Effect of stator chording and rotor skewing on average torque and torque ripple of reluctance synchronous machine

Low torque ripple in electrical machines is generally required to reduce acoustic noise and mechanical resonance vibration. To design for low torque ripple, however, affects the average torque and the power rating of the machine. In this paper, the effect of stator winding chording and rotor skewing on the average torque and torque ripple of the normal (transverse) laminated rotor reluctance synchronous machine is investigated. The 2-D finite element time-step method is used in the analysis. Only rotors with the number of flux barriers less than the number of stator slots are considered. It is shown and explained that chording has little effect on the torque ripple of the machine while it significantly reduces the average torque. Skewing the rotor, on the other hand, reduces torque ripple drastically, but has little effect on the average torque. It is further found that skewing the rotor by one stator slot pitch is not necessarily the optimum.