Permanent magnet bearingless motors: Modelling, design and drive

In this paper, the authors give a general description of bearingless machines and the origin of the ripples of the levitation force. Magnetic model using spectral analysis of the air-gap flux density is developed to identify the forces ripples and their origins. The authors propose two ways to suppress the force ripples. The first one can be performed during the design process of the machine while the second one can be applied with the supply via a control loop and an active harmonic suppression.