On the design of fractional slot T-LPMSMs: effect of the slot-pole combination

The paper deals with an approach aimed at the design of fractional-slot tubular-linear permanent magnet synchronous machines (T-LPMSMs) with emphasis on the effect of the slot-pole combination. Following the description of the T-LPMSM concept under study, the developed approach is initiated by a formulation of the air gap flux density, based on the resolution of the magnetic potential vector equation in the air gap and PM regions which enables the prediction of the cogging force and the phase back-EMFs. The effects of the slot-pole combination on these features is considered in the second part of the study which is achieved by the selection of an optimized slot per pole and per phase number that yields a high phase back-EMF amplitude and a low cogging force peak-to-peak value. A case study considering the optimized slot per pole and per phase number is treated where the analytically predicted results are validated by finite element analysis.