Three phase Induction Motor china 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 work on the theory of induction where a rotating electro-magnetic field it produced through the use of a three-phase current at the stators electromagnets. Therefore induces a current in the rotor’s conductors, which in turns creates rotor’s magnetic field that tries to check out 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 because of simple rotor construction, lack of brushes, commutators, and slip 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 environments as they do not have brushes which can cause sparks
AC Induction motors are Asynchronous Machines and therefore the rotor will not switch at the exact same speed as the stator’s rotating magnetic field. Some difference in the rotor and stator speed is necessary in order to create the induction in to the rotor. The difference between your two is named the slip. Slip must be kept in a optimal range to ensure that 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 change.
Controlled Slip: a Closed Loop speed where voltage and frequency are managed in order to keep slip within a narrow range while running at a desired speed.
Field Oriented Control (Vector Drive): a Closed Loop Rate and Torque control that works 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 about how AC Induction Motors are constructed and function.