Three phase induction motors have a very 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 basic principle of induction in which a rotating electro-magnetic field it created through the use of a three-stage current at the stators electromagnets. Therefore induces a current inside 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 basic and rugged in structure. They are more robust and can operate in any environmental condition
Induction motors are cheaper in cost 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 can be operated in polluted and explosive conditions as they don’t have brushes which can cause sparks
AC Induction motors are Asynchronous Machines and therefore the rotor does not switch at the exact same speed since the stator’s rotating magnetic field. Some difference in the rotor and stator speed is necessary to be able to create the induction into the rotor. The difference between the two is called the slip. Slip must be kept in a 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 where a control causes a simultaneous, fixed-ratio Frequency and Voltage modify.
Induction in Motor Controlled Slip: a Shut Loop speed where voltage and frequency are controlled in order to keep slip inside a narrow range while working at a desired speed.
Field Oriented Control (Vector Drive): a Closed Loop Rate 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 about how AC Induction Motors are constructed and work.