Zeqiang He, Tadahiko Shinshi
This article presents a method for simultaneous sensorless rotation and suspension control in a bearingless motor (BELM). Previous sensorless BELM studies have typically addressed either rotation or suspension in isolation, limiting system robustness, cost reduction, and compactness. Achieving simultaneous sensorless control has been hindered by two fundamental challenges: 1) acircular dependencyproblem: sensorless rotation control requires stable magnetic suspension, while magnetic suspension itself necessitates accurate rotor angle information; and 2) mixed electromotive-force signals arising from the coupling between armature and suspension flux linkages. To overcome these challenges, we introduce co-designed innovations in both motor structure and control algorithms. First, we propose a homopolar bearingless slice motor that combines a unique permanent magnet arrangement at the stator pole tips with a separated armature and suspension winding configuration. This structure enables rotor-angle-independent suspension force generation and effective decoupling of armature and suspension flux linkages. Second, the rotor electrical angle is estimated using fundamental-frequency stator voltages and currents, while the radial displacement is estimated via high-frequency signal injection. By separating the content of the measured signals using the phase terminal voltage for angle estimation and the coil terminal voltage for displacement estimation, the approach enables fully decoupled, simultaneous sensorless rotation and suspension. Experimental results obtained from a prototype system validate closed-loop sensorless rotation and suspension operation. Furthermore, a comparison between two rotor configurations—a solid-core rotor and a soft magnetic composite (SMC) rotor—reveals that eddy currents in the solid-core rotor introduce a phase lag in displacement estimation, whereas the SMC rotor effectively mitigates this effect.