Rotor Eccentricity Impact on Electromagnetic Behavior in Combined Winding Bearingless Motors Towards Displacement Self-Sensing

Levitation control of bearingless motors requires rotor displacement sensors. Recent research has explored self-sensing (sensorless) control which enables removing these sensors, but only for separated windings. Combined windings - where each coil can create torque and force - have been proven to be a critical component for realizing high performance bearingless motors for industrial applications. These applications are often cost-sensitive and require bearingless solutions with minimal overhead compared to traditional motors. Self-sensing control with combined windings removes barriers for wider adoption of bearingless technology - this paper forms the analytic basis for showing this is possible. The primary contribution is a unified modeling framework which encompasses several popular combined winding types found in the literature. For each winding type, winding functions are defined - each type with differing winding coil circuit arrangements and drive interfaces. The terminal inductance matrix and back-EMF is computed to include the effects of a non-centered rotor, and then transformed into decoupled torque and suspension force components. Through the presented transformations, all combined winding types support radial self-sensing, albeit with additional control complexity. Finite element simulations and hardware experiments validate the modeling approach. Future self-sensing research can build upon these models to design control algorithms and machines which work for any combined winding type.