f 2 (θ) be the modulation mmf wave.

P 1 be the number of poles of induction motor whose speed is to be controlled.

P 2 be the number of poles of modulation wave.

After modulation resultant mmf wave So we get, resultant mmf wave Therefore the resultant mmf wave will have two different number of poles Therefore by changing the number of poles we can easily change the speed of three phase induction motor.

- Adding external resistance on rotor side - In this method of speed control of three phase induction motor external resistance are added on rotor side. The equation of torque for three phase induction motor is
The three phase induction motor operates in low slip region. In low slip region term (sX) 2 becomes very very small as compared to R 2 . So, it can be neglected. and also E 2 is constant. So the equation of torque after simplification becomes,
The AC Induction motor is comprised of a simple cage-like rotor and a stator containing three windings. The changing field produced by the AC line current in the stator induces a current in the rotor which interacts with the field and causes the rotor to rotate. No brushes are necessary in this design. The base speed of the AC motor is determined by the number of poles built into the stator windings and the frequency of the AC input voltage . Variable speed control of an AC motor can be accomplished by increasing or decreasing the input frequency.

## Control induction motor pdf thesis vector

### Media: