Design and Simulation of a Three-Phase Induction Motor Speed Control System

Abstract

Three-phase Induction motors are increasingly used in a variety of applications such as fans, milling machines, transportation, etc. In applications requiring precise speed control such as robotics, centrifugal pumps, mills and other high-performance applications, it is essential that speed is maintained constant at a desired fixed value.  Many speed control techniques exist in literature but this paper presents the design of a simple PI controller and its use to control the speed of a three-phase induction motor. A controller design that applies the Phase margin (PM) as the stability criterion is employed. The cross-over frequency and phase margin of the open loop gain of motor and controller are specified in order to develop a stable control system. The three-phase induction motor model is presented and modified for the purpose of control. A comparative analysis between the motor performance with and without the PI controller was performed. The unit step response of the speed control loop is characterized by rise time, settling time, steady state error and peak overshoot of 0.0253s, 0.19s, 2.2e-14% and 24.03% respectively. Simulation results show that the speed of the uncontrolled motor changed whereas that of the controlled motor returned quickly to its initial value after the motor is subjected to load disturbances in steady state.