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You are here : Control System Design - Index | Book Contents | Preface (English) PrefaceControl Engineering plays a fundamental role in modern technological systems. The benefits of improved control in industry can be immense. They include improved product quality, reduced energy consumption, minimization of waste material, increased safety levels, and reduction of pollution. A difficulty with the subject, however, is that some of the more advanced aspects depend on a sophisticated mathematical background. Arguably, mathematical systems theory is one of the most significant achievements of twentieth-century science, but its practical impact is only as important as the benefits it can bring. Thus, in this book, we aim to strike a balance which places strong emphasis on design. It was the authors' involvement in several industrial control system design projects that provided part of the motivation to write this book. In a typical industrial problem, we found ourselves investigating fluid and thermal dynamics, experiencing the detrimental effects of nonconstant PLC scan rates, dealing with system integration and network communication protocols, building trust with plant operators, and investigating safe bumpless transfer schemes for testing tentative control designs on potentially dangerous plants. In short, we experienced the day-to-day excitement, frustration, set-backs, and progress in getting advanced control to contribute to a commercial company's bottom line. This is not an easy task. Success in this type of venture typically depends on the application of a wide range of multidisciplinary skills; however, it is rewarding and exciting work for those who do it. One of the main aims of this book is to share this excitement with our readers. We hope to contribute to the development of skills and attitudes within readers and students that will better equip them to face the challenges of real-world design problems. The book is thus intended to contribute to the ongoing reform of the Control Engineering curriculum. This topic is receiving considerable international attention. For example, a recent issue of IEEE Control Systems Magazine features an entire special section devoted to this theme. Reforming the curriculum will not, however, be done by books alone - it will be done by people: students, teachers, researchers, practitioners, and publication and grant reviewers, and by market pressures. Moreover, for these efforts to be efficient and sustainable, the control engineering community will need to communicate their experiences via a host of new books, laboratories, simulations, and web-based resources. Thus, there will be a need for several different and complementary approaches. In this context, the authors believe that this book will have been successful if it contributes, in some way, to the revitalization of interest by students in the exciting discipline of control engineering. We stress that this is not a how-to book. On the contrary, we provide a comprehensive, yet condensed, presentation of rigorous control engineering. We employ, and thus require, mathematics as a means to model the process, analyze its properties under feedback, synthesize a controller with particular properties, and arrive at a design addressing the inherent trade-offs and constraints applicable to the problem. In particular, we believe that success in control projects depends on two key ingredients: (i) having a comprehensive understanding of the process itself, gained by studying the relevant physics, chemistry, and so on; and (ii) by having mastery of the fundamental concepts of signals, systems, and feedback. The first ingredient typically occupies more than fifty per cent of the effort. It is an inescapable component of the complete design cycle; however, it is impractical for us to give full details of the processes to which control might be applied, because they cover chemical plants, electromechanical systems, robots, power generators, and so on. We thus emphasize the fundamental control engineering aspects that are common to all applications and we leave readers to complement this emphasis with process knowledge relevant to their particular problem. Thus, the book is principally aimed at the second ingredient of control engineering. Of course, we do give details of several real-world examples, so as to put the methods into a proper context. The central theme of this book is continuous-time control; however we also treat digital control in detail, because most modern control systems will usually be implemented on some form of computer hardware. This approach inevitably led to a book of larger volume than originally intended, but one with the advantage of providing a comprehensive treatment within an integrated framework. Naturally, there remain specialized topics that are not covered in the book; however, we trust that we provide a sufficiently strong foundation so that the reader can comfortably turn to the study of appropriate complementary literature. Thus, in writing this book we chose as our principal goals the following:
Design is a complex process, one that requires judgment and iteration. The design problem normally is incompletely specified, sometimes is ill-defined, and many times is without solution. A key element in design is an understanding of those factors that limit the achievable performance. This naturally leads to a viewpoint of control design that takes account of these fundamental limitations. This viewpoint is a recurring theme throughout the book. Our objective is not to explore the full depth of mathematical completeness but instead to give enough detail so that a reader can begin applying the ideas as soon as possible. This approach is connected to our assumption that readers will have ready access to modern computational facilities, including the software package MATLAB-SIMULINK. This assumption allows us to put the emphasis on fundamental ideas rather than on the tools. Every chapter includes worked examples and problems for the reader. The book is divided into eight parts. A brief summary of each of the parts is given here: Part 1: The Elements Part II: SISO Control Essentials Part III: SISO Control Design Part IV: Digital Computer Control Part V: Advanced SISO Control Part VI: MIMO Control Essentials Part VII: MIMO Control Design Part VIII: Advanced MIMO Control Two of the authors (Goodwin and Salgado) have taught undergraduate and postgraduate courses of the type mentioned above, using draft versions of this book, in Australia and South America. The material in the book is illustrated by several industrial case studies with which the authors have had direct involvement. Most of these case studies were carried out, in collaboration with industry, by the Centre for Integrated Dynamics and Control (CIDAC) (a Commonwealth Special Research Centre) at the University of Newcastle. The projects that we have chosen to describe include the following:
Many of the case studies have also been repeated, and further embellished, on the book's web page, where Java applets are provided so that readers can experiment with the systems in the form of a ``virtual laboratory". A secondary advantage of having the case studies gathered in one place on the web page is that real control problems usually bring together many aspects, and thus it is difficult to localize them in the book. The web page thus gives a holistic view of the issues involved in the case studies. In addition, we refer to several laboratory-scale control problems, including a ball and plate mechanism, coupled tanks apparatus, and inverted pendulum. Each of these is the basis of a laboratory experiment within our universities to illustrate control principles. Alternatively see the authors' home pages for a link. Newcastle, Australia
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