Three phase induction motors employ a simple construction made up of a stator protected with electromagnets, and a rotor made up of conductors shorted at each end, arranged as a “squirrel cage”. They work on the principle of induction in which a rotating electro-magnetic field it developed through the use of a three-phase current at the stators electromagnets. Therefore 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 structure. They are more robust and can operate in any environmental condition
Induction motors are cheaper in cost due to simple rotor construction, absence of brushes, commutators, and slip rings
They are free of maintenance motors unlike dc motors due to the lack of brushes, commutators and slip rings
Induction motors can be operated in polluted and explosive conditions as they do not have brushes which can cause sparks
AC Induction motors are Asynchronous Machines meaning that the rotor will not turn at the specific same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator rate is necessary in order to make the induction into the rotor. The difference between the two is named the slip. Slip should be kept within an optimal range in order for the motor to operate effectively. Roboteq AC Induction controllers can be Induction Motor configured to operate in another 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 Closed Loop speed where voltage and frequency are controlled to keep slip within a narrow range while operating at a desired speed.
Field Oriented Control (Vector Drive): a Closed Loop Acceleration 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.