtoaccumulateanelapsedtimeof10milliseconds.Forexample,ifthescantimeis9milliseconds,PIDexecuteseveryotherscanwithanelapsedtimeof18millisecondsforeverytimeitexecutes.

Operands

Operand

DataType

MemoryArea

Description

?

?

?

?

one-dimensionalWORDarrayof40words

R,P,L,W,symbolic

Thisisa40-wordarray:

theReferenceArray.ThisisthePIDbuilt-infunctionblockcontrolinformation,whichcontainsbothuserandinternalparameters.The40consecutivewordsmustnotbeshared.

SP

INTvariableorconstant;BOOLarrayoflength16ormore（restrictionsapply）

dataflow,I,Q,M,T,G,R,P,L,AI,AQ,W,symbolic,I/Ovariable

ThecontrollooporprocessSetPoint.ComparingthePVCountstoSP,PIDadjuststheoutputCVsothatPVmatchesSP（zeroerror）.

PV

INTvariable;BOOLarrayoflength16ormore（restrictionsapply）

dataflow,I,Q,M,T,G,R,P,L,AI,AQ,W,symbolic,I/Ovariable

ThecontrolloopProcessVariableinput.MustbescaledoverthesamerangeasSP.Oftena%AIinput.

MAN

Powerflow

Manualmodeindicator.Whenenergizedto1（throughacontact）,thePIDbuilt-infunctionblockisinManualmode.IfMANisnotenergized（0）,thePIDbuilt-infunctionblockisinAutomaticmode.

UP

Powerflow

IfenergizedalongwithMAN,UPadjuststheCVupby1CVpersolution,thatis,1CVperaccesstothePIDbuilt-infunctionblock.

DN

Powerflow

IfenergizedalongwithMAN,DNadjuststheCVdownby1CVpersolution,thatis,1CVperaccesstothePIDbuilt-infunctionblock.

CV

INTvariable;BOOLarrayoflength16ormore（restrictionsapply）

dataflow,I,Q,M,T,G,R,P,L,AI,AQ,W,symbolic,I/Ovariable

TheControlVariableoutputtotheprocess.Oftena%AQanalogoutput.

ReferenceArrayParameters

BesidesthetwoinputwordsandthethreeManualcontrolcontacts,thePIDbuilt-infunctionblockrequires13user-definedparametersintheReferenceArray.Theseparametersmustbesetbeforecallingthebuilt-infunctionblock.Theother27parametersareusedbytheControllerandarenon-configurable.The%RefshowninthetablebelowisthebeginningaddressoftheReferenceArray（the?

?

?

?

operand）.Thenumberaftertheplussignistheoffsetinthearray.Forexample,iftheReferenceArraystartsat%R100,%R113containstheManualCommand（%Ref+0013）usedtosettheControlVariableandtheintegratorinManualmode.

Note:

TheReferenceArraymustbe%R,%P,or%Lregisters.EveryPIDbuilt-infunctionblockinthelogicmustuseadifferent40-wordarrayevenifall13userparametersarethesame,becauseotherwordsinthearrayareusedforinternalPIDdatastorage.Ensurethatthereareatleast40%R,%P,or%Lregistersbetweenthestartingreferenceaddressandthehighestconfigurable%R,%P,or%Lregister.

RegisterandParameter

LowBitUnitsandRangeofValues

Description

%REF+0000

LoopNumber

UINT.0to255

Optional.Loopnumber;numberofthePIDbuilt-infunctionblock.Foruserdisplayonly.ProvidesacommonidentificationintheControllerwiththeloopnumberdefinedbyanoperatorinterfacedevice.

Note:

Theloopnumberisdisplayedunderthebuilt-infunctionblockaddresswhenlogicismonitoredfromtheLDeditor.

%REF+0001

Algorithm

UINT.Non-configurable.SetandmaintainedbytheController.

1=ISAalgorithm（PID_ISA）

2=Independentalgorithm（PID_IND）

%REF+0002

SamplePeriod

Lowbitsetat1represents10ms.UINT.Range:

0（everyscan）to65,535（10.9Min）.

Theshortesttimein10msincrements,betweensolutionsofthePIDalgorithm.Forexample,usea10fora100mssampleperiod.

IfSamplePeriodis0,thealgorithmissolvedeverytimePIDiscalled,unlessthescanisunder10ms.SeeSamplePeriodandPIDScheduling.

ThePIDalgorithmissolvedonlyifthecurrentControllerelapsedtimeclockisatorlaterthanthelastPIDsolutiontimeplusthisSamplePeriod.

PIDcompensatesfortheactualtimeelapsedsincethelastexecution,within100microseconds.

%REF+0003

DeadBand+

PVCounts.0to32767（nevernegative）

Integer（INT）valuesdefiningtheupper（+）andlower（-）DeadBandlimitsinPVCounts.IfnoDeadBandisrequired,thesevaluesmustbe0.IfthePIDError（SP–PV）or（PV-SP）isabovethe（-）valueandbelowthe（+）value,thePIDcalculationsaresolvedwithanErrorof0.

Ifnon-zero,the（+）valuemustbegreaterthan0andthe（-）valuelessthan0orthePIDbuilt-infunctionblockwillnotwork.

Tip:

Leavetheseat0untilthePIDloopgainsaresetuportuned.Afterthat,aDeadBandmightbeaddedtoavoidsmallCVoutputchangesduetovariationsinerror,perhapstoreducemechanicalwear.

Note:

TheDeadbandActionbitdetermineshowPIDusesthedeadbandlimits.

%REF+0004

DeadBand—

PVCounts.-32768to0（neverpositive）

%REF+0005

InthePID_INDalgorithm,thiswordstorestheProportionalGain,Kp

InthePID_ISAalgorithm,thiswordstorestheControllergain,Kc

Lowbitsetat1represents1%of（CV%）/（PV%）.Rangeofrepresentedvalues:

0to327.67%

ThechangeintheCVinCVCountsfora100PVCountchangeintheErrorTerm.Itisdisplayedas0.00%/%withanimplieddecimalpointof2.AKporKcenteredas450isdisplayedas4.50andresultsina（Kp*Error/100）or（Kc*Error/100）=（450*Error/100）contributiontothePIDOutput.

Tip:

WhenthePID_INDalgorithmisused,KpisgenerallythefirstgainsettoadjustaPIDloop,aPDloop（Proportional–Derivative）oraPIloop（Proportional–Integral,whichisrarelyused）.UsingKpbyitselfmaybesufficienttocontrolcertaintypesofprocesses.

%REF+0006

DerivativeGain–Kd

Lowbitsetat1represents0.01seconds.Integer.Rangeofrepresentedvalues:

0to327.67sec.

ThechangeintheCVinCVCountsiftheErrororPVchanges1PVCountevery10ms.Enteredasatimewiththelowbitindicating10ms,itisdisplayedas0.00secondswithanimplieddecimalpointof2.Forexample,aKdenteredas120isdisplayedas1.20Secandresultsina[Kd*（deltaError）/（deltatime）]=（120*4/3）contributiontothePIDOutputifErrorwaschangingby4PVCountsevery30ms.

Tip:

WhenthePID_INDalgorithmisused,Kdcanbeusedtospeedupaslowloopresponse,butisverysensitivetoPVinputnoise.（OnPACSystems,youcanalleviatenoisesensitivitybyusingthederivativefilter,whichisenabledbysettingbit5oftheConfigWord.）Insomeprocesses,youcanomitKdandcontroltheprocessbyusingKpbyitselforKpincombinationwithKi.

%REF+0007

IntegralRate–Ki

Lowbitsetat1represents1repeat/1000seconds.Integervalues,0to32,767,representingthevalues0to32.767repeats/sec

ThechangeintheCVinCVCountsiftheErrorisaconstant1PVCount.Displayedas0.000Repeats/Secwithanimplieddecimalpointof3.Forexample,aKienteredas1400isdisplayedas1.400Repeats/Secandresultsina（Ki*Error*dt）=（1400*20*50/1000）contributiontoPIDOutputforanErrorof20PVCountsanda50msControllerscantime（SamplePeriodof0）.

Tip:

WhenthePID_INDalgorithmisused,KiisusuallythesecondgainsetinaPIDloop,Kpbeingthefirstgainset.KicanbeomittedentirelyinaPD（Proportional–Derivative）looporP（Proportionalonly）loop.Kiprovidesinertiatothecontrolsystem,thatis,itactsasanautomaticbias.

%REF+0008

CVBias/OutputOffset

CVCounts.Integer,-32768to+32767（addtointegratoroutput）

NumberofCVCountsaddedtothePIDOutputbeforetherateandamplitudeclamps.Canbeusedtosetnon-zeroCVvaluesifonlyKpProportionalgainsareused,orforfeedforwardcontrolofthisPIDloopoutputfromanothercontrolloop.

Forexample,ifyouwanttoletthebuilt-infunctionblockregulateerroraroundtheoutputmidpoint,settheBiastothemidpointoftherange.Forexample,forafullrange0through+32,767,+16,383isthemidpoint.

Note:

InthePID_INDalgorithm,Kiactsasanauto