Three phase induction motors employ a simple construction composed of a stator covered with 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 where a rotating electro-magnetic field it developed by applying 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 tries to follow stator’s magnetic field, pulling the rotor into rotation.
Benefits of AC Induction Motors are:
Induction motors are basic and rugged in building. They are better quality and can operate in virtually any environmental condition
Induction motors are cheaper in expense due to simple rotor construction, lack of brushes, commutators, and slide rings
They are maintenance free motors unlike dc motors because of the lack of brushes, commutators and slip rings
Induction motors could be operated in polluted and explosive conditions as they don’t have brushes that may cause sparks
AC Induction motors are Asynchronous Machines and therefore the rotor does not turn at the specific same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator quickness is necessary to be able to generate the induction in to the rotor. The difference between the two is named the slip. Slip should be kept within an optimal range in order for the motor to use efficiently. Roboteq AC Induction controllers can be configured to operate in another of three modes:
Scallar (or Volts per Hertz): an Open loop mode in which a control causes a simultaneous, fixed-ratio Frequency and Voltage alter.
Controlled Slip: a Shut Loop speed where voltage and frequency are managed to keep slip inside a narrow range while working at a preferred speed.
Field Oriented Control (Vector Drive): a Closed Loop Velocity and Torque control that functions by optimizing the rotating field of the stator vs. this of the induced field in the rotor.
See this video from Learning Engineering for a visual Induction Motor china illustration on how AC Induction Motors are constructed and work.