Motor Control Applications - AC Induction Motor

Most motors are AC induction motors. In fact, more than 80% of all motors are AC induction motors. An AC induction motor can be single phase, poly-phase, brushed, or brushless. Unlike DC motors, they can reliably operate heavy workloads over one horsepower (750 watts) and three-phases are required for the largest motors. In an induction motor, the stator windings induce a current flow in the rotor, like a transformer (unlike a brushed DC commutator motor.)

The stator creates a rotating magnetic field that drags the rotor around. The first commercial motors ran on direct current (DC) because they performed better; the same motor run with alternating current was problematic due to changing magnetic fields. As you may know, DC current flows in only one direction whereas with AC current, the direction of current flow changes periodically. Until Nikola Tesla invented the AC induction motor around 1888, AC power was in competition with DC power for large scale adoption. Due in large part to the AC induction motor, AC came into standard use. An induction motor is similar to a rotating transformer because power is transferred to the rotor by electromagnetic induction. The AC induction motor, still in prevalent use today, is a design with high reliability, ruggedness, long life, and low maintenance.