Three phase induction motors employ a simple construction made up of a stator protected with electromagnets, and a rotor composed of conductors shorted at each end, arranged as a “squirrel cage”. They work on the theory of induction where a rotating electro-magnetic field it developed by applying a three-stage current at the stators electromagnets. This in turn induces a current inside the rotor’s conductors, which in turns generates rotor’s magnetic field that attempts to check out stator’s magnetic field, pulling the rotor into rotation.
Benefits of AC Induction Motors are:
Induction motors are simple and rugged in construction. They are more robust and can operate in any environmental condition
Induction motors are cheaper in expense because of simple rotor construction, lack of brushes, commutators, and slip rings
They are maintenance free motors unlike dc motors because of the absence of brushes, commutators and slip rings
Induction motors can be operated in polluted and explosive environments as they do not have brushes which can cause sparks
AC Induction motors are Asynchronous Machines and therefore the rotor does not change at the exact same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is necessary in order to produce the induction in to the rotor. The difference between the two is called the slip. Slip should be kept in a optimal range in order for the motor to use effectively. Roboteq AC Induction controllers can be configured to operate in another of three modes:
Scallar (or Volts per Hertz): an Open loop mode in which a order causes a simultaneous, fixed-ratio Induction Motor Frequency and Voltage modify.
Controlled Slip: a Closed Loop speed where voltage and frequency are controlled in order to keep slip within a narrow range while operating at a preferred speed.
Field Oriented Control (Vector Drive): a Closed Loop Velocity 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 function.