Permanent Magnet Motors (PM Motors)

A Permanent magnet motor is an AC motor that uses magnets imbedded into or attached to the surface of the motor’s rotor. The magnets are used to generate a constant motor flux instead of requiring the stator field to generate one by linking to the rotor, as is the case with an induction motor rotor and a squirrel cage motor’s rotor bars to maximize torque and efficiency.

A Permanent magnet motor can be divided into two main categories:

  1. Surface permanent magnet motors (SPM) and
  2. Interior permanent magnet motors (IPM)

SPM motors have the magnets affixed to the exterior of the rotor surface and in IPM motors magnet is assembled inside the rotor itself. SPM motors are suitable for low speed application. Unlike their SPM counterparts, the location of the permanent magnets make IPM motors very mechanically sound, and suitable for operating at very high speeds, an IPM motor has the ability to generate torque by taking advantage of both the magnetic and reluctance torque components of the motor. The IPM type having different slot design for improving torque & speed like double type, V type, Delta type etc.

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