Low torque ripple tooth coil windings multi-3-phase machines: design considerations and validation

In multi-n-phase machines, the n-phases are grouped in separated stars. A particular subcategory of multi-n-phase machines is the multi-3-phase machines. This study presents the design considerations and their validation for tooth coil wound multi-3-phase machines. A generic algorithm to design multi-3-phase machines is proposed. Although this study mainly focuses on multi-3-phase machines the approach is generalised and is applicable to any multi-n-phase machine. The resulting machines exhibit a low torque ripple value, and a mathematical formulation is proposed in order to justify this behaviour. All the multi-3-phase machines designed according to the proposed algorithm can be studied, and directly compared, thanks to the generalised harmonic formulation of the stator MMF and the torque performances here proposed. This study is enriched with some design hints useful to realise a machine with low mutual coupling between phases, and some considerations that can help the machine designer in the choice of the number of poles. The design algorithm is applied for the design of a triple-3-phase PM-inset machine solution, with nine slots ten poles. The performances, evaluated by finite element analysis and experimental analysis, demonstrate the effectiveness of the design algorithm proposed in a very simple structure machine.