Table Of ContentAdvances in Industrial Control
Other titles published in this Series:
NonlinearIdentificationand Control
GuopingLiu
DigitalControllerImplementationandFragility
RobertS.H.IstepanianandJamesF.Whidborne(Eds.)
OptimisationofIndustrialProcessesatSupervisoryLevel
DorisSa´ez,AldoCiprianoandAndrzejW.Ordys
AppliedPredictiveControl
HuangSunan,TanKokKiongandLeeTongHeng
HardDiskDriveServoSystems
BenM.Chen,TongH.LeeandVenkatakrishnanVenkataramanan
RobustControlofDieselShipPropulsion
NikolaosXiros
HydraulicServo-systems
MoheiddineJelaliandAndreasKroll
Model-basedFaultDiagnosisinDynamicSystemsUsingIdentificationTechniques
SilvioSimani,CesareFantuzziandRonJ.Patton
StrategiesforFeedbackLinearisation:ADynamicNeuralNetworkApproach
FreddyGarces,VictorM.Becerra,ChandrasekharKambhampatiand
KevinWarwick
RobustAutonomousGuidance
AlbertoIsidori,LorenzoMarconiandAndreaSerrani
DynamicModellingofGasTurbines
GennadyG.KulikovandHaydnA.Thompson(Eds.)
ControlofFuelCellPowerSystems
JayT.Pukrushpan,AnnaG.StefanopoulouandHueiPeng
FuzzyLogic,IdentificationandPredictiveControl
JairoEspinosa,JoosVanderwalleandVincentWertz
OptimalReal-timeControlofSewerNetworks
MagdaleneMarinakiandMarkosPapageorgiou
ComputationalIntelligenceinTimeSeriesForecasting
AjoyK.PalitandDobrivojePopovic
ModellingandControlofmini-FlyingMachines
PedroCastillo,RogelioLozanoandAlejandroDzul
RudderandFinShipRollStabilization
TristanPerez
ControlofPassengerTrafficSystemsinBuildings
SandorMarkon
PublicationdueJanuary2006
NonlinearH2/H∞Feedbackcontrol
MuradAbu-Khalaf,FrankL.LewisandJieJuang
PublicationdueJanuary2006
Benoˆıt Codrons
Process Modelling
for Control
A Unified Framework Using Standard Black-box
Techniques
With 74 Figures
Benoˆıt Codrons, Dr.Eng.
Laborelec, 125 Rue de Rhode, B-1630 Linkebeek, Belgium
BritishLibraryCataloguinginPublicationData
Codrons,Benoˆıt
Processmodellingforcontrol:aunifiedframeworkusing
standardblack-boxtechniques.—(Advancesinindustrial
control)
1.Processcontrol—Mathematicalmodels
I.Title
629.8′312
ISBN1852339187
LibraryofCongressControlNumber2005923269
Apartfromanyfairdealingforthepurposesofresearchorprivatestudy,orcriticismorreview,as
permittedundertheCopyright,DesignsandPatentsAct1988,thispublicationmayonlyberepro-
duced,storedortransmitted,inanyformorbyanymeans,withthepriorpermissioninwritingof
thepublishers,orinthecaseofreprographicreproductioninaccordancewiththetermsoflicences
issuedbytheCopyrightLicensingAgency.Enquiriesconcerningreproductionoutsidethoseterms
shouldbesenttothepublishers.
AdvancesinIndustrialControlseriesISSN1430-9491
ISBN1-85233-918-7SpringerLondonBerlinHeidelberg
SpringerScience+BusinessMedia
springeronline.com
©Springer-VerlagLondonLimited2005
PrintedintheUnitedStatesofAmerica
Theuseofregisterednames,trademarks,etc.inthispublicationdoesnotimply,evenintheabsence
of a specific statement, that such names are exempt from the relevant laws and regulations and
thereforefreeforgeneraluse.
Thepublishermakesnorepresentation,expressorimplied,withregardtotheaccuracyoftheinfor-
mationcontainedinthisbookandcannotacceptanylegalresponsibilityorliabilityforanyerrors
oromissionsthatmaybemade.
Typesetting:Electronictextfilespreparedbyauthor
69/3830-543210 Printedonacid-freepaper SPIN11009207
Advances in Industrial Control
SeriesEditors
ProfessorMichaelJ.Grimble,ProfessorofIndustrialSystemsandDirector
ProfessorMichaelA.Johnson,EmeritusProfessorofControlSystemsand
DeputyDirector
IndustrialControlCentre
DepartmentofElectronicandElectricalEngineering
UniversityofStrathclyde
GrahamHillsBuilding
50GeorgeStreet
GlasgowG11QE
UnitedKingdom
SeriesAdvisoryBoard
ProfessorE.F.Camacho
EscuelaSuperiordeIngenieros
UniversidaddeSevilla
CaminodelosDescobrimientoss/n
41092Sevilla
Spain
ProfessorS.Engell
LehrstuhlfrAnlagensteuerungstechnik
FachbereichChemietechnik
Universita¨tDortmund
44221Dortmund
Germany
ProfessorG.Goodwin
DepartmentofElectricalandComputerEngineering
TheUniversityofNewcastle
Callaghan
NSW2308
Australia
ProfessorT.J.Harris
DepartmentofChemicalEngineering
Queen’sUniversity
Kingston,Ontario
K7L3N6
Canada
ProfessorT.H.Lee
DepartmentofElectricalEngineering
NationalUniversityofSingapore
4EngineeringDrive3
Singapore117576
ProfessorEmeritusO.P.Malik
DepartmentofElectricalandComputerEngineering
UniversityofCalgary
2500,UniversityDrive,NW
Calgary
Alberta
T2N1N4
Canada
ProfessorK.-F.Man
ElectronicEngineeringDepartment
CityUniversityofHongKong
TatCheeAvenue
Kowloon
HongKong
ProfessorG.Olsson
DepartmentofIndustrialElectricalEngineeringandAutomation
LundInstituteofTechnology
Box118
S-22100Lund
Sweden
ProfessorA.Ray
PennsylvaniaStateUniversity
DepartmentofMechanicalEngineering
0329ReberBuilding
UniversityPark
PA16802
USA
ProfessorD.E.Seborg
ChemicalEngineering
3335EngineeringII
UniversityofCaliforniaSantaBarbara
SantaBarbara
CA93106
USA
DoctorI.Yamamoto
TechnicalHeadquarters
NagasakiResearch&DevelopmentCenter
MitsubishiHeavyIndustriesLtd
5-717-1,Fukahori-Machi
Nagasaki851-0392
Japan
Series Editors’ Foreword
The series Advances in Industrial Control aims to report and encourage
technology transfer in control engineering. The rapid development of control
technology has an impact on all areas of the control discipline. New theory,
new controllers, actuators, sensors, new industrial processes, computer meth-
ods, new applications, new philosophies..., new challenges. Much of this
development work resides in industrial reports, feasibility study papers and
the reports of advanced collaborative projects. The series offers an opportu-
nityfor researcherstopresent anextended expositionofsuch newworkin all
aspects of industrial control for wider and rapid dissemination.
Thestandardframeworkforprocessmodellingandcontroldesignhasbeen:
Determine nominal model – Validate model – Progress control design – Im-
plement controller. Benoıˆt Codrons brings new depth and insight to these
standard steps in this new Advances in Industrial Control monograph Pro-
cess Modelling for Control. His approach is to pose a searching set of ques-
tionsforeachcomponentofthemodelling – controlcycle.Thefirsttwochap-
ters set the scene for model identification including a short survey of transfer
function system representation, prediction-error identification and balanced
model truncation methods. This is followed by four investigative chapters
each constructed around answering some questions very pertinent to the use
of model identification for control design. As an example, look at Chapter 3
where the motivating question is simply: “How should we identify a model
(Gˆ, Hˆ) in such a way that it be good for control design?” Dr. Codrons then
presents a careful theoretical analysis and supporting examples to demon-
strate that “it is generally preferable to identify a (possible low-order) model
in closed loop when the purpose is to use the model for control design”. This
type of presentation is used to examine similar questions for the other stages
in the model identification – control design cycle. The mix of theory and
illustrative examples is used by Dr. Codrons to lead on to recommendations
andsetsofguidelinesthattheindustrialcontrolengineerwillfindinvaluable.
vii
viii SeriesEditors’Foreword
This new volume in the Advances in Industrial Control series has thor-
oughtheoreticalmaterialthatwillappealtotheacademiccontrolcommunity
lecturersandpostgraduatestudentsalike.Therhetoricalquestion-and-answer
style along with the provision of recommendations and guidelines will give
the industrial engineer and practitioner the motivation to consider and try
new approaches in the model identification field in industrial control. Hence
thevolumeisaverywelcomeadditiontotheAdvancesinIndustrialControl
monographserieswhichwehopewillencouragetheindustrialcontrolcommu-
nity to look anew at the current model identification paradigm.
M.J. Grimble and M.A. Johnson
Industrial Control Centre
Glasgow, Scotland, U.K.
Preface
The contents of this book are, for the most part, the result of the experience I
gained during the five years I spent as a researcher at the Centre for Sys-
tems Engineering and Applied Mechanics (CESAME), Universite´
catholique de Louvain, Belgium, from September 1995 to June 2000. I
am very grateful to Michel Gevers, Brian D.O. Anderson, Xavier Bombois and
FrankyDeBruyneforthegoodtimeswespent,thegreatideaswehadandthe
good work we did together. I also want to give credit to Pascale Bendotti and
Cl´ement-Marc Falinower of E´lectricite´ de France for their support and
collaboration in the elaboration of the case study in Chapter 6.
After completion of my Ph.D. thesis (Codrons, 2000), I landed in an indus-
trial R&D laboratory, fully loaded with scientific knowledge but with almost
no practical experience. This was the real beginning of the genesis of this
book. As I have spent the last four years discovering the industrial reality and
trying to put my theoretical knowledge into practice, I have also discovered
the gap that often separates both worlds. For instance, when the issue is the
realisation of identification tests on an industrial system in order to design or
tunesomecontroller, in aratheramusingway, both thescientistandtheplant
operator will recommend making the tests in closed loop. The latter, because
it is often more comfortable for him and less risky for plant operation than
open-loop tests; the former, for the reasons exposed in this book. In spite of
this, however, the usual practice consists of opening the loop, applying a step
on the input on the process, and measuring the output response from which
essentialvalueslikethedominanttimeconstantandthegainoftheprocesscan
be determined. What is the problem, then? Who is right? Is it the scientist
and his closed-loop... whim? Or is it the control or process engineer, with his
rules of good practice or her pragmatic approach? To be fair, both are prob-
ably right. The open-loop approach is satisfactory most of the time when the
objectiveistotunePIDcontrollers. grossomodo,thoseonlyrequireknowledge
ix
x Preface
of the processtime constant and gain for their tuning. However, this approach
deprives the engineer of the necessary knowledge of the process dynamics that
would help him to design more sophisticated control structures, especially in
thecaseofcoupledsubsystemsthatwouldrequireaglobalhandlingwithmulti-
variablecontrolsolutionsinlieuofmonovariablebutinteracting(andmutually
disturbing) PID loops.
The problem is even worse when the objective is to design a controller that
has to be simultaneously optimal (with respect to some performance indica-
tor, e.g., the variance of the output or an LQG criterion), robust (with respect
to modelling errors, disturbances, changes in operating conditions, etc.) and
implementable in an industrial control system (which will generally put a con-
straintonitsorderand/orcomplexity). Mostofthetime,suboptimalsolutions
are worked out on the basis of, again, monovariable control loops and some-
timesindecipherablelogicprogrammingaimedatmanagingtheworkingstatus
of the various PID controllers in function of the process conditions. This re-
sults, generally, from a lack of knowledge of the existing modelling and control
design tools, or of the way they can be used in industrial practice.
Actually,oneofthemostcriticalandbadlytunedloopsIhavebeenfacedwith
isprobablythelearningloopbetweenindustryandtheacademicworld. With-
out pretentiousness, my intention when starting to write of this book was to
make some of the most recent results in process modelling for control available
to the industrial community. The objective is twofold: firstly, it is to provide
the control engineer with the necessary theory on modelling for control using
somechosenspecificblack-boxtechniquesinalinear,time-invariantframework
(itsoundsareasonablefirststepbeforenonlineartechniquescanbeaddressed);
secondly,andthisisperhapsthemostimportantissue,itistoinitiateachange
is the way modelling and control problems are perceived and tackled in indus-
trial practice. This is just a small part of what a feed-forward action from
University to Industry might be. Also very important is the feedback from
Industry to Academia that happens essentially through collaborations.
Benoˆıt Codrons
Brussels, 1st September, 2004
