Influence of Stator Topologies on Average Torque and Torque Ripple of Fractional-Slot SPM Machines With Fully Closed Slots

Abstract

Abstract-This paper investigates the influence of concentrated winding configurations and stator core structures on torque performance of fractional-slot surface-mounted PM (SPM) machines. From analyzing the separated torque components of prototype SPM machines with 12-slots/10-poles (12S/10P) combination by frozen permeability (FP) method, it can be found that the torque ripple is closely related with local saturation in fully closed slot (FCS) machines. Besides, the heavier local saturation will also jeopardize the merit of using alternate teeth wound windings, such as obtaining higher average torque than electrical machines with all teeth wound windings. The further analysis of stator tooth relative permeability variation over one electrical period demonstrates that the major reason for torque ripple difference among these electrical machines with different stator topologies is the asymmetric saturation between the adjacent teeth. Both the subharmonic due to armature reaction (determined by winding connection and current value) and the asymmetry of stator core structure contribute to such asymmetric saturation. In order to more clearly verify this, the complementary slot/pole number combination (12S/14P) is also analyzed. The conclusion is effective for electrical machines with other slot/pole number combinations as well. Experiments have been carried out to validate the predictions.

Research on a Limit Analytical Method for a Low-Speed Micro Permanent Magnet Torque Motor with Back Winding

“…Fractional slot concentrated winding was used in this study because of its advantages of high torque density and high slot filling coefficient [20]. The slot type of the BWPMTM is equivalent to the closed slot, which can effectively reduce the torque ripple and improve the running performance [21,22]. As shown in Figure 1c, there is a magnetic barrier (the connection between the bottom of the slot and the inner surface of the stator) to maintain the integrity of the stator.…”

Modularity techniques in high performance permanent magnet machines and applications

“…It can be shown that for maximizing the torque, the width of the teeth with coils in 12S/10P unequal teeth PM machines should be wider, while the width of the teeth with coils in 12S/14P unequal teeth PM machines should be narrower. The issue for using unequal tooth width stator is relatively large torque ripple, which is owing to heavier local saturation [62]. The modular stators in [33], [34], [63], [64] have flux barriers alternately in stator yokes, as shown in Fig.…”

Torque ripple suppression of permanent magnet synchronous machines by minimal harmonic current injection

“…In the perspective of the machine design‐based methods, optimising the winding distribution to improve the spatial magnetic field is commonly employed [2, 3]. The fractional slot and the skewed slot techniques in the stator are proved to be valid in weakening the cogging torque, even though the average electromagnetic torque can be discounted in some degree [4, 5]. Compared with machine design‐based techniques, the control algorithm‐based methods are more flexible and easier to implement and, therefore, attracts more attention from researchers worldwide.…”