Three phase induction motors employ a simple construction composed 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 principle of induction in which a rotating electro-magnetic field it developed through the use of a three-phase 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 follow 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 cost because of simple rotor construction, absence of brushes, commutators, and slide rings
They are free of maintenance motors unlike dc motors because of the lack of brushes, Induction Motor china commutators and slip rings
Induction motors could be operated in polluted and explosive environments as they do not have brushes which can cause sparks
AC Induction motors are Asynchronous Machines 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 velocity is necessary in order to develop the induction in to the rotor. The difference between the two is called the slip. Slip must be kept within an optimal range to ensure that the motor to use effectively. Roboteq AC Induction controllers can be configured to operate in one of three modes:
Scallar (or Volts per Hertz): an Open loop mode where a command causes a simultaneous, fixed-ratio Frequency and Voltage alter.
Controlled Slip: a Shut Loop speed where voltage and frequency are managed in order to keep slip inside a narrow range while operating at a preferred 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.
Find this video from Learning Engineering for a visual illustration on how AC Induction Motors are constructed and function.