Three phase Induction Motor Induction motors employ a simple construction made up of a stator protected with electromagnets, and a rotor made up of conductors shorted at each end, arranged as a “squirrel cage”. They work on the theory of induction in which a rotating electro-magnetic field it developed through the use of a three-phase current at the stators electromagnets. This in turn induces a current in the rotor’s conductors, which in turns creates rotor’s magnetic field that tries to check out stator’s magnetic field, pulling the rotor into rotation.

Great things about AC Induction Motors are:

Induction motors are simple and rugged in structure. They are better quality and can operate in any environmental condition

Induction motors are cheaper in cost due to simple rotor construction, lack of brushes, commutators, and slip 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 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 acceleration is necessary in order to make the induction in to the rotor. The difference between the two is named the slip. Slip should be kept in a optimal range in order for the motor to operate efficiently. Roboteq AC Induction controllers could be configured to operate in another of three modes:

Scallar (or Volts per Hertz): an Open loop mode in which a command causes a simultaneous, fixed-ratio Frequency and Voltage alter.

Controlled Slip: a Closed Loop speed where voltage and frequency are managed to keep slip inside a narrow range while operating at a desired speed.

Field Oriented Control (Vector Drive): a Closed Loop Swiftness and Torque control that functions 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.