Principles of magnetic levitation force and motor torque generation by superposition of harmonics in bearingless brushless motors

In this paper the principles of motor torque and suspension force generation in bearingless brushless motors with high pole numbers are explained, graphically illustrated and analyzed in detail. The necessary harmonic components of the flux density in the air-gap are calculated and it is visualized how these can be generated by superposition of harmonics depending on a specific rotor pole / stator slot ratio. Especially, for bearingless motors with a fractional pole / slot ratio, it is shown how superior suspension performance and high rotational speeds can be achieved. The considerations are exemplified for a 26-pole / 24-slots bearingless brushless motor.