Three phase Induction in Motor induction motors employ a simple construction made up of a stator covered with electromagnets, and a rotor composed of conductors shorted at each end, arranged as a “squirrel cage”. They focus on the principle of induction where a rotating electro-magnetic field it made by applying a three-phase 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 attempts 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 construction. They are better quality and can operate in 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 conditions as they do not have brushes that may cause sparks
AC Induction motors are Asynchronous Devices and therefore the rotor will not convert at the exact same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator acceleration is necessary to be able to develop the induction in to the rotor. The difference between the two is named the slip. Slip must be kept in a 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 control causes a simultaneous, fixed-ratio Frequency and Voltage change.
Controlled Slip: a Shut 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 Velocity 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.