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7
Induction motors
Chapter outline
7.1 Induction motor characteristics................................................................................................. 188
7.2 Scalar control............................................................................................................................... 193
7.3 Vector control.............................................................................................................................. 196
7.3.1 Vector control principles .................................................................................................. 198
7.3.2 Implementation of vector control................................................................................... 200
7.3.3 Vector control using sensors............................................................................................ 201
7.3.4 Sensorless vector control.................................................................................................. 203
7.4 Matrix converter ......................................................................................................................... 205
7.5 Summary...................................................................................................................................... 206
References........................................................................................................................................... 207
As noted in the introduction, this book is primarily concerned with motor-drives that are
capable of being used in a wide range of low-to medium-power closed-loop servo
applications. With the recent advances in microprocessor technology, it is now possible
to develop commercially viable drives that allow alternating-current (a.c.) asynchronous
induction motors to be controlled with the accuracy and the response times which are
necessary for servo applications. The importance of this development should not be
underemphasised. Induction motors are perhaps the most rugged and best-understood
motors presently available. Alternating-current asynchronous motors are considered to
be the universal machine of manufacturing industry. It has been estimated that they are
used in seventy to eighty per cent of all industrial drive applications, although the
majority are used in fixed-speed applications, for example pump or fan drives. The main
advantages of induction motors are their simple and rugged structure, their simple
maintenance, and their economy of operation. Compared with brushed motors,
a.c. motors can be designed to give substantially higher output ratings with lower
weights and lower inertias, and they do not have the problems which are associated with
the maintenance of commutators and brush gears. The purpose of this chapter is to
briefly review the operation of advanced induction-motor-drive systems which are
capable of matching the performance other servo motor-drives.
While induction motors are widely used in fixed-speed applications, variable-speed
applications are commonplace across industry. Therefore, as an introduction to
induction motors, this chapter will first briefly consider speed control using both
Electric Drives and Electromechanical Systems. https://doi.org/10.1016/B978-0-08-102884-1.00007-8 187
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