V/F Speed Control Technique of Three Phase Induction Motor

Abstract: When we connect an induction motor directly to the main supply it can run only at its rated speed. However, many operations need variable speed applications. Also we felt that in many applications input power is directly proportional to the cube of motor speed. Today about 90% of all industrial motor applications use three phase induction motor because they are simple in design, easy to maintain and are less costly than other design. There are many induction motor control techniques in practice today, but the most popular control technique is by generating variable frequency supply, which has constant voltage to frequency ratio. This technique is popularly known as V/F speed control technique. The torque developed by the induction motor is directly proportional to the ratio of the applied voltage and the frequency of supply. By varying the voltage and the frequency, but keeping their ratio constant, the torque developed can be kept constant throughout the speed range. This is exactly what VF control tries to achieve.

Keywords: Speed control, variable frequency, three phase induction motor, PWM, IGBT, simulations.