Reduction of Rotor Eddy Current Loss in High Speed PM Brushless Machines by Grooving Retaining Sleeve

Eddy currents might be significant in the rotor of a high speed permanent magnet brushless machine, especially when a metal retaining sleeve is applied. Various methods have been used to reduce the eddy currents. In this paper, a simple method, by grooving the retaining sleeve, is proposed, such that the flowing path of the eddy currents is obscured and the energy loss is thus suppressed. Circumferential, axial and comprehensive grooving are comparatively studied, particularly on the aspects of loss reduction, sleeve mechanical strength, rotor dynamic balance, and manufacture process complexity. It is proved that the circumferential grooving is the most effective for overall performance improvement and the simplest for practical manufacture with little extra cost.