Effect of sinusoidal base motion on a magnetic bearing

Many of the proposed applications for magnetic bearings involve their use in moving vehicles. These include flywheels for energy storage in terrestrial applications, such as buses and trains, and also in space-based applications, such as satellites. Most of the existing research literature on magnetic bearings is for static systems where the base is stationary. For vehicular applications, magnetic bearings will be subject to base motion that will have significant effects on the dynamics. In addition, magnetic bearings designed for vehicle use are expected to be power-limited, which leads to decreased stiffness and damping. The implications of these effects on the design of active magnetic bearing systems are significant but have not been fully investigated. In order to address the base motion scenario, a small non-rotating test rig with a single magnetic bearing mounted on a shaker has been built and tested to study the effect of sinusoidal base motion on the magnetic bearing's ability to support a target mass. The tests include base excitation of the system at different frequencies and amplitudes including the natural frequency of the system. Results from this test rig for three cases of bearing stiffness and damping properties are presented. Test results show both linear and non-linear behavior for the cases of bearing stiffness and damping tested. The tests also demonstrate the implications associated with the requested level of stiffness and damping on limiting the operating performance range of the magnetic bearing undergoing sinusoidal base motion.