MMF and torque of five-phase fault tolerant permanent magnet synchronous motor

In order to explain the reason of torque change after open-circuit failure for five-phase fault tolerant permanent magnet synchronous motor (FTPMSM), the distribution of stator magnetic motive force (MMF) harmonics was investigated by adopting the winding function. Under open-circuit fault without adjustment, the relationship between MMF and torque was revealed by analyzing the time-space distribution of main harmonic MMF, and the main reason that torque ripple increases after open-circuit fault was explained. Under this situation, the stator MMF appears harmonics of 5k and 10k±3 orders, but the total eddy-current losses induced by the MMF harmonics decrease because of the amplitude decline of slot harmonics. When the current control strategy is applied to adjust the failure, the average torque can basically increase to the normal value. However, the torque ripple is still larger than normal case, due to the existence of the second and fourth ripple torque. At the same time, the amplitudes of MMF harmonics of 10k±1 order increase to the normal level, whereas the harmonics of 10k±3 order still exist and their amplitudes increase a lot. Therefore, the total rotor losses become larger as compared with the normal condition.