Different Types of Induction Motor Speed Control Methods


Induction motor speed control is very important in the industry. Three Phase Induction motors are one of the most commonly used motor type in electrical engineering industry. Since induction motors speed is constant it’s difficult to control the speed of this type of motor. In induction motors the speed controlling is also affected by the efficiency of this motor.  So there are different types of speed controlling method are used to control these induction motors. These speed controlling methods can mainly sub divide by considering the arrangement of the motor. Following are the may two type of controlling arrangement which need to consider by controlling Induction motors.

  • Induction motor speed control with respect to rotor side of the motor
  • Induction motor speed control with respect to stator side of the motor.
    Induction motor speed control with respect to stator side of the motor

    The speed control of induction motor by considering to control on stator side can also subdivide into several speed controlling methods such as.

    • By changing the supply voltage of the motor
    • Changing the stator pole numbers of the motor
    • Changing the frequency of the supply side of the motor

    By changing the supply voltage of the motor

    Torque product by the three-phase induction motor can show by the equation of shown below.

    So from this equation we can find out that

    So torque of induction motor indirectly proportional to the rotor side resistant. By adding external resistant into rotor can reduce the torque of the motor and increase its speed.
    Applying cascade connection

    in this cascade operation method of induction motor speed controlling there are two motors are mount on the same shaft of the motor and run at same speed.

    One motor is connected to three-phase supply and other is work from the feed induced emf of the first motor through slip rings.

    By using this method different speed can apply for induction motor and speed can control.  

    Injecting emf into rotor side circuit of the motor

    In this induction, motor speed control method external voltage add into the rotor circuit of the motor and the frequency must be same as slip frequency.

     So injecting emf in opposite phase of the rotor increase the rotor resistance. By that, this method can use to speed controlling of the induction motor.

    Hope that you can get some good understanding on the speed consorting methods applying in an induction motor.

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