Dynamic Characterization of Electrodynamic Bearings Combined with Active Magnetic Dampers

Electrodynamic Bearings (EDBs) are a kind of passive magnetic bearings that exploits the interaction between the eddy currents in a rotating conductor and the stationary magnetic field to provide restoring forces. They have been regarded as an appealing alternative to Active Magnetic Bearings (AMBs), having the possibility to obtain stable levitation using standard conductive materials at room temperature without introducing negative stiffness in any direction. Compared to AMBs, EDBs present advantages such as lower cost, higher reliability due to simplicity of configurations. However, applications of EDBs are still limited due to instability issues. The rotating damping force arising in EDBs causes unstable behavior of the rotor, which requires a stabilizing solution. A hybrid solution is presented in the present paper, where Active Magnetic Dampers (AMDs) are applied to provide non-rotating damping to the rotor supported by EDBs to obtain stable operation. This solution is designed to exploit the high reliability of EDBs, overcoming the stability problem by means of controllable AMDs. Rather than using active electromagnetic actuators to provide stiffness (like in standard AMBs), the AMBs here are used as dampers only (thus called AMDs), resulting in downsized and more efficient AMBs. The effect of the EDB−AMD system has been studied both analytically and experimentally. A dedicated test rig has been built to validate the analytical model and to characterize the system. Dynamic characterization of the system is presented, demonstrating the effectiveness of this solution and dynamics of the system.