Impact of the rotor back-iron resistivity on the rotor eddy-current losses in fractional-slot concentrated windings PM machines

It is well known that in fractional-slot concentrated windings the eddy-current losses in the permanent magnets can be relevant and, for this reason, they must be evaluated in the machine design procedure. The paper investigates the influence of the rotor back-iron resistivity on the rotor eddy-current losses in this machine typology. In particular, a external rotor annulus shape PM machine with fractional-slot non-overlapping concentrated windings is considered. The machine is a scaled representative prototype of starters/generators embedded in aircraft engines. Both the rotor back-iron and permanent magnet eddy-currents are simultaneously considered by means of bi-dimensional transient FEM simulations, including effects of stator slotting, rotor motion and material saturation. The analysis is conducted increasing the rotor back-iron resistivity from an ideal situation of a high-conducting material up to the opposite ideal condition of a non-conducting material. Adjusting the rotor back-iron resistivity, the space MMF harmonic components influence on the machine torque is qualitatively investigated and discussed too.