Influence on Rotor Eddy-Current Loss in High-Speed PM BLDC Motors

Rotor eddy-current loss appears significant in high-speed PM BLDC motors. It is mainly caused by three factors, viz., armature mmf time harmonics, armature mmf space harmonics, and airgap permeance variation due to slot openings. The latter two factors are determined by motor design. Particularly, they are related to the stator structure and the slot opening width, which will be investigated in this paper. Moreover, in order to improve the mechanical strength, the rotor is usually protected with a non-magnetic retaining sleeve, which also influences the rotor eddy-current loss, hence, will be inspected as well. Finally, a conductive shield between the retaining sleeve and magnets is proposed to reduce the rotor loss