Design of ultra-high speed axial flux permanent magnet machine with sinusoidal back-EMF

The use of small ultra-high speed rotating machines has been an area of interest for emerging applications such as machining spindles, dental drills, compressors and turbochargers, as well as portable power generation and energy storage systems. Such machines are being designed to operate at speeds reaching as much as one-million revolutions per minute (rpm). At such a high speed, a slotless axial flux permanent magnet machine having a simple air gap winding becomes an attractive option. However, the machine performance in terms of torque pulsations and losses must be minimized to ensure smooth operation. In this paper, a novel machine design is presented to achieve a nearly ideal sinusoidal back-EMF by special shaping of the permanent magnet.