Closed loop performance of a slotless Lorentz self-bearing motor

In previous work the authors presented a Lorentz self-bearing motor design targeted for precision pointing and smooth angular slewing applications. The motor also offers potential advantages when operated as a synchronous machine at high speed including larger power densities and shorter shafts. In this paper, the closed loop performance of the motor at low transient speeds (0 - 588 rpm) is presented. Using these results, several challenges to achieving high-speed rotation are identified and discussed. The most significant is the heavy cross coupling within the actuator which limits bearing stiffness and stability, and is amplified at rotor natural frequencies resulting in potential loss of levitation when passing through critical speeds. Of particular interest is the discovery of a significant cross coupling effect between the radial and tangential directions. A theory is put forth explaining this effect.