Table Of Content

IET conTrol EngInEErIng sErIEs 64 Series Editors: Professor D.P. Atherton Professor G.W. Irwin Control Theory 2nd Edition Other volumes in this series: Volume 2 Elevator traffic analysis, design and control, 2nd edition G.C. Barney and S.M. dos Santos Volume 8 A history of control engineering, 1800–1930 S. Bennett Volume 14 Optimal relay and saturating control system synthesis E.P. Ryan Volume 18 Applied control theory, 2nd edition J.R. Leigh Volume 20 Design of modern control systems D.J. Bell, P.A. Cook and N. Munro (Editors) Volume 28 Robots and automated manufacture J. Billingsley (Editor) Volume 30 Electromagnetic suspension: dynamics and control P.K. Sinha Volume 32 Multivariable control for industrial applications J. O’Reilly (Editor) Volume 33 Temperature measurement and control J.R. Leigh Volume 34 Singular perturbation methodology in control systems D.S. Naidu Volume 35 Implementation of self-tuning controllers K. Warwick (Editor) Volume 37 Industrial digital control systems, 2nd edition K. Warwick and D. Rees (Editors) Volume 38 Parallel processing in control P.J. Fleming (Editor) Volume 39 Continuous time controller design R. Balasubramanian Volume 40 Deterministic control of uncertain systems A.S.I. Zinober (Editor) Volume 41 Computer control of real-time processes S. Bennett and G.S. Virk (Editors) Volume 42 Digital signal processing: principles, devices and applications N.B. Jones and J.D.McK. Watson (Editors) Volume 43 Trends in information technology D.A. Linkens and R.I. Nicolson (Editors) Volume 44 Knowledge-based systems for industrial control J. McGhee, M.J. Grimble and A. Mowforth (Editors) Volume 47 A history of control engineering, 1930–1956 S. Bennett Volume 49 Polynomial methods in optimal control and filtering K.J. Hunt (Editor) Volume 50 Programming industrial control systems using IEC 1131-3 R.W. Lewis Volume 51 Advanced robotics and intelligent machines J.O. Gray and D.G. Caldwell (Editors) Volume 52 Adaptive prediction and predictive control P.P. Kanjilal Volume 53 Neural network applications in control G.W. Irwin, K. Warwick and K.J. Hunt (Editors) Volume 54 Control engineering solutions: a practical approach P. Albertos, R. Strietzel and N. Mort (Editors) Volume 55 Genetic algorithms in engineering systems A.M.S. Zalzala and P.J. Fleming (Editors) Volume 56 Symbolic methods in control system analysis and design N. Munro (Editor) Volume 57 Flight control systems R.W. Pratt (Editor) Volume 58 Power-plant control and instrumentation D. Lindsley Volume 59 Modelling control systems using IEC 61499 R. Lewis Volume 60 People in control: human factors in control room design J. Noyes and M. Bransby (Editors) Volume 61 Nonlinear predictive control: theory and practice B. Kouvaritakis and M. Cannon (Editors) Volume 62 Active sound and vibration control M.O. Tokhi and S.M. Veres Volume 63 Stepping motors: a guide to theory and practice, 4th edition P.P. Acarnley Volume 64 Control theory, 2nd edition J. R. Leigh Volume 65 Modelling and parameter estimation of dynamic systems J.R. Raol, G. Girija and J. Singh Volume 66 Variable structure systems: from principles to implementation A. Sabanovic, L. Fridman and S. Spurgeon (Editors) Volume 67 Motion vision: design of compact motion sensing solution for autonomous systems J. Kolodko and L. Vlacic Volume 68 Flexible robot manipulators: modelling, simulation and control M.O. Tokhi and A.K.M. Azad (Editors) Volume 69 Advances in unmanned marine vehicles G. Roberts and R. Sutton (Editors) Volume 70 Intelligent control systems using computational intelligence techniques A. Ruano (Editor) Control Theory 2nd Edition J.R. Leigh The Institution of Engineering and Technology Published by The Institution of Engineering and Technology, London, United Kingdom First edition © 2004 The Institution of Electrical Engineers New cover © 2008 The Institution of Engineering and Technology Hardback edition 2004 (0 86341 332 3) Paperback edition 2004 (0 86341 339 0) This publication is copyright under the Berne Convention and the Universal Copyright Convention. All rights reserved. Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act, 1988, this publication may be reproduced, stored or transmitted, in any form or by any means, only with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Inquiries concerning reproduction outside those terms should be sent to the publishers at the undermentioned address: The Institution of Engineering and Technology Michael Faraday House Six Hills Way, Stevenage Herts, SG1 2AY, United Kingdom www.theiet.org While the author and the publishers believe that the information and guidance given in this work are correct, all parties must rely upon their own skill and judgement when making use of them. Neither the author nor the publishers assume any liability to anyone for any loss or damage caused by any error or omission in the work, whether such error or omission is the result of negligence or any other cause. Any and all such liability is disclaimed. The moral right of the author to be identified as author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. British Library Cataloguing in Publication Data Leigh, J.R. (James Ronald), 1931 Control theory: a guided tour. – 2nd ed. – 1. Control theory 2. Automatic control I. Title 629.8’312 ISBN (10 digit) 0 86341 339 0 ISBN (13 digit) 978-0-86341-339-1 Typeset in India by Newgen Imaging Systems (P) Ltd, Chennai First printed in the UK by MPG Books Ltd, Bodmin, Cornwall Reprinted in the UK by Lightning Source UK Ltd, Milton Keynes To the colleagues who have enriched my professional life Contents Introductiontothesecondedition xvii Thestructure,contentandpurposeofthebook xix 1 Controlconcepts:anon-mathematicalintroduction 1 1.1 Generalsystemsideas 1 1.2 Whatiscontroltheory?–aninitialdiscussion 3 1.3 Whatisautomaticcontrol? 6 1.4 Someexamplesofcontrolsystems 8 2 Controldesignideas:anon-mathematicaltreatment 11 2.1 Initialdiscussion 11 2.2 Question:Canthebestpossiblecontrolactionsbesynthesised bysomemechanism? 12 2.3 Requirementsforanautomaticcontrolsystem 12 2.4 Automaticfeedbackcontrol 14 2.5 Diagramsillustratingandamplifyingsomeoftheconcepts describedsofarandshowingrelationshipstoasoftware engineeringcontext 14 3 Synthesisofautomaticfeedbackcontrolloops: amorequantitativeview 19 3.1 Feedbackloops:furtherdiscussion 19 3.2 Whatsortsofcontrollawsarethere? 21 3.3 Howfeedbackcontrolworks–apracticalview 22 3.4 Generalconditionsforthesuccessoffeedback controlstrategies 27 3.5 Alternativestofeedbackcontrol 28 viii Contents 4 HowtheLaplacetransformgreatlysimplifiessystem representationandmanipulation 29 4.1 Laplacetransformtechniques 29 4.2 DefinitionoftheLaplacetransform 29 4A ConvergenceoftheintegralthatdefinestheLaplace transform 30 − + 4B Problemswith0 and0 31 4.3 UseoftheLaplacetransformincontroltheory 31 4.4 Theconceptoftransferfunction 32 4.5 Systemsimplificationthroughblockmanipulation 32 4.6 Howatransferfunctioncanbeobtainedfrom adifferentialequation 33 4.7 Polesandzerosofatransferfunction 34 4.8 Understandingsystembehaviourfromaknowledgeof poleandzerolocationsinthecomplexplane 34 4.9 Poleplacement:synthesisofacontrollertoplacetheclosed looppolesindesirablepositions 38 4.10 Movingthepolesofaclosedloopsystemtodesirable locations–therootlocustechnique 39 4.11 Obtainingthetransferfunctionofaprocessfromeither afrequencyresponsecurveoratransientresponsecurve 40 4C Convolution–whatitis 41 4.12 Determinationoftransferfunctionsbycross-correlation 43 4D Calculationofresonantfrequenciesfromthepole–zero diagram 43 4E Derivationofaformulafordampednaturalfrequency 45 4F Therootlocusofasystemwithopen-looppolesandzeros locatedasinFigure4.19willincludeacirclecentredonthe zero 46 5 Frequencyresponsemethods 47 5.1 Introduction 47 5.2 Designusingfrequencyresponsemethods–initial explanation 47 5.3 Frequencyresponseofalinearsystem 48 5.4 TheBodediagram 48 5.5 Frequencyresponseandstability:animportantidea 49 5.6 Simpleexampleoftheuseoftheforegoingidea infeedbackloopdesign 50 5.7 Practicalpoint–theneedforstabilitymargins 51 5.8 Generalideaofcontroldesignusingfrequency responsemethods 51 5.9 Obtainingthefrequencyresponseofasystem experimentally–alistofdifficulties 52 Contents ix 5.10 Designbasedonknowledgeoftheresponseof asystemtoaunitstepinput 52 5.11 Howfrequencyresponseisobtainedbycalculation fromadifferentialequation 53 5.12 Frequencyresponsetestingcangiveagoodestimate ofasystem’stransferfunction 55 5.13 Frequencyresponseofasecondordersystem 56 5A Thefrequencyresponseofasystemwithpolesand/orzerosnear totheimaginaryaxis 58 5B Someinterestingandusefulideasthatwereoriginated byBode 58 5.14 NyquistdiagramandNicholschart 60 6 Mathematicalmodelling 61 6.1 Approachestomathematicalmodelling 61 6.2 Methodsforthedevelopmentofmathematicalmodels 62 6.3 Modellingasystemthatexists,basedondataobtained byexperimentation 62 6.4 Constructionofmodelsfromtheoreticalconsiderations 64 6.5 Methods/approaches/techniquesforparameterestimation 64 6.6 Whymodellingisdifficult–animportantdiscussion 66 6.7 Fixingofparameters 67 6.8 Parameterestimation 67 6.9 Regressionanalysis 67 6.10 Analysisofresiduals 68 6A Doubtandcertainty 68 6B Anticipatorysystems 70 6C Chaos 71 6D Mathematicalmodelling–somephilosophicalcomments 73 6E Astillrelevantillustrationofthedifficultyofmathematical modelling:thelongmarchtowardsdevelopingaquantitative understandingofthehumblewaterwheel,1590–1841 76 6F Apostscriptontheeffectivenessofthoughtexperiments 79 6G Experimentationonplantstoassistinmodeldevelopment–the teststhatyouneedmaynotbeinthetextbook! 79 7 Limitstoperformance 83 7.1 Stability–initialdiscussion 83 7A Stabilitytheory–alongtermthreadthatbinds 84 7.2 Stabilityforcontrolsystems–howitisquantified 86 7B TheingeniousmethodofHurwitz 88 7.3 Linearsystemstabilitytests 88 7.4 Stabilitymargin 88 7.5 Stabilitytestsfornon-linearsystems 89