Double-rotor ironless radial flux permanent magnet machine

Abstract

The use of electric machinery is often restricted or complicated in weight-sensitive applications such as light vehicle propulsion due to the amount of heavy ferromagnetic materials generally required. An existing Double-Rotor, Radial Flux, Air-cored Permanent Magnet (D-RFAPM) design was altered by adding inter-pole azimuthally oriented magnets to complete the flux path instead of a ferrous yoke. This allows the use of lighter nonmagnetic materials, e.g. aluminium or carbon fibre plastic, for structure. A simple 1-D magnetic model was used to perform initial design and gauge the thickness of magnets required. Detailed electromagnetic design was done using Finite Element Analysis(FEA), especially to determine the shape of the radial flux density distribution in the centre of the stator windings. With a sinusoidal distribution, voltage and torque constants can be calculated using the same approximations as for the D-RFAPM design. A prototype was constructed in order to achieve a proof of concept. Initial tests gave favourable results indicating near sinusoidal induced voltage waveforms and adequate performance achievement. The research and resulting prototype represent the early stages of a concept that both requires and merits further investigation.