Rotor End Losses in Multiphase Fractional-Slot Concentrated-Winding Permanent Magnet Synchronous Machines

Fractional-slot concentrated windings (FSCW) have been gaining a lot of interest in permanent magnet (PM) synchronous machines. This is due to the advantages they provide including shorter nonoverlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power versus speed range, and fault tolerance. This paper focuses on eddy-current losses in the rotor clamping rings. Additionally, the loss in the nonmagnetic shaft with the option of i) metallic, ii) nonmetallic, and iii) metallic with shielding laminations clamping rings is analyzed. The study is based on finite element analysis (FEA). Desirable slot/pole combinations for different number of phases with both single- and double-layer windings are investigated. Experimental results for a three-phase 12 slot/10 pole design are presented to confirm that the losses in the rotor clamping rings can be very significant in case of FSCW machines and should not be overlooked during the design phase.