Active control of rotating stall in compressors
Presented in this manuscript is an investigation of active control of rotating stall in compressors. A Moore-Greitzer compressor model modified to include an array of air injectors for actuation is used to perform the study. The first study in the investigation is the design of a control law in the spatial domain to regulate rotating stall. The controller design is executed in two primary phases. In the first phase, spatial domain input-output frequency responses are obtained to facilitate the controller design process. In the second phase, feedback regulator control theory is applied resulting in the design of a complex gain controller that extends the operating range of the compressor. In the second study of this investigation, the effect of actuator saturation defined in the spatial domain is examined. Absolute stability of the rotating stall control system is investigated by applying the circle criterion to 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. Resulting is a graphical interpretation of the circle criterion which facilitates 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. The final part of the study considers the control of a variable wheel speed compressor model. A gain scheduling approach is utilized to control rotating stall during wheel speed transients. The wheel speed is chosen to parameterize the operating range for the gain scheduled controller. Local controllers are then designed at selected wheel speeds in the operating range. The resulting family of controllers are interpolated giving the gain scheduled control law. The control is shown to expand the stability region of the compressor subject to wheel speed transients. ^
Major Professors: Matthew A. Franchek, Purdue University, Sanford Fleeter, Purdue University.