Influence of Load on Optimal Rotor Skew Angles for Minimum Torque Ripple in Interior and Surface PMSMs

The influence of load conditions on the effectiveness of rotor skew in interior and surface permanent magnet synchronous machines (PMSMs) and the determination of the optimal skew angles for minimizing the on-load torque ripple are investigated. Herein, both continuous and stepped skews are considered. It is found that the effectiveness of the rotor skew depends on the load/electric loading and magnetic saturation and is generally inferior in interior PMSMs (IPMSMs) than in surface-mounted PMSMs (SPMSMs). The conventional skew angle, that is, the one on-load torque-ripple periodicity, works well in SPMSMs under light-load conditions. However, when SPMSMs are under heavy-load conditions with significant magnetic saturation or IPMSMs are under all load conditions, an optimal skew angle exists to simultaneously deliver a higher average torque and lower torque ripple than those obtained with the conventional skew angle. This is regardless of whether a continuous or stepped skew is applied. Therefore, a tradeoff between the optimal skew angle, torque production, torque ripple, and load conditions should be considered carefully when selecting skew strategies for different applications.