Modeling and Design of 3-DOF Magnetic Bearing for High-Speed Motor Including Eddy-Current Effects and Leakage Effects

The 3-degrees of freedom magnetic bearing (3-DOF MB) with permanent-magnet (PM) biased has been applied to high-speed motor progressively for their advantages of small thrust disk, low wind friction loss, and small volume. To predict performance and guide design of the 3-DOF MB, an accurate analytical model including eddy-current effects and leakage effects is proposed. Both the solid and the laminated cores are applied in the 3-DOF MB, and therefore the eddy-current effects in different core materials are modeled separately. The frequency response characteristics of axial and radial stiffnesses are calculated according to the proposed model. The analytical results show that the eddy currents induced due to the changing currents will result in considerable magnitude decrease and phase lag of stiffnesses. The influences of leakage effects on the static and dynamic stiffnesses are also discussed. Furthermore, the leakage coefficients are influenced by the eddy-current effects will further decrease the dynamic stiffnesses. The stiffnesses are also investigated by the static and transient finite-element methods (FEMs). Finally, a prototype is designed and fabricated. The FEM results and experimental results demonstrate the validity of the analysis.