Three phase induction motors employ a simple construction made up of a stator covered with electromagnets, and a rotor made up of conductors shorted at each end, arranged as a “squirrel cage”. They focus on the basic principle of induction in which a Induction Motor rotating electro-magnetic field it made through the use of a three-phase current at the stators electromagnets. Therefore induces a current inside the rotor’s conductors, which in turns produces 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 basic and rugged in structure. 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 slide rings
They are maintenance free motors unlike dc motors due to the lack of brushes, commutators and slip rings
Induction motors can be operated in polluted and explosive environments as they do not have brushes that may cause sparks
AC Induction motors are Asynchronous Devices meaning that the rotor will not convert at the specific same speed as the stator’s rotating magnetic field. Some difference in the rotor and stator speed is necessary in order to create the induction into the rotor. The difference between the two is called the slip. Slip should be kept in a optimal range to ensure that the motor to operate 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 where a control causes a simultaneous, fixed-ratio Frequency and Voltage change.
Controlled Slip: a Closed Loop speed where voltage and frequency are managed to keep slip inside a narrow range while running at a desired speed.
Field Oriented Control (Vector Drive): a Closed Loop Speed and Torque control that works 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 function.