Glossary · Motion control and drives
Permanent-magnet synchronous motor (PMSM)
Also known as: PM synchronous motor, PMSM
German: Permanentmagnet-Synchronmotor (PMSM)
In electric drives, a permanent-magnet synchronous motor (PMSM) is an AC synchronous motor whose rotor field is produced by permanent magnets, so the rotor turns in step with the stator's rotating field. It is fed by a drive with sinusoidal currents.
- Motion control
In one sentence
A PMSM is an AC synchronous motor with permanent magnets in the rotor; it turns in step with the field and needs a drive.
Example
Most servo motors in packaging machines are PMSMs with integrated absolute encoders.
How it applies
- Engineering: PMSMs offer high efficiency and torque density. They need a drive with rotor position information, from an encoder or a sensorless method.
- Operation: When the rotor is turned from outside, for example by a falling load or during manual rotation, the motor generates voltage at its terminals even with the drive switched off.
- Maintenance: Handling magnets requires care; disassembling rotors is usually reserved for the manufacturer.
- Documentation: Warn in the maintenance instructions that motor terminals can carry dangerous voltage when the shaft turns, and describe how to prevent rotation before working on cables (Electrical hazard).
PMSM vs. induction motor
A PMSM runs synchronously and has no rotor losses from induced currents, so it is more efficient. An Induction motor can run directly on the grid and is cheaper, but has slip and lower torque density.