Design and analysis of multi-pole Halbach (self-shielding) cylinder brushless permanent magnet machines

Halbach magnetised permanent magnet cylinders, which are sometimes referred to as current sheet equivalent materials, have been used extensively for beam focusing in magnetic lenses and free electron lasers etc. However, their self-shielding property and their ability for creating relatively strong multi-pole, sinusoidally distributed magnetic fields in the internal air-space makes them potentially attractive for use in high-speed brushless machines. In this paper, relevant design and analysis equations for permanent magnet brushless AC machines in which a multi-pole magnetised Halbach cylinder acts as the external rotor are presented. The novel features of such machines are then illustrated through two potential applications, viz: a multi-axis roller system for sheet material handling, for which acceleration and positional accuracy are key performance factors; and a flywheel storage/supply system for peak power handling in electric vehicles, for which a high efficiency and low idling losses are important requirements