Three phase induction motors employ a 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 in which a rotating electro-magnetic field it developed by applying a three-phase current at the Induction Motor china stators electromagnets. This in turn induces a current inside 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 structure. They are better quality and can operate in virtually any environmental condition
Induction motors are cheaper in expense because of simple rotor construction, absence of brushes, commutators, and slip rings
They are maintenance free motors unlike dc motors due to the absence of brushes, commutators and slip rings
Induction motors could be operated in polluted and explosive conditions as they don't have brushes which can cause sparks
AC Induction motors are Asynchronous Machines meaning that the rotor will not switch 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 generate the induction in to the rotor. The difference between your two is called the slip. Slip must be kept within an optimal range in order for the motor to operate effectively. 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 control causes a simultaneous, fixed-ratio Frequency and Voltage alter.
Controlled Slip: a Closed Loop speed where voltage and frequency are controlled to keep slip within a narrow range while working at a preferred speed.
Field Oriented Control (Vector Drive): a Closed Loop Velocity and Torque control that works 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 work.