Six Phase Permanent Magnet Machine with Fractional Slot Concentrated Winding

Permanent Magnet Machines (PMM) with a phase number (m) higher than three allow redundancy and lower torque ripple compared to their three phase counterparts. In this paper, a six phase permanent magnet machine with surface rotor magnets, designed with fractional slot tooth winding is proposed. A stator design with fractional slot tooth winding allows the design of a compact machine through shorter end winding and less copper volume. Fractional slot tooth windings cause additional space harmonics in the air gap which cause additional torque ripple and rotor losses (iron and magnet losses). The influence of the tooth winding (with single layer and double layer layout) and the influence of the higher number of phases on the torque ripple of a sinusoidal fed PM-machine are discussed. The paper includes winding design consideration for single and double layer winding layout. Criteria for feasible slot/pole combinations for the two winding variants are proposed. An analytical way to calculate the Magneto motive force (MMF), counting for the space harmonics in the air gap, is illustrated. With the MMF distribution in the air gap, the average torque and the current related torque ripple for the PMM with surface rotor magnets is calculated analytical. The analytically results are compared with a Finite element (FEM) calculation. Keywords—Multiphase, fractional slot winding, single layer, double layer, winding function, MMF distribution, torque ripple