A permanent magnet synchronous motor (PMSM) uses permanent magnetsembedded in the steel rotor to create a constant magnetic field. The stator carries windings connected to an AC supply to produce a rotating magnetic field. At synchronous speed the rotor poles lock to the rotating magnetic field. Permanent magnet synchronous motors are similar tobrushless DC motors.
Because of the constant magnetic field in the rotor these cannot use induction windings for starting. These motors require a variable-frequency power source to start.
The main difference between a permanent magnet synchronous motor and anasynchronous motoris the rotor. Some studies seem to indicate that NdFeB permanent magnet synchronous motors are around 2 percent more efficient than the highest-efficiency (IE3)asynchronous motors—using the same stator laminations and similar variable-frequency speed controllers.
Permanent magnet motors have been used as gearless elevator motors since 2000.