Design of variable air gap axial flux permanent magnet machine for extending the speed region

For extending the speed region of axial flux permanent-magnet (AFPM) machine, this paper presents a novel AFPM, which air gap length can be variable dynamically in operation. The variable mechanism, electromagnetic design method, flux-weakening performance and so on are all analyzed, and then a 5kW 77.5Nm variable air-gap AFPM is designed to compare with a fixed air-gap AFPM.