Investigation of modular odd-pole PM linear synchronous motors with flux gaps

Nowadays, to simplify manufacture process and improve fault-tolerant capability, more and more modular electrical machines are being applied in industrial areas. The purpose of this paper is to investigate a novel modular single-sided flat permanent magnet linear synchronous motor (PMLSM), which adopts segmented armature with the required flux gaps between segments to enhance the performance.

Using 2D finite element analysis, the performances, such as open-flux linkage, back-EMF, average thrust force, thrust ripple, etc., are compared in different values of flux gaps, as well as different slot/pole number combinations (mainly odd numbers of poles). Finally, to show the difference of linear motor from rotary one, the detailed comparison is made between modular PMLSM and rotary PMSM.

Due to flux gaps, it is found the electromagnetic performances are worsened along with flux gap width increasing to modular PMLSMs having slot number higher than pole number, but some aspects of performances such as winding factor, open-circuit flux linkage, back-EMF and average thrust can be improved to those having slot number lower than pole number. Due to the end effect of linear format, the thrust ripple is not significantly improved.

It is concluded the proper flux gaps can be chosen to improve the performance of PMLSM with certain slot/pole combinations. A new structure of 12-slot-13-pole (hereinafter referred to as 12s/13p) PMLSM with fractional slot and alternative-teeth wound winding is designed.