Improvement of Three Phase Induction Motor Performance Using Voltage and Frequency Speed Control Techniques

Abstract

Inductions motors are the most commonly used electric motors because of their robustness, durability, reliability and low cost, and essentially lack the ability to run at variable speed operation. However, the first DC motors were applied to most of electric drives. The advent of power electronics has drastically made a lot of improvement, where alternating current drive is used to control and run the performance of induction motor. This research work presents the use of voltage and Frequency control technique to improve the performance of speed control of three phase 4-pole induction motor. Controlling the speed of motor using traditional method such as controlling the supply voltage ,changing the stator pole and others incurs running motor at full speed, speed instability, and the efficiency of the motor drop when motor speed is varied but the voltage and frequency ratio method of speed control solves this problem .A model and simulation in MATLAB for various method of speed control was analysed with constant voltage and frequency method showing much improvement on electromagnetic torque and the speed characteristic of the induction motor compared to other method such as change in stator  resistance, rotor resistance, number of poles, stator leakage resistance and others. Varying the line frequency at a maintained constant 8V/Hz V/F ratio and the effect of the torque-speed characteristics performance of the three phase 4-pole induction motor for line frequencies were investigated: (40Hz, 50Hz, 60Hz, 70Hz, and 80Hz). The result shows that as the line frequency increases, the torque decreases and the speed increases (or slip decreases), and for a line frequency of 40Hz, the torque observed is 43.6Nm while the rotor speed is 1076rpm. But for a line frequency of 80Hz, the peak torque was observed at 22Nm while the corresponding rotor speed was 2152rpm, thereby improving the speed control performances of the three phase 4-pole induction motor and its voltage frequency characteristics.