Design of control law for rotating stall subject to actuator constraints

Presented in this paper is an analytical study of the closed-loop stability of rotating stall control in an axial flow compressor subject to a nonlinear spatial actuation constraint. To account for the actuator constraints during the design, the problem is formulated as an absolute stability problem for a linearized spatial domain model of an axial flow compressor in series with the saturation element. In particular, the circle criterion is extended to accommodate the complex nature of the spatial domain. A graphical interpretation of the circle criterion results, which allows classical control design techniques to be used in the design of the gain and phase for a complex gain control law that increases the region of absolute stability guaranteed by this closed-loop system-stability criteria. This allows for the actuator constraints to be accounted for during the design using classical control techniques. A comparison of the estimated domain of attraction from the circle criterion and the domain of attraction obtained through simulation of the full nonlinear compressor model are presented.