There are two books reviewed in this issue. The first book, Linear Systems, is a valuable contribution to the library of literature on linear systems. According to the reviewer, this book can be very useful in graduate courses on linear systems. The second book, Intelligent Automatic Generation Control, is a book the reviewer recommends for postgraduate students and researchers.
Henri Bourlès, Wiley, 2010, ISBN-13: 978-1848211629.
The literature on analysis and control of linear dynamic systems is vast. However, the book Linear Systems by Prof. Henri Bourlès still provides a valuable contribution to it. Bourlès currently holds the chair in automatic control at Conservatoire des Arts et Metiers (CNAM) in Paris, France. Among his broad teaching and research experience, Bourlès is well known by his contributions to power system control and more specifically to the problem of automatic voltage regulation (primary and secondary) through his collaboration both as employee and consultant of Electricité de France (EDF). The value of Bourlès's contribution comes from his approach to the mathematical formalization of the analysis and control problems of linear systems. He relays very much on what we can call the “French School of Automatic Control.” Together with classical methods, the book includes novel concepts and tools taken for the research literature.
Although Bourlès suggests that his book can be used for both undergraduate and graduate courses, I believe that it would be more appropriate for graduate students that have had previous exposure to control systems through a standard basic course. The writing style makes intensive use of the definition, theorem–proof, and remark elements that graduate students would find easier to follow. I agree with the author that two graduate courses can be built up from each of the two main parts of the book.
The book starts, as do many books on control systems, with a review of mathematical models of physical systems. Electric, mechanical, electromechanica,l and thermal-hydraulic systems are briefly reviewed.
The first part of the book comprises Chapters 2–6. Chapter 2 presents the basic concepts of the transfer function representation of linear dynamic systems. Chapter 3 discusses open-loop systems. Time response, frequency response, and other properties of first order, second order, and higher order together with time-delay systems are detailed. Chapter 4 addresses closed-loop systems. Stability, robustness, and performance properties are provided in detail. The robustness analysis is very detailed and very unusual in control system textbooks. Chapter 5 is devoted to the design of PD, PI, and PID controllers. Although the PD regulator and the lead compensation are discussed together, the design of the lag compensation is omitted when the PI controller is introduced. The first part of the book concludes with Chapter 6, which is devoted to the design of an RST controller. A controller of RST form is proposed to overcome the limitations of PID controllers. This form is classic but the pole placement method proposed to manage the performance/robustness tradeoff improves the methods previously proposed in the literature.
Chapters 7–11 make up the second part of the book. Chapters 7–9 are devoted to analysis and control of linear systems described in state-space form. Chapters 10 and 11 provide an introduction to discrete-time control systems and identification. The author has recognized the importance of these topics but admitted implicitly that a more detailed presentation of them was out of the scope of the book.
Chapter 7 presents the basic concepts of state-space systems. Chapter 8 presents the state feedback approach of a linear system. Two cases are considered separately: elementary state feedback and state feedback with integral action. The problem of state feedback with integral action is barely found in textbooks despite its practical relevance. Chapter 9 introduces the notion of observer. Moreover, observers for elementary state feedback and for state feedback with integral action control systems are developed. The robustness of the resulting control law is also analyzed.
Chapter 10 is devoted to discrete-time control. Discrete signals are introduced first. Then discrete systems in transfer form and state-space form are detailed. The chapter concludes with the synthesis of discrete control systems. Using the concept of “pseudocontinuous system,” this synthesis is completely analogous to that of a continuous control system. Chapter 11 introduces the problem of system identification. Random signals are reviewed first. Identification of both open- and closed-loop systems is presented subsequently.
Chapters 12 and 13 are, respectively, Appendices 1 and 2, which contain the mathematical foundations (calculus and linear algebra concepts and tools) of the book. These appendices do not merely remind the reader what he/she is supposed to know. They provide in detail the key concepts and tools needed to understand the book. Their importance in the book is confirmed by the fact that they take almost one third of the book.
Each chapter contains a set of exercises. Two types of exercises are proposed: theoretical and practical ones. “Theoretical exercises” require the reader either to prove a statement or to derive an equation. In “practical exercises,” the reader is asked to address an analysis and design problem in the same way that an engineer would do. Chapter 14 provides the solutions to the exercises. Moreover, MATLAB script files that contain the solutions of the exercises are available from the Web. Solutions to some exercises are also provided in the form of SCILAB script files. SCILAB is a novel tool worth knowing. Dealing with such script files could be a great occasion to learn about SCILAB.
I have found that this book can be very useful to build two graduate courses on linear systems. Analysis and control aspects are well balanced. Moreover, it can be of great value for practitioners looking for a mathematically sound formulation of the methods and tools they are using.
Reviewed by Luis Rouco
Intelligent Automatic Generation Control
Edited by H. Bevrani and T. Hiyama, CRC Press 2011
Automatic generation control (AGC) is one of the key control functions in modern power systems. AGC is one of the critical control functions in regulating the bulk power system frequency and also serves to control tie-line power flow over major boundaries between neighboring systems. With the advent of renewable generation technologies, the majority of which are of variable nature in their power output (e.g., varying wind and solar resource), AGC design and functionality has become of even greater importance. This book, Intelligent Automatic Generation Control, is a welcome text on this important subject in the context of these present changes in the industry.
The book starts with a brief chapter summarizing some of the actual implementations of intelligent control systems in the Japanese power system. Although brief, I found this chapter useful in presenting some clear examples of actual intelligent systems in operation in a power system. One important observation is that the majority of these intelligent systems are applied either offline or as a tool to guide planners and system operators, for example for determining unit commitment, load forecasting, or system restoration plans. Intelligent systems tend to be very effective in these applications where the combination and permutation of possibilities, or the inherent patterns of events, are quite complex and insurmountable to handle by traditional approaches. Thus, many intelligent system approaches such as rule-based systems or neural network applications can help to quickly identify patterns (e.g., in load behavior) and to provide invaluable guidance to planners and operators.
In general, there are still few applications of intelligent control systems that are applied to online systems, particularly at the local level (e.g., power plant controls). One of the major reason for this, which is actually alluded to in the book in a later chapter, is that intelligent control systems do not readily allow for an in-depth stability analysis of the resulting system. This can be a significant disadvantage particularly when dealing with control systems at the equipment level. This and many other aspects of intelligent systems are clearly ripe areas of further research.
Chapter 2 is a nice summary and introduction to the concept of AGC, how AGC is presently achieved, and what the goals and purpose of AGC are in a modern power system. There are a few minor errors in the chapter, but nothing too drastic. Some of these are with regards to industry organizations such as references to the North American Reliability Council, which is now the North American Reliability Corporation, and references to the Union for the Coordination of the Transmission of Electricity, which was reorganized into the European Network of Transmission System Operators for Electricity (ENTSOE). These are not major issues, plus one can hardly expect anyone to keep up with the ever-changing names of utilities and reliability entities!
Chapter 3 is essentially a literature review of research done in the application of intelligent control systems to the problem of AGC. Chapter 4 provides an overview of the restructuring of modern power systems into the deregulated frame work, namely, separate generation and transmission entities, and how this has affected the AGC problem. The chapter covers the effect of markets and market design on the AGC problem and presents a novel approach for modeling the market influences in the AGC control problem. This chapter perhaps makes one of the more compelling cases in the book for the need to consider intelligent control systems in the application of AGC. The chapter shows the added complexity that markets introduce to the problem of AGC, which is even further complicated by variable generation (e.g., renewables) and distributed generation.
Although the book does touch on the issue of variable generation technologies and how they affect system frequency and may even play a role in controlling it, this is covered only very briefly in a few parts of the book. Also, some of the discussion on this subject needs further explanation to avoid potential misinterpretation by the reader. A consideration for future editions may be to further develop the discussions around the impact of renewable technologies on system frequency control and AGC design.
Chapters 6–11 are detailed examples of the application of various intelligent control systems to the AGC problem, such as neural-networks, multiagent systems, fuzzy-logic control and so on. These chapters are interesting and certainly of value to post-graduate students and researchers who are interested in further research into the application of intelligent control to power systems. The final chapter of the book illustrates a simple example of an AGC system for small isolated systems.
In summary, I enjoyed reading the book and found it informative. It is certainly a book I would recommend to post-graduate students and researchers in the area of intelligent control systems and their application to power system control. My congratulations to the authors.
Reviewed by Pouyan Pourbeik