Design of Ultrahigh Speed Axial-Flux Permanent Magnet Machine With Sinusoidal Back EMF for Energy Storage Application

This paper focuses on the design and the analysis of an ultrahigh speed axial-flux permanent magnet (AFPM) machine for an aerospace flywheel energy storage system. The superiority of the proposed AFPM machine is the material-efficient PM shape, which contributes to obtain a sinusoidal back electromotive force (back EMF) and, hence, reduces the torque pulsations of the machine such as torque ripple. The harmonics present in back EMF have a large influence on iron loss and torque pulsations, which are always unacceptable in the applications involving the speed as high as 1 000 000 r/min. Analytical modeling is first performed to determine the PM shape for the proposed models. Then, the advantages of the proposed models are verified by comparing with the basic model with the conventional ring-shaped PMs using the 3-D finite-element method. The results show that the proposed models have a nearly ideal sinusoidal back-EMF waveform that significantly reduces the torque ripples compared with the basic model.