Evaluation of One- and Two-Pole-Pair Slotless Bearingless Motors With Toroidal Windings

In this paper, winding topologies for one- and two-pole-pair rotors are analyzed and compared for a slotless bearingless disk drive with toroidal windings. The basis of the studies is a six-phase motor with a diametrically magnetized one-pole-pair rotor. Due to the absence of mechanical bearings and the significantly large air-gap capability, the motor is suitable for applications with high purity and special chemical demands. Its slotless design results in low losses even at high rotational speeds. To improve the operational behavior of the rotor in different applications, the influence of higher pole pair numbers on the passive bearing stiffness is examined. A possible winding configuration for these rotors is proposed and evaluated for their bearing and motor performance. Based on the results, a further prototype was built and is presented in this paper.