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DEREK ATHERTON CONTROL ENGINEERING AN INTRODUCTION WITH THE USE OF MATLAB DOWNLOAD FREE TEXTBOOKS AT BOOKBOON.COM Derek Atherton Control Engineering Download free books at BookBooN.com 2 Control Engineering © 2009 Derek Atherton & Ventus Publishing ApS ISBN 978-87-7681-466-3 Download free books at BookBooN.com 3 Control Engineering Contents Contents Preface 8 About the author 10 1. Introduction 11 1.1 What is Control Engineering? 11 1.2 Contents of the Book 13 1.3 References 15 2. Mathematical Model Representations of Linear Dynamical Systems 16 2.1 Introduction 16 2.2 The Laplace Transform and Transfer Functions 17 2.3 State space representations 20 2.4 Mathematical Models in MATLAB 23 2.5 Interconnecting Models in MATLAB 26 2.6 Reference 28 3. Transfer Functions and Their Responses 29 3.1 Introduction 29 3.2 Step Responses of Some Speciﬁ c Transfer Functions 30 3.3 Response to a Sinusoid 36 what‘s missing in this equation? rt e v d a e h k t c cli e s You could be one of our future talents a e Pl maeRsK inteRnationaL teChnoLogY & sCienCe PRogRamme Are you about to graduate as an engineer or geoscientist? Or have you already graduated? If so, there may be an exciting future for you with A.P. Moller - Maersk. www.maersk.com/mitas Download free books at BookBooN.com 4 Control Engineering Contents 40 4. Frequency Responses and Their Plotting 40 4.1 Introduction 40 4.2 Bode Diagram 46 4.3 Nyquist Plot 48 4.4 Nichols Plot 50 5. The Basic Feedback Loop 50 5.1 Introduction 51 5.2 The Closed Loop 52 5.3 System Speciﬁ cations 55 5.4 Stability 60 6. More on Analysis of the Closed Loop System 60 6.1 Introduction 60 6.2 Time Delay 61 6.3 The Root Locus 64 6.4 Relative Stability 68 6.5 M and N Circles 70 7. Classical Controller Design 70 7.1 Introduction 70 7.2 Phase Lead Design 77 7.3 Phase Lag Design 80 7.4 PID Control 90 rt e v d a e h k t c cli e s a e Pl Download free books at BookBooN.com 5 Control Engineering Contents 7.5 References 92 8. Parameter Optimisation for Fixed Controllers 92 8.1 Introduction 93 8.2 Some Simple Examples 96 8.3. Standard Forms 101 8.4 Control of an Unstable Plant 103 8.5 Further Comments 104 8.6 References 105 9. Further Controller Design Considerations 105 9.1 Introduction 105 9.2 Lag-Lead Compensation 107 9.3 Speed Control 109 9.4 Position Control 110 9.5 A Transfer Function with Complex Poles 114 9.6 The Effect of Parameter Variations 120 9.7 References 121 10. State Space Methods 121 10.1 Introduction 121 10.2 Solution of the State Equation 124 10.3 A State Transformation 124 10.4 State Representations of Transfer Functions 130 10.5. State Transformations between Different Forms 131 10.6 Evaluation of the State Transition Matrix www.job.oticon.dk Download free books at BookBooN.com 6 Control Engineering Contents 133 10.7 Controllability and Observability 134 10.8 Cascade Connection 135 11. Some State Space Design Methods 135 11.1 Introduction 136 11.2 State Variable Feedback 138 11.3 Linear Quadratic Regulator Problem 139 11.4 State Variable Feedback for Standard Forms 144 11.5 Transfer Function with Complex Poles 147 Appendix A 152 Appendix B 154 Appendix C 155 Appendix D rt e v d a e h k t c cli e s a e Pl Download free books at BookBooN.com 7 Control Engineering Preface Preface Control engineering courses have been given in universities for over fifty years. In fact it is just fifty years since I gave my first lectures on the subject. The basic theoretical topics taught in what is now often referred to as classical control have changed little over these years, but the tools which can be used to support theoretical analysis and the technologies used in control systems implementation have changed beyond recognition. I was lucky enough in the early days to have access to one of the first digital computers in a UK university, but programming was elementary, input was paper tape and output results, obtained often after a considerable delay, were just numbers on paper, which had to be laboriously plotted if one needed a graph. Simulations were done on analogue computers, which although having some nice features, had many deficiences. Today there are powerful digital simulation languages and specialised numerical software programs, which can be used on a desk top or lap top computer with excellent interaction and good graphical output. Although this book is not concerned with the technological implementation of control systems the technology has changed from components such as the vacuum tube, individual resistors and capacitors, and d.c commutator motors to integrated circuits, microprocessors, solid state power electronics and brushless machines. All of these are orders of magnitude cheaper, more robust, reliable and efficient. The majority of students graduating from engineering courses in universities will go on to work in industry where employers, if the company is to survive, will provide their employees doing analytical control system design with computers with appropriate computational software. The role of the university lecturer should therefore be to teach courses in such a way that the student knows enough detail about the concepts used that he can see whether results obtained are plausible, whilst leaving the computer to do the detailed analytical calculations. This has the advantage that more realistic problems can be studied, comparisons can easily be made between the results produced by alternative design approaches and hopefully the student can learn more about control engineering than worrying about doing mathematics. Many students, without doubt, are ‘turned off’ control engineering because of the perceived mathematical content and whilst further study on the theoretical aspects is required for prospective research students, they will be a small proportion of the class in a first course on control engineering. There are difficulties in this approach, as I am strongly of the opinion that student’s weaknesses in algebra have been caused by them not having carried out traditional procedures in arithmetic due to the adoption of calculators. However, I’m also sure there is a ‘happy medium’ somewhere. The use of modern software with simulation facilities allows the student to practice the interesting philosophy about doing engineering put forward in the book ‘Think, Play, Do’ by Dodgson et al OUP,2005. Download free books at BookBooN.com 8 Control Engineering Preface The material presented in this book has been set out with this philosophy in mind and it is hoped that it will enable the reader to obtain a sound knowledge of classical control system analytical design methods. Several software packages could have been used to support this approach but here MATLAB, which is the most widely used, has been employed. Sadly, however, if universities continue to use outdated examining methods where students are required to plot root locus, Nyquist diagrams etc. the reader may have to spend some additional time doing computations best done by a computer! Because I want to ‘get over’ ideas, understanding and concepts without detailed mathematics I have used words such as ‘it can be shown that’ to shorten some of the mathematical detail. This provides the reader interested in theory with the opportunity to do additional calculations. The first chapter provides a brief introduction to feedback control and then has a section reviewing the contents of the book, which will therefore not be repeated here. I am indebted to my recent former students Ali Boz and Nusret Tan for providing me with some diagrams, assistance with computations, reading the text and doing some of the research which has provided information and results on some of the topics covered. For over forty years I have benefitted greatly from discussions with and input from many research students, who are too numerous to name here but have all helped to enrich the learning experience. Finally, I would like to acknowledge the efforts of my friend Dr Karl Jones in reading through the manuscript and providing me with constructive feedback. I trust that few errors remain in the text and I’d appreciate feedback from any reader who finds any or has any questions on the contents. Derek P. Atherton Brighton, February 2009 Download free books at BookBooN.com 9 Control Engineering About the author About the author Professor Derek. P. Atherton BEng, PhD, DSc, CEng, FIEE, FIEEE, HonFInstMC, FRSA Derek Atherton studied at the universities of Sheffield and Manchester, obtaining a PhD in 1962 and DSc in 1975 from the latter. He spent the period from 1962 to 1980 teaching in Canada where he served on several National Research Council committees including the Electrical Engineering Grants Committee. He took up the post of Professor of Control Engineering at the University of Sussex in 1980 and is currently retired but has an office at the university, gives some lectures, and has the title of Emeritus Professor and Associate Tutor. He has been active with many professional engineering bodies, serving as President of the Institute of Measurement and Control in 1990, President of the IEEE Control Systems Society in 1995, being the only non North American to have held the position, and as a member of the IFAC Council from 1990-96. He served as an Editor of the IEE Proceedings on Control Theory and Applications (CTA) for several years until 2007 and was formerly an editor for the IEE Control Engineering Book Series. He has served EPSRC on research panels and as an assessor for research grants for many years and also served as a member of the Electrical Engineering Panel for the Research Assessment Exercise in 1992. His major research interests are in non-linear control theory, computer aided control system design, simulation and target tracking. He has written two books, is a co-author of two others and has published more than 350 papers in Journals and Conference Proceedings. Professor Atherton has given invited lectures in many countries and supervised over 30 Doctoral students. Derek P. Atherton. February 2009. Download free books at BookBooN.com 10