Three phase induction motors have a very simple construction made up of a stator covered with electromagnets, and a rotor composed of conductors shorted at each end, arranged as a "squirrel cage". They work on the theory of induction where a rotating electro-magnetic field it developed by applying a three-phase Induction Motor china current at the stators electromagnets. This in turn induces a current within the rotor's conductors, which in turns generates rotor’s magnetic field that attempts to follow stator’s magnetic field, pulling the rotor into rotation.
Great things about AC Induction Motors are:
Induction motors are simple and rugged in building. They are more robust and can operate in any environmental condition
Induction motors are cheaper in expense because of simple rotor construction, lack of brushes, commutators, and slide rings
They are free of maintenance motors unlike dc motors because of the lack of brushes, commutators and slip rings
Induction motors could be operated in polluted and explosive environments as they do not have brushes which can cause sparks
AC Induction motors are Asynchronous Devices and therefore the rotor will not switch at the exact same speed because the stator's rotating magnetic field. Some difference in the rotor and stator rate is necessary in order to make 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 effectively. Roboteq AC Induction controllers could be configured to operate in one of three modes:
Scallar (or Volts per Hertz): an Open up loop mode where 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 running at a preferred 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.
See this video from Learning Engineering for a visual illustration on how AC Induction Motors are constructed and function.