Active controllable rotary superconducting magnetic bearings based on flux-pumped closed-loop coils

High-temperature superconducting (HTS) bulk-based magnetic bearings possess the advantages of self-stability and are well-suited for high-speed rotary systems. However, they suffer from levitation force decay issues and lack of controllability, which restrict their practical applications. To address these limitations, this paper presents the design and experimental validation of self-stable and actively controllable rotary superconducting magnetic bearings (SMBs) based on flux-pumped closed-loop HTS coils. The closed-loop HTS coils provide self-stability, and the integrated self-rectifier flux pumps wirelessly provide real-time magnetic flux modulation, allowing active adjustment of the levitation status. Experimental results show that the proposed system can: (i) eliminate levitation height decay, maintaining the rotor height within ±0.1 mm up to 3600 rpm; (ii) provide 10-mm dynamic levitation height control with high tracking accuracy; and (iii) actively counteract external axial loads of ±15 N, improving the effective axial stiffness. Furthermore, the influence of active flux modulation on axial self-stability is experimentally investigated. As the flux modulation intensity increases, the axial restoring force is progressively weakened, and the self-stability region correspondingly shrinks. These results demonstrate that flux-pumped closed-loop HTS coils enable actively controllable SMBs while preserving self-stability, offering a potentially feasible approach for applications such as flywheel energy storage systems and maglev motors.