Analysis and Implementation of an Enclosed Yokeless Stator for Axial Flux PM Motor With New Integer-Slot Distributed Independent Winding

In this article, a new integer-slot distributed independent winding is proposed for the yokeless stator axial flux permanent magnet synchronous motor (AFPMSM). Two sets of single-layer winding are wounded on the double sides of yokeless stator core in alternate directions. Through this method, the windings on both sides of the stator are naturally separated according to the number of pole pairs. The design motivation is to settle the internal direct oil-immersed cooling guide channel of the enclosed yokeless stator for the AFPMSM, without affecting the electromagnetic performance. Firstly, the new integer-slot distributed independent winding is introduced in detail. The electromagnetic performance of the proposed integer-slot distributed independent winding are compared with the conventional integer-slot distributed winding by finite element analysis (FEA) to demonstrate the design feasibility and artifice. Then, the structure-cooling design considerations are provided with a low-cost solution for the enclosed yokeless stator. The computational fluid dynamics (CFD) analysis results show that the stator components can be sufficiently cooled through internal guide channel of oil-immersed cooling. Finally, a full-scale oil-immersed cooling yokeless stator AFPMSM prototype are manufactured. The torque capability matches well with the FEA results. The temperature performance of the yokeless stator AFPMSM with the new integer-slot distributed independent winding using the proposed direct oil-immersed cooling is recorded during the test. The results show that the proposed new integer-slot distributed independent winding and internal direct oil-immersed cooling guide channel to be feasible, and furthermore, to provide significant improvements for the thermal management of yokeless stator AFPMSM.