Reduction of Rotor Eddy-Current Losses for Surface PM Machines With Fractional Slot Concentrated Windings and Retaining Sleeve

High strength nonmagnetic metallic retaining sleeve is widely used in surface permanent magnet (SPM) machines for mechanical reliability, especially to high speed machines. Rotor eddy-current losses would be significantly increased in fractional slot concentrated winding (FSCW) SPM machines using sleeve. In this paper, the novel structure with copper damping rings inserted in rotor lamination is proposed. A current will be induced in the damping rings in reaction to the nonsynchronous harmonics field in the rotor, therefore, the eddy-current losses in sleeve and magnet will be reduced. FSCW SPM machines with common slot and pole combination such as 9-slot/8-pole, 12-slot/10-pole, and 24-slot/22-pole are investigated by the finite element analysis tools, and simulation results indicate that the eddy-current loss in sleeve, particularly on the single layer windings, is significantly reduced using the proposed structure.