Stiffness Of Magnetic Bearings Research Articles

Improvement of the Static and Dynamic Characteristics of Water-Lubricated Bearings With Integrated Halbach Magnet Arrays

The generation of frictional vibration and noise by water-lubricated bearings is one of the most severe problems putting at risk the safety and concealment of ships. Here, Halbach magnet arrays were integrated as the upper bush of the water-lubricated bearing with the aim of suppressing frictional vibration. Simulations and experiments were conducted and compared between the magnetic bearing and a normal rubber bearing. Effects of magnetic strength, Halbach array length, rotational speed, and external load on bearing characteristics were analyzed. The results show superior static and dynamic performances on the magnetic bearing. More specifically, attractive forces generated by Halbach magnets can reduce static pressure by nearly 37% on the bottom bush. Stiffness of magnetic bearings was calculated as smaller than for normal bearings, indicating a lower natural frequency. Shaft trajectories were observed close to the geometric center of bearing yielding less stress concentration on the bottom bush of the magnetic bearing. Finally, test rig experiments demonstrated suppressed vibrational peaks and reduced frictional vibration (more than 10 dB) on the magnetic bearing. It is also interesting to note that the magnetic bearing even shows exceptional robustness regarding fluctuations of rotating speed or external load. This study presents a new routine for overcoming the frictional vibration and noise of water-lubricated bearings.

High-Precision Control for Magnetically Suspended Rotor of a DGMSCMG Based on Motion Separation

The magnetically suspended rotor (MSR) in a double-gimbal magnetically suspended control moment gyro (DGMSCMG) is a complicated system with multivariable, nonlinearity, and strong coupling. Not only the torsional motion of the MSR is coupled depend on the rotating speed but also its translational and torsional motions at the same axis are coupled due to the asymmetric position stiffness of magnetic bearings. Besides, the MSR also encounters the nonlinear coupling torque due to gimbals' movements. These problems influence the control accuracy of the MSR. To resolve these issues, this work presents a high-precision control strategy. A compensation method for asymmetric position stiffness is proposed to realize separation between the translational and torsional motions. Then the integral sliding mode control based on motion separation (MSISMC) is employed to stabilize the translational and torsional dynamics. To suppress the coupling torque from gimbals' movements, a novel switching function considering the estimation of the coupling torque is designed in torsional controller, and the decoupling control for the torsional motion is implemented by pole assignments. The stability of the closed-loop MSR control system is analyzed by the Lyapunov and state space methods. Comparative simulations and experiments verify the effectiveness and superiority of the proposed control strategy.

Influence of Magnetic Bearing Stiffness on Rotor in Wind Turbine Generator

Magnetic suspended wind turbine generator is widely studied due to its low loss, low maintenance cost and high reliability. However, affected by the small stiffness of magnetic bearing, the generator shaft supported by magnetic bearing will be eccentric. Therefore, the performance of generator will be affected. A horizontal axial magnetic suspended wind turbine generator is designed in this paper. The variations of shaft eccentricity and Maxwell force of rotor supported by different bearing stiffness are studied. The results show that the shaft eccentricity affects the performance of generator; and the bearing stiffness is the key to reduce those effects. The magnetic bearing designed in this paper can meet the requirements of generator.

Stiffness of Magnetic Bearings Subjected to Combined Static and Dynamic Loads

This paper investigates the stiffness of a magnetic bearing that is subjected to the combined action of static and dynamic loads. Since their sum cannot exceed the saturation load, a large static load will imply that the bearing can carry only a small dynamic load. This smaller dynamic load together with the practical vibration amplitude define a practical upper bound to the dynamic stiffness. This paper also presents approximate design formulas and curves for this stiffness capacity as a function of the ratio of dynamic and static loads. In addition, it indicates that vibrations larger than a certain gap fraction can destabilize the magnetic bearing. This gap fraction, called the critical gap fraction, depends on the dynamic and static load ratio. For example, if the dynamic load is half of the static load, the use of more than 25 percent of gap can destabilize the bearing.