Torque Ripple Improvement for Ferrite-Assisted Synchronous Reluctance Motor by Using Asymmetric Flux-barrier Arrangement

Abstract

Ferrite-assisted synchronous reluctance motors (FASRM) provide high torque density and a wide range operation speeds for many applications, ranging from electric vehicle and electric home appliance [1]. Moreover, the ferrite magnet has received increased attention, following the increase of the price of rare earth magnet. However, the main drawback of the FASRM is the high torque ripple which will lead to serious vibration and acoustic noises [2]. Therefore, it is greatly significant to research the torque ripple suppression strategy for FASRMs, thus improving the smoothness of the torque [3]. This paper introduces a low torque ripple FASRM with asymmetrical flux barrier, which can reduce the torque ripple effectively. Novel Topology Fig. 1 shows the structure of the proposed FASRM. This motor has 48 slots and 8 poles, with two flux barriers per poles. The detailed configuration of the asymmetrical flux barrier is shown in Fig. 2. There are two kinds of flux barriers with different opening angle, and the changing of the angle based on the original flux barriers $B_{1}$. The opening angle of flux barriers $B_{2}$ is enlarged $\theta $ based on original flux barriers $B_{1}$. In this way, a shift of the torque waveform phase can be achieved, and the torque amplitudes offset each other. In addition, the amount and location of ferrite magnets have not changed, and reduce the torque ripple effectively without sacri- ficing the average torque. Results The proposed method is evaluated by a theoretical analysis and finite-element method (FEM). Fig. 3 shows the no-load field distribution and on-load flux density of the proposed FASRM. It can be seen that the magnetic fields are symmetrical distributions, and the asymmetrical flux barriers will not affect the electromagnetic performance of the proposed FASRM. Fig. 4 shows the reluctance torque waveforms and harmonics. As adopted the asymmetric flux barrier arrangement, a shift of the torque waveform phase can be achieved, and the torque amplitudes offset each other. It can be seen that the reluctance torque ripple is reduced from 85% to 24%, approximately. Fig. 5 shows total torques waveform and their harmonics. It can be seen that the total torque ripple is reduced to 14%, and the 6th and 12th harmonics have been successfully eliminated.