SPEED CONTROL OF THREE-PHASE IM BY V/F OPEN AND CLOSE LOOP METHOD

Abstract

This paper presents the simulation method to control the speed of three phase induction motor by v/f method. Simulation model for speed control in both open loop and close loop is shown here because these motors are the most widely used electrical motor due to the reliability, cheaper cost and thew. Out of the several methods of speed control of an induction such as change of number of poles, variation in frequency, variable stator voltage, constant V/f control, variable rotor resistance, slip recovery method etc., the closed loop constant V/f speed control method is most widely used. Pulse width modulated inverter is the basic requirement of the scheme. Here first a PWM Inverter is modeled and its outputs is fed to the Induction Motor drivesA MATLAB SIMULINK MODEL was designed to successfully implement Open Loop V/f Control on a PWM-Inverter fed three-phase Induction Motor, and the torque is observed to be constant for various rotor speeds. Then a MATLAB model for Closed-Loop V/f Control on a PWM-Inverter fed 3-phase Induction Motor. It was noticed that using a Closed-Loop scheme with a Proportional Integral gave a superior way of controlling the speed of an Induction motor.