Analytical modelling of modular and unequal tooth width surface-mounted permanent magnet machines

This paper presents simple analytical modelling for 2 types of 3-phase surface-mounted permanent magnet (SPM) machines such as modular and unequal tooth width (UNET) machines with different slot/pole number combinations. It is based on the slotless open-circuit air-gap flux density and the slotted air-gap relative permeance calculations. This model allows calculating the open-circuit air-gap flux density, phase flux linkage and back electromotive force (EMF), average torque of both the modular and UNET machines. Its accuracy has been validated by 2D finite element (FE) method. A flux focusing/defocusing factor has also been introduced to analyse the influence of flux gaps in alternate stator teeth of modular machines on the machine electromagnetic performances. It has been found that by properly choosing the slot/pole number combination and flux gap width, the open-circuit air-gap flux density, the winding factor and the flux focusing effect can all be improved. As a result, the performance of modular machine can be significantly boosted. The analytical and FE models have been validated by experiments.