NONLINEAR CONTROL OF SURGE IN AXIAL-COMPRESSION SYSTEMS

This paper discusses the nonlinear control of surge in axial compressi on systems. A nonlinear model-based Luenberger-type observer is first developed from a simple incompressible flow model of an axial compress or rig; then the input-output feedback Linearizing control technique i s employed to derive an appropriate control law. The use of the output observer as the basis for the control design enables the reconstructi on of approximate system states from a single output measurement, it e nhances transient tracking of measured output, and it reduces the dest abilizing effect of measurement noise in closed loop. The nonlinear co ntroller described in this work achieves an implicit linearization of the dynamics between the measured output variable, the dynamic pressur e at the compressor inlet and the system input variable (the throttle area parameter). The designed controller is validated by both simulati on and experimental demonstration on an axial compressor experimental rig. The controlled system responses show adequate stabilization of th e surge dynamics in the presence of impulsive persistent disturbances in system conditions. Further evaluation of the overall controlled sys tem performance is enhanced by comparisons with a linear surge control ler. It is shown that gain scheduling along nominal conditions is not required to maintain uniform closed-loop performance, during tracking of setpoint changes, with the nonlinear controller.