Three phase induction motors have a very 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 basic principle of induction where a rotating electro-magnetic field it produced by applying a three-stage current at the stators electromagnets. This in turn induces a current inside 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 basic and rugged in structure. They are better quality and can operate in any environmental condition
Induction motors are cheaper in cost Induction Motor because of 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 can be operated in polluted and explosive conditions as they don’t have brushes that may cause sparks
AC Induction motors are Asynchronous Machines meaning that the rotor will not turn at the precise same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator rate is necessary to be able to create the induction into the rotor. The difference between the two is called the slip. Slip should be kept within an optimal range to ensure that the motor to operate effectively. Roboteq AC Induction controllers can 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 change.
Controlled Slip: a Closed Loop speed where voltage and frequency are controlled in order to keep slip within a narrow range while running at a preferred speed.
Field Oriented Control (Vector Drive): a Closed Loop Speed 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.