Control of a smart electro-magnetic actuator journal integrated bearing to a common equilibrium position: A simulation study

Abstract

The integration of plain journal bearings (JBs) and active magnetic bearings (AMBs) has previously been introduced as an innovative bearing concept in rotating machinery, known as smart electro-magnetic actuator journal integrated bearings (SEMAJIBs). The integrated bearing system tends to exploit the advantages and eliminate the deficiencies of each individual bearing technology. However, the integration of the two bearing technologies introduces new design and control challenges, such as operating the two bearings at a common equilibrium position. The mismatch between the equilibrium positions of the two bearings consumes both bearing load capacities leading to a load sharing problem. A novel experimentally validated control scheme has been adopted in this study to eliminate this problem and to ensure the availability of the integrated bearing load capacities. The scheme introduces a low frequency periodic biasing that enables the controller to detect non-zero static force in the AMB by sensing rotor motion at the bias carrier frequency. Consequently, the AMB controller can modify its magnetic center to match the JB equilibrium position resulting in zero static force in the AMB. Additionally, the control scheme permits the conventional control of AMBs to overcome JBs instabilities. The effectiveness of the control scheme has been demonstrated through numerical simulations using a Jeffcott rotor model supported on a pair of SEMAJIBs, for both stable and unstable operating regimes of the rotor.