Comparison of two- and four-pole rotors for a high speed bearingless drive

Bearingless drives have found their way into several industrial applications such as pumps, fans and chemical process chambers. In contrast to these drives which run at speeds below 15.000rpm, the suitability of bearingless drives for high speed has first been demonstrated with a bearingless disk drive running up to 115.000rpm in previous works by the authors. This drive uses a permanent magnet rotor with a pole number of two in order to constrain iron losses and generate the highest rotor speed with a certain electrical frequency. Other design criteria such as the rotordynamic behaviour, the radial bearing force or the torque capacity, however, might benefit from a higher pole number. Therefore, this paper will present the comparison of a two-pole and a four-pole rotor for the use in a high speed bearingless drive.