A simple method for measuring cogging torque in permanent magnet machines

Cogging torque in permanent magnet machines causes torque and speed ripples, as well as acoustic noise and vibration. It is important to be able to accurately measure the cogging torque. This paper describes a simple test method for measuring the cogging torque waveform, together with finite element analyses. It is based on measuring the reaction torque on the stator and is suitable for both single-phase and three-phase PM machines, in which positive and negative cycles of the cogging torque waveform may be symmetrical or asymmetric.