Analysis of motor loss in permanent magnet brushless motors

This paper presents an analysis of the stator iron loss and the rotor eddy-current loss in 22-pole/24-slot modular and 24-pole/36-slot conventional permanent magnet brushless motors. The loss is evaluated by performing time-stepped finite element analysis. The no-load loss at 6 000 rpm is mainly due to the stator iron loss, while at rated load the eddy-current loss which is induced in the magnets is a major component of the total motor loss. It is shown that the no-load idling loss in the modular motor is lower than that of the conventional motor because it has fewer poles. On the other hand, the rotor eddy-current loss in the modular motor is higher because the stator armature magneto-motive force has lots order spatial harmonic components. It is also shown that the idling loss in the stator can be reduced by ∼50% by using 0.20 mm thick laminations rather than 0.35 mm laminations, whilst the eddy-current loss can be reduced significantly by segmenting the magnets circumferentially.

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