Three phase induction motors have a very 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 principle of induction where a rotating electro-magnetic field it created by applying a three-stage current at the stators electromagnets. Therefore induces a current in 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 virtually any environmental condition
Induction motors are cheaper in expense because of simple rotor construction, absence 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 don’t have brushes which can cause sparks
AC Induction motors are Asynchronous Machines meaning that the rotor will not change at the specific same speed since the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is necessary to be able to produce the induction in to the rotor. The difference between the two is named the slip. Slip must be kept within an optimal range in order for the motor to operate Induction in Motor efficiently. 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 control causes a simultaneous, fixed-ratio Frequency and Voltage alter.
Controlled Slip: a Closed Loop speed where voltage and frequency are controlled to keep slip inside a narrow range while working at a desired 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.
Discover this video from Learning Engineering for a visual illustration on how AC Induction Motors are constructed and function.