A Novel Multi-Layer Structure for Axial Flux Machines

In an axial flux machine (AFM), an effective air-gap area is a ring form of which the size is decided by the outer and inner diameter of the stator. The inner diameter is usually not small, which leaves a relatively large inner space unused because the slot size has to keep uniform radially for current density. This article proposes a multi-layer structure that adopts concentric rings consisting of multiple layers instead of the conventional single layer. A conventional single-sided axial flux permanent magnet synchronous machine (AFPMSM) is introduced as a baseline design with 110 kW output power and 350 mm outer diameter. Through transforming this baseline design, the benefit of this new structure has been revealed with three different investigations in this article: 1) the output power per mass can be improved; 2) the compactness (output power in a limited space) can be increased; and 3) the constant power speed range could be significantly extended with a new type inverter (only design specification of the new inverter given), in which no additional technique of flux modulation required. The proposed multi-layer structure bypasses the issue that the area of a single ring cannot be enlarged due to the limitation of inner diameter. The air-gap area can be extended to the complete inner radial space for generating electromagnetic force. Besides, two factors, i.e., the number of layers and the coordination between multiple layers, make the performance of AFM highly customizable for different design objectives.