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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
                 Copyright © 2020 Elsevier Ltd. All rights reserved.
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