Control systems engineering, (second edition), I. J. Nagrath and M

Edition), 1. J . Nagrath and M. Gopal, 725 pp,
PBK, Wiley Eastern, 1982 Price: E7.50
The book is a typical introductory text on control
engineering, directed primarily at undergraduate
students and engineers. The authors have attempted to integrate topics from conventional and
modern control theory with interdisciplinary
readers in mind. This has been partially achieved
at the expense of depth and at times an incomplete presentation of the subject is given.
In Chapter I , a brief introduction is followed
by historical background and examples of typical
applications. Sampled data and multivariable
systems are mentioned while nothing is said about
the role of computers with regards to the development of control applications. Chapter 2 deals very
briefly with mathematical modelling of continuous time systems by differential equations. A
brief discussion for common physical systems is
followed by the introduction of the transfer function, signal flow graph and the block diagram.
The role and properties of feedback are discussed
in Chapter 3 where a brief account of sensitivity
analysis is also given. Chapter 4 really contains
complementary material to Chapter 2. Pointing
out the linearization about the operating point,
electrical components such as Servomotors,
Tachometer, Amplidyne and Stepper motors are
described. The remainder of Chapter 4 describes
hydraulic and pneumatic valves and pumps
followed by an insight into the operation of gyro
systems. Chapter 5 deals with time response
analysis in an unusual manner. Time domain
specification and simple performance indices are
defined and effects of 3-term control on the time
response is discussed hence optimum response is
defined. Concepts of BIB0 and asymptotic
stability are explained in Chapter 6 by using some
carefully chosen words and emphasizing the impulse response without mentioning convolution.
Mathematical arguments tend to be avoided. A
description of Routh-Hurwitz criterion concludes this chapter. Classical Root Locus and its
properties are presented in Chapter 7.
Chapters 8 and 9 deal with frequency response
analysis: basic definitions are followed by the
introduction of the Polar and Bode Plots.
Chapter 9 discusses Nyquist stability criteria, and
the concepts of gain and phase margin. M and N
circles are introduced and the Nichols Chart is
presented and used for gain adjustment. Chapter
10 gives a brief account of compensator design
using classical techniques such as Root Locus and
Bode diagrams. Chapter 1 I discusses sampled
data systems where basic principles are followed
by a brief account of stability analysis. The
extension of the classical design methods to
sampled data systems is however, given little
State space analysis is introduced in Chapter
12. The design techniques via state space are not
treated in any detail except for a brief account of
pole placement. At the end of this chapter the difference equation model of discrete systems and its
relation with z operator is presented. An
introduction to optimal control is given in
Chapter 13. Transfer function approach is first
discussed for both continuous and discrete
systems. The state variable approach is then used
to deal with regulator and tracking problems via
Pontryagin principles and dynamic programming
techniques. This chapter is concluded by formulating the Riccati equation for finite-time
regulator problems. Chapter 14 discusses the
nonlinear systems, again in much the same way as
other standard text books in this field. The
bang-bang type system is mentioned in the context of nonlinear systems rather than the optimality context, Lyapunov and Popov stability
methods are also presented in the chapter.
This book is on much of the same lines as the
books written by Ogata, Dorf and D’Azzo and
Houpis. Apart from the typographical errors, the
list of references given at the end of each chapter
is not sufficiently up to date to make the book
attractive to postgraduate and research students.
Several interesting examples are given at the
end of each chapter which are very suitable for
undergraduate tutorial and laboratory exercises.
Attempts have been made to stress the interdisciplinary nature of the subject and indeed the
book could be adopted for a wide range of
engineering courses.
On the whole the book is adequate for introducing the students and practical engineers to the
basic principles of control theory. It certainly
deserves a place on the shelf and is well worth
considering when selecting a text book for a first
course in control. The low price of the book is
also an added attraction.
Shiraz University
Shiraz, Iran