Unbalanced magnetic force mitigation in 3-slot/2-pole permanent magnet machine by inserting auxiliary slots

Abstract

High speed machines have received much attention recently. However, unbalanced magnetic force (UMF) may occur in some slot/pole number combinations even 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 permanent magnet (PM) machines with different auxiliary slots are investigated and compared in this paper. In the first two machines, namely Machine 1 and Machine 2, the auxiliary slots are inserted in the middle of 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 rated on-load condition in the third machine, viz. Machine 3. Comparing 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 performance, such as flux linkage, back EMF, cogging torque, rated output torque and torque ripple are compared. The influence of working conditions is investigated as well.