Design issues of a fractional-slot windings axial flux PM machine with soft magnetic compound

The paper addresses some design aspects of a fractional-slot windings axial flux PM synchronous machine whose stator is made with soft magnetic composite. Since Axial Flux PM Synchronous machines have an inner stator hole, the number of stator slots is bounded, therefore in order to increase the number of poles per slots fractional slot windings arrangements can be utilized. Frequently, this procedure results into a more compact winding design, resulting in lower copper losses due to shorter end connections. The soft material used for the stator presents low eddy-currents losses at high frequency, and a self-cooling air channel system is provided. On the other hand, rotor peak temperatures rise more than expected due to rotor eddy currents. In fact, stator MMF subharmonics induce relevant EMFs in the rotor at rated speed. The design procedure is carried out using analytical models.