I. Introduction
The fractional slot concentrated winding (FSCW) surface permanent magnet (SPM) machines are widely used in many applications for its superior merits, such as high torque density, high efficiency, low torque ripple, and hence forth. The nonmagnetic metallic retaining sleeve is frequently used in high speed SPM machines for mechanical reliability [1]. However, the rotor eddy-current losses is a key disadvantages in FSCW SPM machines due to its rich harmonic contents of the stator magnetomotive force (MMF) [2], especially for high speed machines with metallic retaining sleeve.