Three phase induction motors employ a simple construction composed 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 in which a rotating electro-magnetic field it created through the use of a three-phase current at the stators electromagnets. Therefore induces a current inside the rotor’s conductors, which in turns produces rotor’s magnetic field that tries to follow stator’s magnetic field, pulling the rotor into rotation.
Great things about AC Induction Motors are:
Induction motors are basic 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, absence of brushes, commutators, and slip rings
They are free of maintenance motors unlike dc motors due to the absence 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 and therefore the rotor will not switch at the specific same speed since the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is Induction Motor necessary to be able to make the induction into the rotor. The difference between your two is named the slip. Slip should be kept within an optimal range to ensure that the motor to operate efficiently. Roboteq AC Induction controllers could be configured to operate in another of three modes:
Scallar (or Volts per Hertz): an Open loop mode in which a order causes a simultaneous, fixed-ratio Frequency and Voltage change.
Controlled Slip: a Closed Loop speed where voltage and frequency are managed to keep slip inside 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.
See this video from Learning Engineering for a visual illustration about how AC Induction Motors are constructed and work.