Integral-Slot Versus Fractional-Slot Concentrated-Winding Axial-Flux Permanent-Magnet Machines: Comparative Design, FEA, and Experimental Tests

In slotted axial-flux permanent-magnet (PM) (AFPM) machines, two possible concentrated-winding arrangements can be used: integral slot and fractional slot. Integral-slot concentrated windings (ISCWs) have a number of slots/pole/phase equal to one and have long been a preferred choice with machine designers due to their simple layout. On the other hand, fractional-slot concentrated windings (FSCWs) have a number of slots/pole/phase less than one and 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 AFPM machine prototypes with concentrated windings: a 20-pole 60-slot ISCW machine and a 20-pole 24-slot FSCW 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 experimental tests are performed on full-scale prototypes, and the results are reported: Important tradeoffs in key aspects such as peak cogging torque, constant power speed range, and additional losses are demonstrated. Finally, conclusions are made regarding the performances and required tradeoffs for both machines.