A type of AC synchronous motor using permanent magnets embedded in the rotor to generate the magnetic field, eliminating rotor copper losses and enabling the high-efficiency, compact gearless traction machines used in modern MRL elevators.
Full Definition
The Permanent Magnet Synchronous Motor (PMSM) has become the dominant traction machine technology in modern elevators since the late 1990s. Unlike induction motors that require rotor current for magnetisation, PMSM rotors use high-energy rare-earth permanent magnets (typically neodymium-iron-boron, NdFeB) that provide constant magnetic flux without electrical excitation. Key advantages: (1) High efficiency — elimination of rotor copper losses gives overall efficiencies of 90–95%, directly reducing energy consumption and ISO 25745 ratings; (2) High torque density — allows compact, flat disc-motor designs suitable for machine-room-less (MRL) installations; (3) Smooth low-speed operation — ideal for accurate VVVF-controlled levelling; (4) Low maintenance — no brushes or slip rings; (5) Low noise and heat generation. PMSM machines require a sophisticated vector-controlled (FOC — Field-Oriented Control) VVVF drive for optimal performance. The absence of self-excitation means that if the VVVF fails, the motor provides no braking torque — hence a robust electromagnetic brake is essential. PMSM traction machines are type-examined to EN 81-50 for use in elevators.
