1.Introduction to Control System Engineering.pdf

A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial control systems which are used for controlling processes or machines. The control systems are designed via control engineering process.

1. 1
EEE 2221
Introduction to Control System Engineering
Nayeema Hasan
Lecturer
Dept. of EEE, KUET.
Reference Books:
‘Modern Control Engineering’-by Katsuhiko Ogata.

2. System
Asystemisacollectionofcomponentswhichinteractwitheachother
andwiththeenvironment(byinformationorenergylinks)fromwhich
thesystemisseparatedbyanotationalboundary.

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Systemsincludephysical,
biological,organizational,
andotherentities,and
combinationsthereof,which
canberepresentedthrough
acommonmathematical
symbolism.Thestudyof
feedbackcontrolsystemsis
essentiallyastudyofan
importantaspectofsystems
engineeringand its
application.

3. System
Input:Theinputisthestimulus,excitationorcommandappliedtoa
controlsystem.Typicallyfromexternalenergysource,usuallyinorder
toproduceaspecifiedresponsefromthecontrolsystem.
Output:Theoutputistheactualresponseobtainedfromacontrol
system.Itmayormaynotbeequaltospecifiedresponseimpliedbythe
input.
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4. Control Engineering
ControlengineeringorControlsystemsengineeringisbasedonthe
foundationsoffeedbacktheoryandlinearsystemanalysis,andit
integratestheconceptsofnetworktheoryandcommunicationtheory.
Itistheengineeringdisciplinethatappliescontroltheorytodesign
systemswithpredictablebehaviors.Thepracticeusessensorstomeasure
theoutputperformanceofthedevicebeingcontrolled(oftenavehicle)
andthosemeasurementscanbeusedtogivefeedbacktotheinput
actuatorsthatcanmakecorrectionstowarddesiredperformance.When
adeviceisdesignedtoperformwithouttheneedofhumaninputsfor
correctionitiscalledautomaticcontrol(suchascruisecontrolfor
regulatingacar'sspeed).Multi-disciplinaryinnature,controlsystems
engineeringactivitiesfocusonimplementationofcontrolsystemsmainly
derivedbymathematicalmodelingofsystemsofadiverserange.
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5. Why Control is important? [for production process/ in
plant]
(1)Safety:Preventinjurytoplantpersonnel,protecttheenvironmentby
preventingemissionandminimizingwasteandpreventdamagetothe
processequipment.
(2)Maintainproductquality(composition,purity,color,etc.)ona
continuousbasisandwithminimumcost.
(3)Maintainplantproductionrateatminimumcost.
So,wecansaythatthereasonsforautomationofprocessplantsareto
providesafetyandatsametimemaintaindesiredproductquality,high
plantthroughput,andreducedemandonhumanlabor.
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6. Control System
Acontrolsystemconsistsofsubsystemsandprocesses(orplants)
assembledforthepurposeofcontrollingtheoutputsoftheprocess.A
controlsystemisasystemcapableofmonitoringandregulatingthe
operationofaprocessoraplant.Forexample,afurnaceproducesheat
asaresultoftheflowoffuel.Inthisprocess,flowoffuelintheinput,
andheattobecontrolledistheoutput.
Therearetwocommonclassesofcontrolsystems,withmanyvariations
andcombinations:logicorsequentialcontrols,andfeedbackorlinear
controls.Thereisalsofuzzylogic,whichattemptstocombinesomeofthe
designsimplicityoflogicwiththeutilityoflinearcontrol.Somedevices
orsystemsareinherentlynotcontrollable
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7. Advantages of Control System
Webuildcontrolsystemsforfourprimaryreasons:
Poweramplification
Remotecontrol
Convenienceofinputform
Compensationofthedisturbances
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8. Analysis and Design Objectives of Control
System
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9. Analysis and Design Objectives of Control
System
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10. Classification of Control System
Controlsareclassifiedwithrespectto:
Techniqueinvolvedtoperformcontrol(i.e.human/machines):
i)manualcontrol
ii)automaticcontrol
Timedependenceofoutputvariable(i.e.constant/changing):
i)regulator/regulatingcontrol
ii)servo/trackingcontrol)
Fundamentalstructureofthecontrol(i.e.theinformationusedfor
computingthecontrol):
i)Openloopcontrol
ii)Feedbackcontrol/Closed-loopcontrol
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11. Classification of Control System
ManualandAutomaticControls-Examples
Asystemthatinvolves:
apersoncontrollingamachineiscalledmanualcontrol.Ex:Drivinga
car.
machinesonlyiscalledaautomaticcontrol.Ex:CentralAC
Servo/RegulatorControls–Examples
Anautomaticcontrolsystemdesignedto:
followachangingreferenceiscalledtrackingcontroloraservo.Ex:
Remotecontrolcar.
maintainanoutputfixed(regardlessofthedisturbancespresent)is
calledaregulatingcontroloraregulator.Ex:Cruisecontrol.
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12. Classification of Control System
Open-LoopControlandFeedbackcontrol:
Thestructuresarefundamentallydifferent:
Inanopen-loopcontrol,thesystemdoesNOTmeasuretheactual
outputandthereisnocorrectiontomakethatoutputconformtothe
desiredoutput.AnElectrictoasterisanopen-loopcontrol,Since:
Thecontrollerisbasedontheknowledge.
Theoutputisnotusedincontrolcomputation.
Inaclosedloopcontrol,thesystemincludesasensortomeasurethe
outputandusesfeedbackofthesensedvaluetoinfluencethecontrol
inputvariable.Awatertankofanordinaryflushtoiletisa(basic)
feedbackcontrol,sincetheoutputisfedbackforcontrolcomputation.
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13. Block Diagram
Itrepresentsthestructureofacontrolsystem.
Ithelpstoorganizethevariablesandequationsrepresentingthecontrol
system.
Itiscomposedof:
–boxes,thatrepresentsthecomponentsofthesystemincludingtheir
causality;
–Lineswitharrowsthatrepresentstheactualdynamicvariables,such
asspeed,pressure,velocity,etc.
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14. A simple open-loop Block Diagram example
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Spring/masssystem:
System=mass+spring:
•ControlInput:forceu
•Output:displacementx(t)
•Blockdiagram;derivedusing
Laplacetransforms.

15. Types of Block Diagram
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Blockdiagramsareoftwotypes:
i)SpecificComponentblockdiagram
ii)GenericComponentBlockDiagram
FortheSpring/masssystem:
SpecificComponentblockdiagram
GenericComponentblockdiagram

16. Definitions of Significant Terms
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•Process:Componentwhosetheoutputistobecontrolled,Ex:Mass.
•Actuator:Devicethatcaninfluencethecontrolinputvariableofthe
process,Ex:Spring.
•Plant=actuator+process,Ex:Spring/masssystem.
•Controlinput:externalvariable(signal/action)appliedtotheplant.
•Controller:computesthedesiredcontrolinputvariable
•Sensor:measurestheactualoutputvariableandconvertsthe
measuredoutputintoanelectricsignalforusebythecontroller.
•Comparator(orΣ)=computesthedifferencebetweenthedesired
andactualoutputvariablestogivethecontrollerameasureofthe
systemerror.
•Inputfilter=convertsthedesiredoutputvariabletoelectricformfor
latermanipulationbythecontroller.

17. Open-loop Control System
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•Open-loopcontrol:Anopen-loopcontrolisappliedtoachievedesired
systemresponseusingacontrolleroranactuatorwithoutfeedback.
Figurebelowistheblockdiagramofit:
FeaturesofOpen-loopControl:
Twooutstandingfeaturesofopen-loopcontrolsystemsare:
1.Theirabilitytoperformaccuratelyisdeterminedbytheircalibration.
Tocalibratemeanstoestablishorreestablishtheinput-outputrelation
toobtaindesiredsystemaccuracy.
2.Theyarenotusuallytroubledwithproblemsofinstability.

18. Example of an Open-loop Control System
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•Anopen-loopcontrolsystemutilizesanactuatingdevicetocontrol
theprocessdirectlywithoutusingfeedback.Belowaretheschematic
diagram(a)andblockdiagram(b)ofOpenloopspeed-controlofa
rotatingdisk.

19. Advantages of Open-loop Control System
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ThemainadvantagesofanopenLoopProductionControlSystemare:
•Simplicity:Itissimpleinconstructionanddesign.
•Low-cost:Itisinexpensivecomparedtoclosedloopcontrolsystems.
•EasyMaintenance:Itcostslesstimeandmoneytomaintain.
•Nomeasurement:Usefulwhentheproductionoutputisimpossibleor
hardtomeasure.
Toputitsimply,anopenloopcontrolsystemisbestformanufacturing
processesthatdonotrequireoutputchanges,runcheap,andcomewith
littletonowaystoquantifythemeasurement.Itshouldalsohavea
meagerchanceofdisruptionsduringtheproductionprocess.

20. Disadvantages of Open-loop Control System
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ThemaindisadvantagesofanopenLoopProductionControlSystem
are:
•Can’thandledisruptions:Itcanhardlyhandleanymajor
disruptions.
•PoorReliability:Itisunreliableasitcannotadapttouncertainties.
•PoorFlexibility:Itlackstheflexibilitytoself-correctandrecover
fromaccidentalstoppage.
•PoorAccuracy:Withnofeedbacksystem,itisveryinaccurate
whenitneedstoreflecttheactualmanufacturingoutput.

21. Examples of Open-loop Control System
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22. Closed Loop Control System
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•Closed-loopcontrol:Aclosed-loopcontrolisusedtoachievedesired
systemresponseusingacontrollerwiththeoutputmeasurementasa
feedbacksignal.
•Theuseoffeedbackenablesustoimprovesystemperformanceatthe
costofintroducingthemeasurementnoiseandstabilityproblem.
•Figurebelowistheblockdiagramofclosed-lopcontrolsystem:

23. Example of an Closed-loop Control System
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Aclosed-loopcontrolsystemusesameasurementoftheoutputand
feedbackofthissignaltocompareitwiththedesiredoutput.Belowarethe
schematicdiagram(a)andblockdiagram(b)ofClosedloopspeed-control
ofarotatingdisk.Thesystemisanegativefeedbackcontrolsystem.

24. Advantages of Closed-loop Control System
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•ReliableandAccurate:
•Itcanreflecttheactualproductionstatebyusingfeedbackasinput
data.
•FlexibleandFasterRecovery:
•Itcouldrecoverquickerfromdisruptionsandavoidfurtherdamage
toproductionefficiency.
•ContinuousImprovement:
•Collectedfeedbackcanbeanalyzedtostreamlinethemanufacturing
processfurther,savingtimeandoperationcosts.
•CombatRiskFactors:
•Systemwithwelldesignedfeedbackcontrolcanrespondto
unforeseenevents.
•Eliminatesneedforhumanadjustment:ofcontrolvariableand
reduceshumanworkload.
•Givesmuchbetterperformancethan:itispossiblewithopen-loop.

25. Disadvantages of Closed-loop Control System
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•Morecomplexthanopen-loopcontrol.
•Mayhavesteadystateerror.
•Dependsonaccuracywithwhichyoucanmeasuretheoutput.
•Maycausestabilityproblems.
•Requiredheavydocumentationorspreadsheetsmanagement.
•Softwaresolutionswereexpensiveandexclusive.
•Requiredcostlyandintensivetrainingforemployees.

26. Examples of Closed-loop Control System
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27. What is Feedback?
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•Feedbackisthatpropertyofaclosed-loopsystemwhichpermitsthe
output(orsomeothercontrolledvariable)tobecomparedwiththe
inputtothesystem(oraninputtosomeotherinternallysituated
componentorsubsystem)sothattheappropriatecontrolactionmay
beformedassomefunctionoftheoutputandinput.
•Moregenerally,feedbackissaidtoexistinasystemwhenaclosed
sequenceofcause-and-effectrelationsexistsbetweensystem
variables.

28. Characteristics of Feedback
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•CHARACTERISTICS OFFEEDBACK:
•1.Increasedaccuracy:Forexample,theabilitytofaithfully
reproducetheinput.
•2.Reducedsensitivity:oftheratioofoutputtoinputtovariationsin
systemparameters.
•3.Reducedeffectsofnonlinearities.
•4.Reducedeffectsofexternaldisturbancesornoise
•5.Increasedbandwidth:Thebandwidthofasystemisafrequency
responsemeasureofhowwellthesystemrespondsto(orfilters)
variations(orfrequencies)intheinputsignal

29. Example of a Closed-loop Control System
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Anexampleofaclosed-loopcontrolsystemisapersonsteeringan
automobile(assuminghiseyesareopen)bylookingattheauto’slocationon
theroadandmakingtheappropriateadjustments.
A person steering an automobile:

30. Example of a Closed-loop Control System
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Regulatetheleveloffluidbyadjustingtheoutputvalve:Theinputisa
referenceleveloffluidandismemorizedbyoperator.Thepoweramplifieris
theoperator.Thesensorisvisual.Operatorcomparestheactuallevelwith
thedesiredlevelandopensorclosesthevalve(actuator)adjustingthefluid
flowout,tomaintainthedesiredlevel.
.

31. Example of a Closed-loop Control System
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TemperatureControlSystem:
Thetemperatureintheelectricfurnaceismeasuredbyathermometer.
TheanalogtemperatureisconvertedtoadigitaltemperaturebyanA/D
converter.Thisdigitaltemperatureiscomparedwiththeprogrammed
inputtemperature,andifthereisanydiscrepancy(error),thecontroller
sendsoutasignaltotheheater,throughaninterface,amplifier,andrelay,
tobringthefurnacetemperaturetoadesiredvalue..

32. Example of a Closed-loop Control System
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TemperatureControlofpassengercompartmentofacar:
Figureaboveisafunctionalblockdiagramoftemperaturecontrolofthe
passengercompartmentofacar.Notethattheambienttemperatureand
radiationheattransferfromthesun,whicharenotconstantwhilethecar
isdriven,actasdisturbances.

33. Example of a Closed-loop Control System
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ControlSystemoftheNationalIncome:
It has become interesting and valuable to attempt to model the feedback
processes prevalent in the social, economic, and political spheres.

34. Multi-variable Control System
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35. Open-loop vs. Closed Loop Control System
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1.FeedbackElement:
Anadvantageoftheclosedloopcontrolsystemisthefactthattheuseof
feedbackmakesthesystemresponserelativelyinsensitivetoexternal
disturbancesandinternalvariationsinsystemparameters.Itisthus
possibletouserelativelyinaccurateandinexpensivecomponentstoobtain
theaccuratecontrolofagivenplant,whereasdoingsoisimpossibleinthe
open-loopcase.
2.Stability:
Fromthepointofviewofstability,theopen-loopcontrolsystemiseasier
tobuildbecausesystemstabilityisnotamajorproblem.Ontheother
hand,stabilityisamajorproblemintheclosed-loopcontrolsystem,which
maytendtoovercorrecterrorsandtherebycancauseoscillationsof
constantorchangingamplitude.

36. Open-loop vs. Closed Loop Control System
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3.CostandRequiredPower:
Notethattheoutputpowerratingpartiallydeterminesthecost,weight,
andsizeofacontrolsystem.Thenumberofcomponentsusedinaclosed-
loopcontrolsystemismorethanthatforacorrespondingopen-loop
controlsystem.Thus,theclosed-loopcontrolsystemisgenerallyhigherin
costandpower.Todecreasetherequiredpowerofasystem,open-loop
controlmaybeusedwhereapplicable.
Whentouseopen-loop:Itshouldbeemphasizedthatforsystemsinwhich
theinputsareknownaheadoftimeandinwhichthereareno
disturbancesitisadvisabletouseopen-loopcontrol.
Whentouseclosed-loop:Closedloopcontrolsystemshaveadvantages
onlywhenunpredictabledisturbancesand/orunpredictablevariationsin
systemcomponentsarepresent.
Apropercombinationofopen-loopandclosed-loopcontrolsisusuallyless
expensiveandwillgivesatisfactoryoverallsystemperformance.

37. Definitions
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•Servomechanism(oftenabbreviatedasservo).Thetermisoftenused
torefertoamechanicalsysteminwhichthesteady-stateerroriszero
foraconstantinputsignal.Sometimes,bygeneralization,itisusedto
refertoanyfeedbackcontrolsystem.
•Regulator.Thistermisusedtorefertosystemsinwhichthereisa
constantsteady-stateoutputforaconstantsignal.Thenameis
derivedfromtheearlyspeedandvoltagecontrols,calledspeedand
voltageregulators
•Commandinput:Themotivatinginputsignaltothesystem,whichis
independentoftheoutputofthesystemandexercisescomplete
controloverit(ifthesystemiscompletelycontrollable).
•Referenceselector(referenceinputelement).Theunitthatestablishes
thevalueofthereferenceinput.Thereferenceselectoriscalibratedin
termsofthedesiredvalueofthesystemoutput.

38. Definitions
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•Referenceinput.Thereferencesignalproducedbythereference
selector,i.e.,thecommandexpressedinaformdirectlyusablebythe
system.Itistheactualsignalinputtothecontrolsystem.
•Disturbanceinput.Anexternaldisturbanceinputsignaltothesystem
thathasanunwantedeffectonthesystemoutput.
•Forwardelement(systemdynamics):Theunitthatreactstoan
actuatingsignaltoproduceadesiredoutput.Thisunitdoesthework
ofcontrollingtheoutputandthusmaybeapoweramplifier.
Feedbackelement:Theunitthatprovidesthemeansforfeedingback
theoutputquantity,orafunctionoftheoutput,inordertocompare
itwiththereferenceinput.

39. Definitions
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•Output(controlledvariable).Thequantitythatmustbemaintained
ataprescribedvalue,i.e.,followingthecommandinputwithout
respondingthedisturbanceinputs.
•Actuatingsignal.=Referenceinput–feedbacksignal.Itistheinput
tothecontrolunitthatcausestheoutputtohavethedesiredvalue.
•Thefundamentaldifferencebetweentheopen-andclosed-loop
systemsisthefeedbackaction,whichmaybecontinuousor
discontinuous.Inoneformofdiscontinuouscontroltheinputand
outputquantitiesareperiodicallysampledanddiscontinuous.
Continuouscontrolimpliesthattheoutputiscontinuouslyfedback
andcomparedwiththereferenceinputcompared;i.e.,thecontrol
actionisdiscontinuousintime.Thisiscommonlycalledadigital,
discrete-dataorsampled-datafeedbackcontrolsystem.

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