Three phase induction motors employ a simple construction composed of a stator protected with Induction Motor electromagnets, and a rotor made up of conductors shorted at each end, arranged as a “squirrel cage”. They focus on the basic principle of induction in which a rotating electro-magnetic field it produced through the use of a three-phase current at the stators electromagnets. This in turn induces a current in the rotor’s conductors, which in turns creates rotor’s magnetic field that attempts to follow stator’s magnetic field, pulling the rotor into rotation.
Benefits of AC Induction Motors are:
Induction motors are simple and rugged in construction. They are more robust and can operate in any environmental condition
Induction motors are cheaper in expense due to simple rotor construction, lack of brushes, commutators, and slide rings
They are free of maintenance motors unlike dc motors due to the absence of brushes, commutators and slip rings
Induction motors can be operated in polluted and explosive environments as they don’t have brushes that may cause sparks
AC Induction motors are Asynchronous Devices and therefore the rotor does not turn at the precise same speed as the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is necessary to be able to make the induction into the rotor. The difference between the two is called the slip. Slip should be kept within an optimal range to ensure that the motor to use efficiently. Roboteq AC Induction controllers could be configured to operate in one of three modes:
Scallar (or Volts per Hertz): an Open loop mode where a control causes a simultaneous, fixed-ratio Frequency and Voltage change.
Controlled Slip: a Closed Loop speed where voltage and frequency are controlled to keep slip inside a narrow range while working at a desired speed.
Field Oriented Control (Vector Drive): a Closed Loop Quickness and Torque control that functions by optimizing the rotating field of the stator vs. this of the induced field in the rotor.
Discover this video from Learning Engineering for a visual illustration about how AC Induction Motors are constructed and work.