Sensitivity of Manufacturing Tolerances on Cogging Torque in Interior Permanent Magnet Machines With Different Slot/Pole Number Combinations

The cogging torque is usually very sensitive to the manufacturing tolerances during machine mass production, and this paper investigates the different sensitivities between interior permanent magnet (IPM) machines with different slot/pole number combinations. Exemplified by two typical combinations, i.e., 12-slot/8-pole and 12-slot/10-pole designs, the fundamental performance is first analyzed under ideal conditions. Then, with the tolerances of permanent magnet diversity and tooth bulges considered, the most sensitive cases are identified for the two machines, based on which the ultimate values of additional cogging torques are obtained and compared. In order to verify the different sensitivities, the field spatial harmonics in the two machines with and without considering the tolerances are further analyzed, from which the different origins of additional cogging torque components can be obtained. Finally, the IPM prototypes with and without amplified tolerances are fabricated and tested to verify the analyses.