Six Phase Fractional Slot Surface Permanent Magnet Motor for High Torque Density and High Speed

Multiphase electrical machines offer several advantages with respect to their three-phase counterparts, such as fault tolerance capability, mitigated harmonic spectrum and related lower torque ripple and rotor losses, reduced peak current rating. These advantages can vary significantly depending on the slot/pole combination and the application specifications. This paper focuses on rotor loss mitigation obtainable with the particular stator slot number (Q) and pole (2p) combination 2p = Q ± 2 for Double-Layer Fractional-Slot Surface Permanent Magnet machines. The direct comparison between three- and six-phase solutions is proposed with reference to traction application, with preliminary experimental validation. The paper demonstrates the convenience of the 6-phase solution, where the decrease of rotor loss leverages into a substantial improvement of the rotor operating temperature and ultimately of the continuous output power.