Phase-Pole Combinations for Axial-Flux Permanent Magnet Machines With M-Phase Equidirectional Toroidal Winding

Multi-phase equidirectional toroidal winding (ETW) has prominent advantages in improving machine torque density and fault tolerance, which can be a superior scheme for electric vehicle applications. The PM pole number matched to different phases of ETWs significantly affects the torque performance, necessitating a comprehensive analysis. This article mainly investigates the superior phase-pole combination (PPC) of the dual-rotor axial-flux PM machine (AFPMM) with $m$ -phase ETW (MP-ETW) by evaluating its torque performance. First, the machine structures are presented and the armature field (AF) is investigated. It is shown that the main AF harmonic orders of the MP-ETW are ( $mk-1$ )th and [ $mk-(m-1)$ ]th, which provide the basis for possible PM pole number selection. Second, the torque performance of AFPMMs with the potential PPCs is evaluated with reference to that with the $m$ -phase and two-pole ( $m$ Ph2P) PPC based on 3-D finite element analysis (3-D FEA). Both slotless and slotted AFPMMs are investigated. The analysis results indicate that mPh2P is the superior PPC for slotless AFPMMs. In contrast, for slotted AFPMMs, higher torque density, and lower torque ripple can be achieved by adopting the PPC of $m$ Ph[2( $m-1)]\text{P}$ . Finally, a slotted prototype with the PPC of 3Ph4P is manufactured and tested to verify the correctness of the analysis.