Hybrid Active-Passive Operation of a Passively Levitated Self-Bearing Machine

Passively levitated self-bearing machines relying on a combined armature winding have been recently developed so as to allow the systems that implement them to reach higher reliability and compactness while lowering their cost and complexity. The axial guidance being achieved through electrodynamic phenomena based on induced suspension currents, the restoring force is small at low speeds. External loads may therefore prevent the rotor from being magnetically suspended below a threshold speed. In this context, this extended abstract introduces and validates an innovative hybrid active-passive operation of these self- bearing machines. It consists in regulating the rotor axial position, and thence the restoring force, through the direct-axis component of the currents owing in the combined winding until the threshold speed beyond which passive levitation can be achieved is reached. The proposed active operation solely requires an additional axial position sensor. As a result, the benefits offered by passive suspension are not significantly impacted.