Weight optimisation of coreless axial‐flux permanent magnet machines

Abstract

This study explores the upper limits in power-to-weight and torque-to-weight ratios of coreless axial-flux machines with permanent magnets. Moreover, it provides a comprehensive multifunctional optimisation procedure that is utilised for obtaining these limits. The procedure encompasses analytical analysis of electromagnetic , thermal and structural (mechanical) aspects of axial-flux machines. Obtaining global minima is ensured by considering the whole machine design space, and mapping it into the performance space, where a Pareto front can be easily identified. From it, an optimal motor/generator for airborne wind turbines is identified. The design has a power-to-weight ratio of 6.4 kW/kg (19 Nm/kg at 3200 rpm) including structural (purely mechanical) parts, at an efficiency of 95%. This is a significantly higher ratio than the one in modern commercial machines or designs reported in the literature. Therefore, the resulting machine is manufactured and experimentally tested in order to verify the claimed limits and the optimisation methodology.

Ironless Axial Flux Wind Turbine Motor with Two Cylindrical Magnet Rings

“…In this structure, the iron in the stator is not mandatory [4]. Still on this structure, it is possible to use Halbach array magnets [5]. This allows the magnetic fields on the stator to be canalized even further.…”

“…Tile-shaped magnets are most often used to maximize the area of magnet covering the energized conductors [12]. However, parallelepiped magnets [5] or cylindrical magnets [3][13] can be used for cost or assembly reasons.…”

“…Next references indicate from equations, how to choose the dimensions of an AFPM with iron [7][14] or without [5] [15] for a wind turbine. The purpose of this article is to size an ironless axial flux motor from the dimensions of preselected magnets.…”

Design and construction of new axial‐flux permanent magnet motor

“…Air‐cored PM machines are attractive options for high‐speed applications due to the elimination of the stator core loss [14, 15]. On the other hand, all conductors are exposed to the air‐gap flux density [16, 17]; hence they have larger eddy currents, which is more critical at higher speeds. This forces the application of thinner conductors and a larger number of turns and strands, necessitating the consideration of expensive Litz wires [18].…”

Analysis of end effect in ironless stator AFPM machine via MEC model

“…Therefore, the conventional leakage fluxes are weakened in the machine due to the flux concentrating effect of Halbach-array PMs, whereas end leakage fluxes must be considered. For the ironless stator AFPM in [17], there is an about 10% back-electromotive force (EMF) results error of the electromagnetic analytical model without considering end leakage fluxes compared with finite element analysis (FEA).…”