Three phase induction motors employ a simple construction composed of a stator covered with electromagnets, and a rotor composed of conductors shorted at each end, arranged as a “squirrel cage”. They work on the theory of induction in which a rotating electro-magnetic field it made by applying a three-phase current at the stators electromagnets. This in turn induces a current within 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 simple and rugged in construction. They are more robust and can operate in virtually 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 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 and therefore the rotor does not convert at the exact same speed since the stator’s rotating magnetic field. Some difference in the rotor and stator acceleration is necessary to be able to make the induction into the rotor. The difference between the two is named the slip. Slip should be kept in a optimal range in order for the motor to operate effectively. Roboteq AC Induction controllers could be configured to operate in one of three modes:
Scallar (or Volts per Hertz): an Open up 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 managed to keep slip inside a narrow range while operating at a desired speed.
Field Oriented Control (Induction Motor china 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.