MAGNUS — An ultra-high specific torque PM axial flux type motor with flux focusing and modulation

Abstract

Axial flux permanent magnet (AFPM) synchronous motors are attractive for low speed direct drive systems because of their high specific torque. The present paper proposes a novel axial flux machine topology, called MAGNUS, obtained by combining a yokeless central stator type NS arrangement with two external high polarity spoke-rotors, resulting in very high flux concentration. The stator, which includes main and auxiliary teeth for air-gap profiling has a small number of concentrated coils. Two stator configurations are discussed, the first, a yokeless construction with coils wound around the teeth, and the second with coils placed around the stator core in a Gramme ring arrangement. Feasible slot pole combinations are identified. High torque densities are achievable owing to torque magnification achieved by air-gap profiling as well as flux concentration. Initial analysis indicates that this machine presents higher torque than a YASA machine, which currently holds a record for torque density.