Modeling and Optimization of Hybrid Magnetic Bearings Considering Touchdown Bearings for Ultra-High-Speed Turbomolecular Pumps

The impeller end of the ultra-high-speed magnetically suspended turbomolecular pumps (MSTMPs) is characterized by considerable size and mass, necessitating a high load capacity for the hybrid magnetic bearing (HMB) and high-reliability protection for the touchdown bearing (TDB). However, the limited size of the MSTMPs results in a compact and integrated arrangement of the HMB and TDB, which introduces difficulties to the design process. Additionally, the inherent magnetic permeability of the TDB introduces extra negative stiffness, causing deviations in support stiffness and affecting system stability. This article focuses on analyzing and optimizing the support stiffness to design high-performance HMBs for MSTMPs. First, a combined electromagnetic model of HMB and TDB (HMB-TDB model) is proposed as a new research subject. The negative stiffness introduced by the TDB is quantitatively analyzed using this model. Based on the above analysis, a cooptimization method for the HMB-TDB model is proposed, which simultaneously considers axial length minimization and negative stiffness minimization. The proposed approach enables MSTMPs to achieve stable operation at higher rotational speeds. Finally, finite element method (FEM) analysis and prototype testing are conducted to validate the accuracy of the HMB-TDB model and to confirm the feasibility of the proposed optimization scheme for ultra-high-speed MSTMPs.