Analysis and active control of stall instabilities in axial flow compressors are pursued using a combination of bifurcation analysis and nonlinear control. A low-order discretization model of a PDE compressor model is found to exhibit a stationary (pitchfork) bifurcation at the onset of stall. Using ID throttle opening (e.g. bleed valve) as a control, analysis of the linearized system at stall shows that the critical mode (zero eigenvalue) is unaffected by linear feedback. Hence, nonlinear stabilization techniques are necessary. A quadratic feedback control law is proposed based on the lower-order model and is found to adequately Serve the control purposes for both tile lower order and higher order discretizations.
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