Sizing of the Suspension Converter Power Electronics for Bearingless Motors

This paper presents a methodology to determine converter ratings for bearingless motors based on the static and dynamic forces that act on the rotor. Bearingless motors generate both radial force and torque, enabling rotor rotation without mechanical bearings. To create the required forces in a bearingless motor, an additional power electronic converter is needed to supply the suspension currents. Accurate sizing of this converter is essential to ensure stable suspension, high power density, and cost-effectiveness, but has not received sufficient research attention to-date. In this paper, suspension converter requirements are derived for commonly used winding configurations, including: separate, multiphase (MP), multiphase with a dual-neutral point (DNMP), parallel and bridge dual-purpose no-voltage (DPNV), and mid-point current injection (MCI) windings. The paper compares the converter parameters and finds that MP, DNMP, and MCI require the highest DC voltage but lower capacitance, while parallel, bridge, and separate windings require the lowest DC voltage but higher capacitance. The bridge configuration is found to require significantly higher DC link capacitance than all other configurations as a result of the second-harmonic rinnle in the DC link current.