A permanent-magnet AC motor that operates at a rotor speed exactly synchronous with the supply frequency for precise speed control.
Full Definition
An elevator synchronous motor — almost universally of the permanent-magnet synchronous motor (PMSM) type in modern gearless traction machines — is an AC motor in which the rotor is fitted with high-energy NdFeB (neodymium-iron-boron) or ferrite permanent magnets that create a fixed magnetic field; the rotor locks in synchronism with the rotating stator magnetic field produced by the three-phase supply from the variable-frequency drive (VFD), resulting in rotor speed equal to supply frequency divided by pole pairs. PMSM gearless traction machines for elevators typically range from 2-pole to 24-pole designs, with rated outputs of 3–45 kW and rated speeds of 50–300 rpm. The high pole count allows the motor to develop full torque at low speed without a gearbox, dramatically reducing the machine envelope. Compared to induction motors, PMSMs offer 20–30 % higher efficiency (IE4 Super Premium class per IEC 60034-30-1), substantially lower thermal losses, quieter operation, and higher power density. The VFD performs field-oriented control (FOC) or direct torque control (DTC) of the PMSM using encoder feedback from the motor shaft for precise position and speed regulation essential for accurate floor levelling (±3 mm). The permanent magnets retain their field strength for the rated life of the motor (≥ 20 years at rated temperature) provided operating temperature does not exceed the magnet's specified coercivity threshold. After a magnet demagnetisation event (excessive current or temperature), the motor must be replaced rather than repaired.
