Module 16. Digital Control

This module provides a tutorial overview of digital control system analysis and design. After studying this module, the reader should understand the following:

• Discrete and continuous controller performance is similar for short sample times

• The discrete equivalent to a continuous-system RHP zero is a zero outside the unit circle

• A discrete control system is stable if the poles of the discrete closed-loop characteristic equation are inside the unit circle

• The discrete IMC procedure factors zeros outside the unit circle and negative zeros inside the unit circle into the "bad stuff"

• A continuous process transfer function with no RHP zeros may have an equivalent discrete transfer function with a zero outside the unit circle, if the relative order (difference in denominator and numerator orders) is 3 or higher.

The major sections of this module are as follows:

M16.1 Background

M16.2 PID Controllers

M16.3 Stability Analysis for Digital Control Systems

M16.4 Performance of Digital Control Systems

M16.5 Discrete IMC

M16.6 Summary