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What is the difference between an AC induction and synchronous AC motor?

Motor and fan related questions

In both induction and synchronous motors, the AC power supplied to the motor stator windings create a magnetic field that rotates in time with the AC oscillations.

The rotor of a synchronous motor is equipped with permanent magnets. A PMSM (Permanent Magnet Synchronous Motor) uses permanent magnets embedded in the steel rotor to create a constant magnetic field. The stator carries windings produce a rotating magnetic field. At synchronous speed the rotor poles lock to the rotating magnetic field. These motors are not self-starting and therefore they need to be combined with a frequency inverter to be able to operate them.

The magnetic field in the rotor of an induction motor is created solely by induction instead of being self-magnetized as in permanent magnet motors. For rotor currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating magnetic field; otherwise the magnetic field would not be moving in relation to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as asynchronous motors.

For induction motors, following international efficiency standards have been defined: IE1, IE2, IE3, IE4 and IE5. Synchronous motors are often referred to as PMSM (Permanent Magnet Synchronous Motors), BLDC (Brushless DC) motors or SyncRM (Synchronous Reluctance Motors).
All these types of motors can be controlled via our frequency inverters.