Advanced Modern Control System Theory and Design

4

DIGITAL CONTROL-SYSTEM ANALYSIS AND DESIGN

4.1. INTRODUCTION

This chapter is concerned with a class of feedback control systems in which the signal at one or more points appears as a train of pulses rather than as a continuous function. Such a system is known as a digital control system, in contrast to a continuous control system, where the signal is continuous everywhere. The controlling information, determined by the amplitude of the pulses, is present only at discrete instants of time, which in this chapter, are assumed to be equally spaced. Because of the inherent time delay introduced by the sampling operation, stabilization of the digital control system becomes a more complex problem than with continuous systems requiring special techniques for analysis and design.

Digital control systems are used in a wide variety of applications. The impetus for the use of this class of control systems has been the ready availability of digital computers, and the improvement in cost and reliability of digital computers. Digital control systems are very common today and are used in controlling robots [1], navigation systems for aircraft and ships, aircraft autopilots, mass transit vehicles, chemical process control systems, and automation systems for various applications.

There are several excellent books avail able on digital control systems that are dedicated to this subject only [2–5]. The purpose of this chapter is to present digital control systems to the student and the practicing ...