Sliding Mode Controller For Active Control Of Surge In Centrifugal Compressors With Magnetic Thrust Bearing Actuation

A new method for active control of surge in unshrouded centrifugal compressors is developed using a magnetic thrust bearing to modulate the impeller tip clearance. Use of a sliding mode control method ensures that the system trajectories remain on the steady state compressor characteristic for a significantly extended operating range beyond the compressor surge point. The actuator authority required by this action is demonstrated to be well within expected capacities. Using a simulation based on the Greitzer model with adaptations, the stable mass flow rate was reduced from 0.5 kg/sec to 0.2 kg/sec.