Design of Consequent Pole Synchronous Motors with High Reluctance Torque Utilization by Soft Ferrite

Abstract

In this thesis, a novel structure of rotor is proposed to utilize the high reluctance torque while maintaining a similar level of magnetic torque, ultimately to ensure high total torque. The frozen permeability method is utilized to segregate the total torque into its reluctance and magnetic torque components. During this process, it maintains the same usage of PM and the same magnetic poles with CPMSM. The number of rotor pole in the proposed CPMSMs are double as compared to the conventional CPMSM, in order to shift the d-axis of maximum reluctance torque, and approach to the d-axis of maximum magnetic torque. The air gap flux barrier in proposed CPMSMs is used to prevent the flux flowing from one magnet to another magnet with opposite polarity, for reducing unipolar leakage flux and improving torque performance. Furthermore, the soft ferrite material with low saturation magnetization is used in the consequent pole to suppress magnetic unbalance, caused by the consequent pole rotor, ultimately achieve the aim of reducing torque ripple. The performance of SPMSM, CPMSM, proposed CPMSMs are analyzed by the 2D-FEA. In comparison with the conventional CPMSM, the total torque of the proposed CPMSM with soft ferrite pole is increased by 12%, while the torque ripple is decreased by 6.8%. Moreover, two key parameters are discussed to obtain a better output performance. The sensitivity analysis is used to verify the impact of two key parameters on torque characteristics. It is confirmed that replacing all of the consequent poles with soft ferrite materials to replace all of the consequent poles, and by selecting the width of the air gap flux barrier will obtain a better torque characteristic. As the results show, the key parameters design motor demonstrates a good performance with the improved output torque as well as reduced torque ripple and amount of soft ferrite when compared with a conventional design.