In this paper, we investigate the Eddy current (EC) losses in the rotors of surface permanent-magnet (PM) synchronous machines, which have concentrated armature windings. By the finite-element method (FEM) analysis, it is clear that the EC losses in rotors are apparently different at rated currents if the pole and slot combinations are different. The distribution of the EC density in the rotor is closely related with the asynchronous components of the armature magnetomotive force (MMF). If the armature MMF has a low order of spatial harmonic components, which is not synchronous with the rotor, the EC losses are of large amounts.Index Terms-Eddy current (EC), loss, magnetomotive force (MMF), rotor, surface permanent-magnet synchronous machine.

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A b s t r a c t -The paper studied the performance characteristics of a 3-phase cage induction motor using 3-D finite element technique. Especially, the effects of rotor skew and the rotor end-rings and the distribution of the electro-magnetic field toward the axial direction, which have not been able to be analyzed accurately by 2-D analysis, were investigated. Since the 3-D analysis enabled 11s to analyze the continuity of the air gap flux density a t t h e core ends a n d t o take into consideration the rotor end-ring impedance, the motor parameters were calculated with high accuracy, compared with 2-D analysis. Firstly, we made the relation of the rotor end-ring current with the rotor b a r current clear, by analyzing the harmonics of the rotor bar current and the rotor end-ring current in the cases of motors without rotor skew and with rotor skew. Secondly, the torque and the rotor axial force were calculated from the distribution of the electro-magnetic field obtained by the 3-D analysis in the case of rotor skew. We also calculated the axial forces on the both end-rings in the case of rotor skew. The results obtained i n t h e p a p e r showed t h e importance of 3-D analysis for the design of the induction motors.

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