Induction (AC) Motors
Induction motors are the dominant type of motor used in alternating-current (AC) applications. They account for more than 90% of all installed horsepower, largely because they are rugged, simple, reliable, and cheap. They are so named because the power in the rotor is induced through moving magnetic fields in the stator.
Direct Current (DC) Motors
DC motors use direct current (DC) rather than AC. One type of DC motor—the electronically commutated motor (ECM)—is sometimes found in variable-speed HVAC applications, such as in fans and chiller compressors. They can be more efficient and easier to control than induction motors.
Synchronous motors are generally used for very large AC applications where more than 100 hp is required, and are rare in commercial facilities.