Investigations on cogging torque mitigation techniques of transverse flux motor for direct drive low-speed spacecraft applications

The transverse flux motor (TFM) is an ideal choice for direct drive high torque applications owing to its proven higher torque density compared to the radial flux and axial flux motors. TFM motors have several merits to be used for spacecraft applications, considering the everlasting demand of the industry for reduction in power and mass. This paper investigates the various cogging torque mitigation techniques for transverse flux motor to be effectively used as the drive motor for precise position control spacecraft requirement. The paper discusses the basic design variables of surface mounted TFM (SM-TFM) that are to be considered for minimizing the cogging torque. The effectiveness of cogging torque mitigation techniques are presented for two cases of SM-TFM, one with maximum cogging torque and the other with minimum cogging torque. The different torque ripple minimization techniques studied include skewing of rotor poles, notching of the stator poles, introduction of asymmetry in the stator structure, provision of wedges by the side of poles, segmentation of the magnets and introduction of shunt. The effectiveness of these cogging torque mitigation techniques is studied on two hardware variants of the TFM, one with the modified stator having shunt and the other with the modified rotor having low remanence permanent magnet. The TFM with a shunted stator is effective in torque ripple reduction in addition to the improvements in electromagnetic torque.