Improving a Cogging Torque Reduction Technique for Fractional Slot Numbers in a Permanent Magnet Machine

Abstract

For this paper, an improvement to a cogging torque reduction technique was studied in regards to integral slot numbers in a permanent magnet machine. An 18 slot/8 pole permanent magnet machine structure was selected and developed, and some axial channels were introduced to the machine’s rotor core. The effects the axial channels had on cogging torque reduction were not studied in detail; however, it was noted that the channels did not disturb the machine’s normal magnetic flux in regards to an air gap. Two slotting steps were used on the edge of the machine’s permanent magnet with slot opening widths of 2 mm and air gap lengths of 1 mm; this was done in order to minimize cogging torque. Three different magnet structures for the permanent magnet machine were then analyzed and compared. The two steps for slotting were found to be best for cogging torque reduction among the three different structures. Finally, simulation results showed that improving slotting steps for magnet edges could significantly reduce cogging torque in permanent magnet machines by up to 98.80%.