Rotor End Losses in Multi-Phase 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 non-overlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power vs. speed range, and fault-tolerance. This paper focuses on eddy current losses in the rotor clamping rings. Losses in the non-magnetic shaft with the option of i) metallic, ii) nonmetallic, and iii) metallic with shielding laminations clamping rings are 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 3-phase 12slot/10pole design will be presented to confirm that the losses in the rotor clamping rings can be very significant in case of FSCW and should not be overlooked during the design phase.