Chapter 10 - Digital Control Systems

The intent of this chapter is to provide the theoretical background and practical tools for
the design of a control system which is to be implemented with a computer or microprocessor.
The methods to be studied are primarily for closed-loop (feedback) systems in
which the dynamic response of the process being controlled is a major consideration in
the design. The design methods are applicable to any type of computer (from microprocessors
to large-scale computers); however, the effects of small word size and slow
sample rates take on a more important role when microprocessors are used.

It will be assumed in the chapter that the reader has some knowledge of controlsystem
design methods for continuous (or analog) systems such as those covered in
Chap. 13 and Refs. 1 and 2. Furthermore, a more complete reference for the subject
material of this chapter can be found in a digital control textbook like Ref. 3.

A typical topology of the type of system to be considered is shown in Fig. 10.1.
There are two fundamentally different methods for the design of digital algorithms:

1. Continuous design and digitization: Perform a continuous design, then digitize the
   resulting compensation.
2. Direct digital design: Digitize the plant model, then perform a design using discrete
   analysis methods.

Both methods will be covered and their advantages and disadvantages discussed.