Effect of Magnet Coverage on Torque, Loss and Torque Ripple in a PMSM

This paper address the effect of magnet coverage on the torque, iron and magnet loss components and torque ripple of two surface permanent magnet synchronous generators of 5MW. The values of torque, torque ripple, iron and magnet losses are calculated using a FEM program. It is concluded that the optimal magnet coverage can only be found by extensive investigations for each specific machine. However, an estimate value of magnet coverage can be found from recommendations and formulas, including only the number of phases and the number of slots per pole per phase. It is shown that by investigating each individual machine for a magnet coverage between 0.7-0.9, the torque ripple can be reduced up to 40% and magnet loss can be reduced up to 28%.