Fully Passively Levitated Self-Bearing Machine Implemented Within a Reaction Wheel

Abstract

Self-bearing machines offer a highly integrated solution to achieve the rotor drive and magnetic levitation within a single structure. Although the trend is toward a diminution in the number of actively stabilized degrees of freedom to reduce the requirement for sensors, power electronics, and controllers, no self-bearing machine relying solely on passive phenomena has been successfully tested so far due to the restrictions highlighted by Earnshaw's theorem. Recent researches have demonstrated, through electromechanical models and in-depth experimental investigations, that electrodynamic thrust self-bearing machines (EDTSBMs) can gather, within a combined winding, both the rotor axial passive suspension and motor functions. Nonetheless, the test rigs implementing them still comprised external means to ensure the rotor radial and tilt support. In this context, this article takes the study of EDTSBMs to the final step by combining them with two permanent magnet centering bearings, yielding the first fully passively levitated self-bearing machines. A reaction wheel demonstrator based on the latter is designed and sized according to an optimal approach. Thorough experimental analyses dealing with the axial forces that support the rotor and its resulting axial position as well as the drive torque are carried out, notably proving that stable fully passive levitation can be achieved. Finally, the motor and suspension currents as well as the corresponding losses are investigated.