Influence of stator slot openings on losses and torque in axial flux permanent magnet machines

Among the different geometrical parameters to be chosen during design of axial flux permanent magnet synchronous machines, the width of the stator slot openings near the air gap is an important parameter: it has a major influence on the power loss in the stator core and in the permanent magnets on the two rotors of the studied type of axial flux machines. Moreover, the stator slot openings parameter has a converse impact on both power losses. On the one hand, the increase in stator slot openings results in a reduction of the power losses in the stator core elements. On the other hand, it also results in increased loss in the permanent magnets. Also the torque is reduced for large but also for very small slot openings. This paper deals with axial flux machines of the YASA type: yokeless and segmented armature. It is shown that the slot openings contribute to an unequal flux density level over the different laminations in the stator core. Insight in the impact of the slot openings variation on both power losses (in stator iron and in permanent magnets) is provided, and an illustrative case is discussed in which the impact of the slot openings variation on both power losses is examined quantitatively.