Control System Theory & Practice:دار جامعة عدن للطباعة والنشر تصدر كتاب بعنوان

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سلسلة الكتاب الجامعي لعام 2013

بعنوان: 

Control System Theory & Practice

Dr. A.Wali Hadi

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This Engineering, University of Aden. It is intended to serve as a text book for those who are oriented towards electrical or control engineering and for other specializations probably less involved in control. It is a standard fundamental text book in Control Systems, which also serves as a basis for other more advanced courses in control engineering. So, this is a standard course known under various titles such as: Automatic Control Systems, Feedback Control Systems or Theory of Linear-Cbook comes as the outgrowth of  teaching this course, for more than a decade,  the undergraduate students of Electrical Engineering Department, Faculty ofontinuous Systems etc. Control systems are in fact systems with feedback. Feedback control is the basic mechanism by which systems, whether mechanical, electrical or biological, maintain their equilibrium or homeostasis. But we are not concerned here with natural control systems, such as those that occur in living organisms or in society, but with man-made control systems such as those used to control automobiles, aircrafts, satellites, robots and industrial processes. Feedback control may be defined as the use of different signals, determined by comparing the actual values of system variables to their desired values, as a means of controlling a system. An everyday example of a feedback control system is an automobile speed control, which uses the difference between the actual and the desired speed to vary the fuel flow rate.

Due to the basic nature of this course, the studied systems are essentially linear and continuous. However, a sufficient introductory material is given for discrete-data or digital systems. The theoretical aspects of control systems are covered in detail and complemented by a wealth of examples, solved problems and exercises.

This text book is subdivided into ten chapters:

The first one serves as a general introduction in control engineering; it provides the historical background of control engineering and the basic concepts of classical control theory.

The classical topic of modelling dynamic systems with differential equations is given in chapter two. This is complemented by analyzing the system performance in the t-domain in Chapter three. Emphasis is made on the solution of differential equations by classical analytical methods and by numerical methods associated with computational aids.

Chapter four is devoted to the standard subject on transfer functions, block diagrams and signal flow graphs. This method finds wide application in practice for the analysis of control system in the s-domain, due to its simplicity, flexibility and acceptable accuracy. Moreover, in this chapter, the main aspects of evaluating the performance of control systems i.e. stability, accuracy and sensitivity are presented. It should be noted, at this level, that algebraic criteria of stability are given only. Further criteria and techniques are given in respective chapters essentially those based on frequency response and root locus technique. Therefore this chapter is considered the core chapter and constitutes the minimum knowledge that any involved student needs.

In chapter five, the frequency-response method of analysis is presented. The three approaches of constructing frequency-transfer functions are discussed in sufficient detail. These methods are: Bode diagrams, Nyquist plots and Nichols diagrams. In these methods, the magnitude and the phase of the frequency-transfer function are varied function of the frequency, however the approach in each plot differs from one method to another.

The last method of classical control i.e. root-locus technique is discussed in chapter six. This method generalizes the idea presented in differential equation analysis consisting in that the system output and performance depends upon the location of the roots of the characteristic equation of the system in the s-plane. Thus the loci of the roots of the system are plotted by varying the overall gain of the system from zero to infinity. The gain can be varied in the negative direction for the complementary root loci of the system. A wealth of numerical examples are given along with further exercises. By this, the main methods of classical control are covered. This material may be sufficient for students who are not specialized in control engineering.

More advanced material in control systems is given starting by chapter seven, in which the state-variable method of analysis of control systems is treated. It is well known that although this method is considered as a ‘modern method’, it is, strictly speaking, based on the transformation of higher-order differential equations into a set of first-order differential equations. However, this approach makes this method more adapted to multi-variable systems and computer solutions.

All the cited methods are related to the analysis of linear, time-invariant and continuous control systems. The other complementary aspect of study of control systems i.e. design of control systems is treated in chapter eight. This is precisely, the synthesis of analogue controllers: proportional (P), proportional-integral (PI), proportional-derivative (PD) and proportional-derivative-integral (PID). It is important  to underline that it is estimated around of 90% of controllers used in industry are PID controllers. The design of the other category of analogue controllers known as:: phase-lead, phase-lag and lead-lag compensators is also performed with the same depth of treatment. Frequency-response and root-locus methods are applied for the design of both categories of analogue controllers. These eight chapters cover both aspects of analysis and design of classical control or linear-continuous systems.

Chapter nine is concerned with another type of control systems i.e. Discrete-Data Control Systems or Digital Control Systems  in which computers, microprocessors and other digital devices are used for control of plants or processes. It should be recognized that the presented material is just an introduction to this extremely important area of control and for a full treatment normally a special book is required. However, the detail study of linear continuous systems or analogue systems serves as a good basis for the further study of digital control systems.

The last chapter in this book provides a brief outline of modern or advanced control to give sufficient insight at the main trends of their development, which is a valuable information for students wishing to deepen their knowledge in this area or probably for those who wish to continue their further study in control engineering..

The book is written by taking into consideration of the fulfilment the following tasks:

-  Limitation of the theoretical aspects to the required minimum, so some of the cited theorems are given without proof, but the interested reader can refer to respective references for more information on the topic.

-  Emphasis is given on problem solving and practical applications, therefore a big number of solved examples is given within each chapter.

-  The same level of importance is given for manual solution and computerized solution of tackled problems. It should be acknowledged here that the software Matlab is used for the solution of a wealth of examples and problems.

-  It is felt that is more appropriate to end each chapter by related problems for self study.

The book ends with appendixes including further material related to the treated topics, essentially: the respective tables of Laplace, z-transforms and modified z transform and w-transform are also given. Finally, a brief presentation of the utilized software in this book i.e. Matlab is presented.

The book is accompanied with a Solutions Manual of the questions and problems given at the end of chapter of the book. No doubt that this manual will offer further help for students as well as for instructors.

I hope that the collected material in this book will be helpful for our students in the Faculty and for students in other universities. Any comments or suggestions are always welcomed to my address or E-mail. Finally, I should acknowledge the help and support that I have found from my colleagues in electrical engineering department, interactivity and patience from my students and the Aden University Press that produces a good end of this book. A special gratitude is forwarded to

my family for their understanding and tolerance.