Due to the absence of magnetic teeth on the stator to restrict the magnetic field, the windings of the slotless
motor are directly exposed to the air gap magnetic field. Consequently, this exposure results in a more irregular
distribution of current in the windings and a notable increase in AC loss. Therefore, it is the key point in the
design of slotless permanent magnet motor (SPMM) to study the characteristics of AC copper loss in detail and
the effective suppression method. According to the structural characteristics of SPMM, this paper proposes to
reduce the gap between wires (WDG) to reduce the AC copper loss. And the corresponding winding production
method - winding extrusion potting (WEP) for toroidal windings is also introduced. In addition, the measurement
method of WDG is demonstrated through experiments, and the accurate value of WDG before and
after using this suppression method are obtained. The research results indicate a 46 % reduction in AC copper
loss attributed to circulating current. Ultimately, the experimental outcomes of the prototype align well with the
theoretical analysis and computational findings.