Integer-slot vs fractional-slot concentrated-winding axial-flux permanent magnet machines: Comparative design, FEA and experimental tests

In slotted axial-flux permanent magnet machines two possible concentrated-winding arrangements can be used: integer-slot and fractional-slot. The former type, i.e. windings with a number of slots/pole/phase equal to one, has long been a preferred choice with machine designers due to its simple layout. On the other hand, fractional-slot concentrated-winding machines have been the focus of a significant amount of international research in the past decade. This paper presents an original comparison between two 10 kW axial-flux permanent magnet machine prototypes with concentrated-windings: a 20 pole, 60 slot integer-slot concentrated-winding machine and a 20 pole, 24 slot fractional-slot concentrated-winding machine. The design of both machines is described, highlighting the constraints that have been set to allow a fair comparison between them. Static and time-stepped finite element analysis results are presented. Comparative no-load and load tests are performed on full scale prototypes and the results are reported. Finally, conclusions are made regarding the performances and required trade-offs for both machines.