Three phase induction motors have a very simple construction composed of a stator protected 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 in which a rotating electro-magnetic field it developed through the use of a three-stage 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 check out 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 better quality and can operate in any environmental condition

Induction motors are cheaper in cost because of simple rotor construction, lack of brushes, commutators, and slip rings

They are free of maintenance motors unlike dc motors because of the lack of brushes, commutators and slip rings

Induction motors can be operated in polluted and explosive conditions as they don’t have Induction Motor brushes that may cause sparks

AC Induction motors are Asynchronous Devices meaning that the rotor does not change at the exact same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator speed is necessary in order to develop 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 can be configured to operate in one of three modes:

Scallar (or Volts per Hertz): an Open loop mode in which a order causes a simultaneous, fixed-ratio Frequency and Voltage alter.

Controlled Slip: a Closed Loop speed where voltage and frequency are controlled to keep slip inside a narrow range while operating 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.