| The useful range of operation in axial flow compressors is limited by aerodynamic flow instabilities such as rotating stall. Feedback control has been pursued to address the rotating stall problem in axial flow compressors in order to extend the stable operating range and to improve engine performance. These controllers guarantee the stability of the bifurcated operating solution near the stall point. However, how robust these controllers could be is still not clear. In this thesis, after presenting an introduction to the problem and providing the mathematical background of bifurcated systems and bifurcation stabilization, local robust analysis is applied systematically to evaluate feedback control design for rotating stall. Different combinations of perturbation in the system model have been considered. In particular, the set of admissible uncertainty is characterized analytically in terms of feedback control gain so that it is possible to compare the robustness of controllers with different feedback gains. We are then able to use this knowledge as a selection criteria to choose a more robust controller from a set of existing control laws. The nonlinear feedback controller is also studied for any possible advantage over the linear control laws. |
