Three phase induction motors have a very simple construction made up of a stator protected with electromagnets, and a rotor composed 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 made by applying a three-stage current at the stators electromagnets. Therefore induces a current within the rotor’s conductors, which in turns Induction Motor produces 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 simple and rugged in structure. They are more robust and can operate in virtually any environmental condition
Induction motors are cheaper in expense because of 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 environments as they don’t have brushes that may cause sparks
AC Induction motors are Asynchronous Devices meaning that the rotor will not convert at the specific same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is necessary in order to generate the induction into the rotor. The difference between your two is called the slip. Slip must be kept within an optimal range to ensure that the motor to operate efficiently. Roboteq AC Induction controllers can be configured to operate in one of three modes:
Scallar (or Volts per Hertz): an Open loop mode where a order causes a simultaneous, fixed-ratio Frequency and Voltage change.
Controlled Slip: a Shut Loop speed where voltage and frequency are managed in order to keep slip within a narrow range while working at a desired speed.
Field Oriented Control (Vector Drive): a Closed Loop Rate and Torque control that functions by optimizing the rotating field of the stator vs. this of the induced field in the rotor.
Find this video from Learning Engineering for a visual illustration on how AC Induction Motors are constructed and function.