Active Surge Control for Magnetically Suspended Centrifugal Compressors Using a Variable Equilibrium Point Approach

Surge is one of the main rotor dynamic instabilities limiting the operation of centrifugal compressors. This paper proposes an active surge control scheme for magnetically suspended centrifugal compressors using a variable equilibrium point approach. Multiple uncertainties caused by magnetic air gap adjustment are considered for the active magnetic bearing (AMB) control systems. By using the combination of an analytical model and a finite-element method, the perturbation of bearing force parameters, including the force-current factor and the force-displacement factor, is analyzed. The model uncertainties caused by the perturbation of the power amplifier parameters are identified through the online frequency sweep excitation. Based on the uncertainty analysis of the AMB control system, a μ-synthesis-based controller is designed for the axial magnetic bearing system to suppress the vibration caused by surge. The experiments demonstrate that the proposed method can suppress surge and improve the reliability of the system by using automatic magnetic air gap adjustment of the AMB-rotor system.