I. Introduction
Axial flux permanent magnet machine (AFPMM) actually has small volume, high power density, small rotor inertia and large torque to weight ratio compared with radial flux machine [6]. It is widely used in occasions where requires compact axial space of motors, such as wind power generation, air conditioning compressor, and UAV rotor. AFPMM has attracted more and more attention in the field [1], [3].