Mitigation of unbalanced magnetic force in a PM machine with asymmetric winding by inserting auxiliary slots.

Permanent magnet (PM) machine has received much attention recently. However, unbalanced magnetic force (UMF) may occur in PM machines with some slot/pole number combinations even when there is no rotor eccentricity, which can cause high vibration and noise. In order to reduce the rated on-load UMF, three 3-slot/2-pole PM machines with different auxiliary slots are investigated and compared in this paper. In the first two machines, namely, machines 1 and 2, the auxiliary slots are inserted in the middle of the stator teeth, while their sizes are optimized under different working conditions, i.e., no-load and rated on-load conditions. In contrast, both position and size of auxiliary slots are optimized under the rated on-load condition in the third machine viz., machine 3. Compared with the conventional prototype machine, the maximum rated on-load UMFs are reduced by 6.3%, 50.7%, and 96.6%, and the rated output torques are decreased by 0.7%, 11.5%, and 4% in these three machines, respectively. In addition, the other electromagnetic performances, such as flux linkage, back electromagnetic force, cogging torque, rated output torque, and torque ripple, are compared. The influence of working conditions is investigated, and the experiments are also carried out to validate the numerically predicted results.