Active Control Of Surge In Centrifual Compressors By Magnetic Actuation

Surge is a kind of unstable state that happens on fluid machineries like compressors and blowers when the flow rate decreases to a limit value.And surge can cause serious damage to the equipment.This research presents a method for active surge control using active magnetic thrust bearing as actuator to change the impeller tip clearance to suppress surge.This surge control method has advantages that no need of additional hardware,broadening the scope of stable operation,fast response and no efficiency loss.Firstly the established model for the dynamics of the compressor system was extended to include the influence of dynamic tip clearance modulation.In order to reduce the difficulty of controller design,the tip clearance effect equation and the whole system model were linearized.The linearization error was proved to be acceptable.Secondly a surge controller based on mass flow feedback was developed.Results from simulation of the compressor system model with the controller showed the control effect of this the control strategy and the weaknesses that susceptible to the influence of the actuator dynamic limitations.In view of this weakness,a PID controller was developed.Simulation results showed that this controller can improve the control effect with the influence of the actuator dynamic limitations.For the weakness of mass flow rate measurement,an extended Kalman filter(EKF)was designed to estimate the mass flow rate from the measured compressor pressure.The simulation of the pressure output feedback control built by combining the PID control and EKF proved the effectiveness of the pressure feedback controller with EKF.Finally,another PID controller for magnetic thrust bearing suspension was designed.The large axial displacement of rotor for surge control introduces parametric variation.A H? robust controller was developed to increase the system robustness.Position tracking experiment and tability experiments in different locations with PID controller and with H? were carried out.Results of position tracking experiment showed the smaller position signal tracking error H?controller has than PID controller.And suspension stability experiments in different locations showed that the position offset distance with H? controller is larger than with PID controller,but the oscillation with H? controller in the process of recovery is smaller than with PID controller.And both H? control and PID control can satisfy the needs of surge control.