4 CHAPTER 1. INTRODUCTION AND SCOPE OF THIS BOOK
Much of the task of designing a digital controller is in accounting for the effects of quantization
and sampling, especially sampling. If both T and q are small, digital signals approach continuous
signals, and continuous methods of analysis and design may be used. However, when this is not the
case, continuous methods can lead to erroneous results.
1.2 Philosophy and Text Coverage
The philosophy of this course is to present the basic material necessary for the analysis and design
of digital control systems. We assume a background in continuous systems, and relate the digital
problem to its continuous counterpart. The emphasis is on understanding the physical reality behind
the analysis.
The eight chapters in this book contain the following material:
Chapter 1. This chapter. Describes philosophy and content of book. Some definitions. Rationale
for studying digital control.
Chapter 2. Sampled (discrete-time) variables. Introduction of the z-transform for discrete vari-
ables, which is analogous to the Laplace transform for continuous variables.
Chapter 3. Discrete simulations of continuous systems. Several methods of simulation are given,
specifically numerical integration, pole-zero mapping, and zero-order hold equivalence.
Chapter 4. Frequency spectra of sampled signals. The impulse modulation model of sampling.
Aliasing and its effects.
Chapter 5. Transform-based design of digital control systems, primarily using the root locus
method. When sampling can be ignored, and when it must be considered.
Chapter 6. State-space modeling and analysis of continuous systems, including nonlinear systems.
Chapter 7. State-space design of digital control systems, primarily using pole placement. Control
law design and state estimation. Introduction of the reference input.
Chapter 8. System identification using the least squares method.
It is the author’s observation that digital control systems are so widely used that it is rare to see a
completely continuous control system. There are several reasons for this:
• Computers are getting faster, cheaper, and more reliable.
• Control systems incorporating computers are inherently more flexible than those without, e.g.
during the prototyping phase, tuning gains to achieve satisfactory performance is simply a
matter of changing numbers in a computer program, rather than changing hardware.
• Advanced control techniques such as optimal and adaptive control can only be realized digitally.