Three phase induction motors have a very 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 focus on the theory of induction in which a rotating electro-magnetic field it produced 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 creates 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 simple and rugged in construction. They are better quality and can operate in any environmental condition
Induction motors are cheaper in expense due to simple rotor construction, absence 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 conditions as they do not have brushes that may cause sparks
AC Induction motors are Asynchronous Machines meaning that the rotor will not turn at the precise same speed since the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is necessary to be able to create the induction in to the rotor. The difference between your two is called the slip. Slip must be kept in a optimal range in order for the motor to operate efficiently. Roboteq AC Induction controllers can be configured to operate in another of three modes:
Scallar (or Volts per Hertz): an Open up loop mode in which a order causes a simultaneous, fixed-ratio Frequency and Induction Motor voltage change.
Controlled Slip: a Closed Loop speed where voltage and frequency are managed to keep slip within a narrow range while operating at a preferred speed.
Field Oriented Control (Vector Drive): a Closed Loop Quickness 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.