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Recently, fractional-slot windings with two-slot coil pitch are receiving more and more attention due to their lower space harmonic contents in stator magnetomotive force (MMF) compared with the widely-used fractional-slot nonoverlapping counterparts. To further reduce the detrimental space harmonics for this type of winding, various solutions featured by varied coil turn ratios are investigated in this paper. Firstly, all the feasible slot and pole number combinations for fractional-slot windings with twoslot coil pitch are discussed. Secondly, two types of Slot Harmonic Only Windings (SHOW), i.e., SHOW I and SHOW II, are illustrated on the 18-slot/10-pole (18S10P) and 24S10P windings, through which only the main harmonic and its slot harmonics will be present in stator MMF harmonics. Then, to overcome the drawback of reduced main harmonic magnitude owing to both the decreased winding factor and poor slot area utilization associated with the SHOW, two solutions, i.e., 6-0 solution and 5-1 solution for 18S10P and four alternatives, i.e., 7-1 solution, 6-2 solution, 5-3 solution and 4-4 solution for 24S10P, are proposed based on the SHOW I or SHOW II. It is found that the 5-1 solution for 18S10P and 5-3 solution for 24S10P winding are the most desirable ones considering the tradeoff between larger main harmonic magnitude and lower harmonic contents. Furthermore, electromagnetic performance comparisons are carried out between 24S10P permanent magnet (PM) machines with 5-3 solution and 12S10 two layer and 24S10P two layer machines. Although the average torque of the 24S10P machine with 5-3 solution has a slight decrease, its torque ripple and radial magnetic force density rotor eddy-current losses are greatly suppressed compared with the two layer counterparts. INDEX TERMS Fractional-slot winding, slot harmonic only, space harmonic, two-slot coil pitch.

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Permanent magnet (PM) machine with consequent pole (CP) rotor can improve the PM utilization ratio. However, one group PMs with the same polarity is replaced by iron core which deteriorating the electromagnetic performance of the machine, including even-order back-EMF harmonics, torque ripple, as well as unipolar leakage flux. Therefore, CP PM machine with various magnetic pole, i.e., equal pole-arc magnetic pole (EMP) and asymmetric magnetic pole (AMP) structure is proposed, with smaller torque ripple can be achieved, without deteriorating the torque ability compared with the conventional CP PM machine. Further, the influence of various CP PM magnetic pole on the end leakage flux is analyzed by three-dimensional (3-D) finite element (FE), which includes leakage flux distributions as well as magnetization of shaft. The electromagnetic characteristics of the machine with EMP and AMP rotor are compared with traditional surface-mounted and CP PM machines by FE analysis. It is demonstrated that EMP and AMP rotor structure can reduce even-order harmonics, torque ripple and end leakage flux for the machines. Finally, one prototype with CP AMP rotor is tested to confirm the theoretical and FE analysis, which includes suppression effect of even back-EMF harmonics, torque characteristics as well as leakage flux at the end shaft. INDEX TERMS AMP, CP rotor, EMP, even-order back-EMF harmonic, PM machine, torque ripple, unipolar leakage flux.