Modeling, Investigation, and Minimization of AC Winding Loss in Slotless PM Machines

The AC winding loss can be the primary source of losses in slotless permanent magnet (PM) machines. This paper presents the simplified model, investigation, and reduction method of the AC winding loss in slotless radial flux PM machines. Preferentially, the open-circuit AC winding loss is calculated in the rotor reference frame based on the resistance limited. Subsequently, a fast optimization model, including the AC winding loss, is developed by solving the field equations only once for a specific geometry. As a result, the influence of the design parameters on the AC winding loss can be investigated by taking advantage of the fast computational model. It shows that the concentrated winding with multiples of 2-pole/3-coil is the best selection to achieve the low AC winding loss due to the possibility of using multiple parallel paths. Finally, the finite element (FE) and experimental results demonstrate the validity of the proposed analysis.