Effects of actuator dynamics in active control of surge with magnetic thrust bearing actuation

Control of surge in centrifugal compressors is accomplished by modulating the clearance of the impeller with a magnetic thrust bearing. The physical mechanism exploited is the sensitivity of the centrifugal compressor characteristic to the tip clearance of the unshrouded impeller. A nonlinear tip clearance controller is designed using backstepping. The controller is designed with the objective that system trajectories remain on the compressor characteristic curve which ensures zero steady state offset of the impeller and maintains the efficiency of the compressor. Special attention is paid to the dynamic effects of the actuator, which is included explicitly in the control synthesis. Results from simulations of the nonlinear model for a single stage high speed centrifugal compressor show that the compressor characteristic curve can be stabilized with acceptable control authority and modest dynamic requirements