16

Basic Control Systems

16.1 Power Semiconductor-Controlled Drives

16.2 Feedback Control Systems

16.3 Digital Control Systems

16.4 Learning Objectives

16.5 Practical Application: A Case Study—Digital Process Control

Problems

Electric energy is widely used in practice, because of the ease with which the system and device

performance can be reliably controlled. One of the major areas of electrical engineering of interest

to all engineers is control and instrumentation. Instrumentation is integrated throughout the book in

sections on electric circuits, electronic analog and digital systems, energy systems, and information

systems. This final chapter serves to introduce a variety of methods by which the performance

of physical systems is controlled. By focusing on control aspects, the integration of many of the

concepts used in the preceding chapters is effected.

Systemsis a term used in many fields of study: economics, ecology, social and physical

sciences. The catchword is used to describe an assemblage of components, subsystems, and

interfaces arranged or existing in such a fashion as to perform a function or functions in order to

achieve a goal.Controlrefers to the function or purpose of the system we wish to discuss. Control

is almost always realized not by a single component, such as a transistor, resistor, or motor, but

by an entire system of components and interfaces.

Control systems influence our everyday lives just as much as some of the other areas of

electrical engineering. Examples abound in practice: household appliances, manufacturing and

processing plants, and navigational and guidance systems, in which concepts of the analysis

and design of control systems are utilized. A control system, in general, can be viewed as an

interconnection of components—electrical, mechanical, hydraulic, thermal, etc.—so as to obtain

a desired function in an efficient and accurate manner. The control engineer is concerned with

the control of industrial processes and systems. The concepts of control engineering are not

limited to any particular branch of engineering. Hence, a basic understanding of control theory

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