Magnet shifting for back EMF improvement and torque ripple reduction of a TORUS-type nonslotted axial flux permanent magnet machine

Permanent magnet (PM) shifting method is one of the ways to improve performance characteristics of PM machines. In this paper, PM shifting method is employed to reduce total harmonic distortion (THD) of the back EMF and torque ripple of a TORUS type nonslotted axial flux permanent magnet (TORUS NS-AFPM) machine. To fulfill this goal, a formula for calculating back EMF waveform of the machine with shifted PMs is proposed. A 3.7 kW, 1400 rpm TORUS NS-AFPM machine is selected as case study machine and the accuracy of the proposed formula is confirmed with the help of three-dimensional finite element method (3-D FEM). Then by using proposed formula, the effect of PM shifting angle on the back EMF waveform of the machine is investigated. In addition, the case study machine is fabricated and back EMF waveform of the machine with different value of PM shifting angle is analyzed using experimental results. With the help of proposed formula and 3-D FEM the effect of PM shifting angle on the torque ripple of the machine is studied. In addition, a procedure for calculating optimum value of PM shifting angle is proposed. The obtained results show the effectiveness of the PM shifting method on improving machine back EMF waveform and torque ripple.