Nonlinear control designs for systems with bifurcations with applications to stabilization and control of compressors

This paper studies the effects of applying both nonlinear feedback and time-varying control algorithms in the form of inlet flow disturbances by introducing variations in the shut-off head of a single stage axial compressor. The closed loop controller utilizes nonlinear feedback in order to stabilize rotating stall. Using bifurcation analysis, it is possible to analytically guarantee stability of local bifurcated solutions near the stall point. Physically, this means that the system will no longer “jump” to a large amplitude oscillatory mode when bifurcating at the stall point. Thus the possible operating region of the axial compressor is enlarged. The open loop control strategy provides oscillatory input to the shut-off head coefficient. For some model systems, this type of strategy is shown to be effective in enhancing stability margins and improving efficiency. Methods of implementing both types of control laws using variations inlet guide vanes and bleed valves and by blowing air into the compressor are under investigation