Analysis and comparison of axial-flux permanent-magnet brushless-DC machines with fractional-slot concentrated-windings

This paper presents study of axial-flux permanent-magnet machines (AFPMMs) with fractional-slot concentrated-windings for brushless-DC (BLDC) operation. Four different AFPMMs are designed for in-wheel direct-driven electric vehicle, and are compared to study the effect of layer numbers, pole/slot combinations, and tooth widths on cogging torque, fault tolerance, and BLDC operation. As AFPMMs are inherently three-dimensional machines and modeling of them is so time-consuming, an accurate analytical model is used to predict the no load air-gap flux density distribution, flux-linkage, back-EMF, and cogging torque. The results are verified by three-dimensional finite-element (3-D FE) simulation.