Static eccentricity effect on no-load performance of FSCW PM machines with series and parallel windings

In this paper, static eccentricity fault is studied for open-circuit characteristics of fractional slot concentrated winding (FSCW) permanent magnet (PM) machines. Both series and parallel winding arrangements are analysed separately, and finite element and analytical methods are utilized to give full explanations about machine's performance. It is shown that Back-EMF of the surface mounted PM machine is not changed in both series and parallel winding connections after eccentricity fault. Compensation effect between phase groups and high ratio of PM to air gap thickness are responsible of such behaviour in series and parallel wound machines respectively. It is also shown that the increased cogging torque after eccentricity fault is due to interaction between the original field components (without eccentricity) and the additional components due to the eccentricity of the same order. Furthermore, it is proven than the unbalanced magnetic pull is generated due to interaction between air gap magnetization harmonics and additional eccentricity harmonics of the order differed by 1. The results presented in this paper are valid for other FSCW PM machine with various slot-pole combinations which have symmetry order of more than unity.