Cogging Torque Cancellation by Magnet Shaping in Surface-Mounted Permanent-Magnet Motors

This paper presents a new method for cancellation cogging torque by magnet shaping. First, the conditions to be met by the induction space wave for the total cancellation of cogging torque are analytically established. These results are then used to determine the shape of the magnets. The approach followed is inverse to that used by traditional methods, whereby, based on a predetermined shape of the magnets, the cogging torque is calculated. As a result, the proposed method enables optimum results to be obtained directly and it is generalizable to any motor configuration. The methodology has been first validated by means of finite elements and then tested experimentally on a dc motor and on an ac motor for both radial and parallel magnetization.