Robust control of a surge and rotating stall in an axial compressor

Abstract

This thesis presents an investigation of the stability of axial compression systems when external disturbances are introduced. Aerodynamic stability is considered from a nonlinear perspective. From this perspective, the goal is to enhance the ability of compressor systems to remain stable in the face of external disturbances. Experiments were conducted on a low-speed three-stage axial compressor. Instead of achieving extension of linearly stable operating range, this research is focused on the followings: (1). The operability of the compressor, the ability of maintaining the stable operations of the compressor near the operating points in the presence of the external disturbances, was considered. The concept of domain of attraction was adopted to characterize the operability or the disturbance rejection of the compressor. An experimental method was developed to generate disturbances and measure the approximate domain of attraction in terms of the zeroth and first mode flow perturbations. (2). Improvement of the approximate domain of attraction was demonstrated by active control. Both the constant gain control which has been used in many range extension tests and the sliding mode control which is model based, doubles the maximum allowable amplitudes of the zeroth and first mode flow perturbations. (3). The downstream bleed was chosen as the actuation, which is easy to implement and more practical. The number of the bleed valves was chosen to be four to compromise the goal of reducing the number of actuators and the requirement of achieving a satisfactory control effectiveness. (4). The domain of attraction was also examined under inlet distortions. The nonlinear simulation showed that the disturbance rejection of the compressor with background distorted flow was improved by active control.