A preliminary survey of induction motor speed-control

Abstract

Spreading of the automation in the industry and transport calls for an increasing number of variable-speed drives. With the appearance of thyristor, the semi-conductor-controlled rectifier, design of variable-speed drives using induction motors became possible, and the interest for this type of drive has been growing in recent years among the research workers and the manufacturers of electrical equipment.

The present work is an attempt at synthesizing the information available on the subject and at advancing the understanding of some related problems. These can be separated into three groups: steady-state and transient behaviour of induction motor on the variable-frequency supplies, closed-loop control of speed and torque, and design of variable-frequency supplies (thyristor invertors).

Methods of analysis of induction motor behaviour including the analog modelling and digital computation of the parameters determining its transient properties are described, and approximate models are developed.

Experimental speed-control system is described, whose design relies on the information on the motor behaviour. Closed-loop control of motor speed from zero to rated speed, reversal of rotor speed and indirect limiting of the motor torque to a value below the pullout are the main aspects covered.

Basic problems of the commutation of thyristors in inverter circuits are outlined, and the operation and design of simple series type of invertor is discussed in detail, followed by the discussion of controlled rectifier circuits used as a link between the standard mains and the invertors. Details of the operation of auxiliary electronic circuits are given in the Appendixes

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