Backstepping for Active Control of Surge in Unshrouded Centrifugal Compressors With Magnetic Thrust Bearing Actuation

Abstract

The backstepping method is applied to design a controller which is capable of actively suppressing the oscillations induced by compressor surge using the sensitivity of the centrifugal compressor characteristic to the tip clearance of the unshrouded impeller. This is achieved using a magnetic thrust bearing to modulate the tip clearance of the impeller. The controller is designed with the objective that system trajectories remain on the compressor characteristic curve in the presence of disturbances downstream of the compressor. This ensures zero steady state offset of the impeller, which maintains the efficiency of the compressor. Results from simulation of the nonlinear model for a single stage high speed centrifugal compressor show that using backstepping control, mass flow and pressure oscillations associated with compressor surge are quickly suppressed with acceptable control requirements of typical machines. Further, the stable region of the compressor operation is significantly increased and the compression system will not enter surge cycles for a wide variety of disturbances downstream of the compressor.