A review of methods for input/output selection <s> Flight control <s> Recent work has shown that compression systems can be actively stabilized against the instability known as surge, thereby realizing a significant gain in system mass flow range. Ideally, this surge stabilization requires only a single sensor and a single actuator connected by a suitable control law. Almost all research to date has been aimed at proof of concept studies of this technique, using various actuators and sensor combinations. In contrast, the work reported herein can be regarded as a step towards developing active control into a practical technique. In this context, the paper presents the first systematic definition of the influence of sensor and actuator selection on increasing the range of stabilized compressor performance. The results show that proper choice of sensor as well as actuator crucially affects the ability to stabilize these systems, and that, overall, those actuators which are most closely coupled to the compressor (as opposed to the plenum or throttle) appear most effective. In addition, the source of the disturbances driving the system (for example, unsteady compressor pressure rise or unsteady combustor heat release) has a strong influence on control effectiveness, as would be expected for a controls problem of this type. This paper both delineates general methodologies for the evaluation of active compressor stabilization strategies and quantifies the performance of several approaches which might be implemented in gas turbine engines.Copyright © 1992 by ASME <s> BIB001 </s> A review of methods for input/output selection <s> Flight control <s> A theoretical study has been conducted to determine the influence of actuator and sensor choice on active control of rotating stall in axial-flow compressors. The sensors are used to detect small amplitude traveling waves that have been observed at the inception of rotating stall in several different compressors. Control is achieved by feeding the sensed quantity back to the actuator with a suitable gain and spatial phase shift relative to the measured wave. Actuators using circumferential arrays of jets, intake ports, and movable inlet guide vanes upstream of the compressor, and valves downstream of the compressor were considered. The effect of axial velocity, static pressure, or total pressure measurement on control effectiveness was investigated. In addition, the influence of the actuator bandwidth on the performance of the controlled system was determined. The results of the study indicate that the potential for active control of rotating stall is greater than that achieved thus far with movable inlet guide vanes. Furthermore, axial velocity sensing was most effective. Actuator bandwidth affected the performance of the controlled compressors significantly, but certain actuators were affected less severely than others. <s> BIB002
Specialized IO selection methods have also been used for aircraft and spacecraft control purposes. There is no method that is clearly used the most frequently. Based on the complexity and the nature of the control problem, the preferred IO selection method should be considered for each application separately. For a process-control-like problem (e.g., controlling #uids, temperatures, and pressures in engines) IO controllability measures are a suitable starting point, whereas state controllability and observability and e$ciency of manipulation and estimation may be preferred for mechanical structures (e.g., active vibration control of wings and antennas). The following applications of #ight control are encountered: Hoskin et al. (1991, combined RS and NP) , Reeves (1991, Section 7.2, combined RS and NP) , and Samar and Postlethwaite (1994, state controllability and observability, RHP zeros, IO controllability) determine suitable actuators and sensors for controlling highperformance aircraft engines. E Compressors are often used in aircraft engines and, in this context, IO selection for compression systems could also be mentioned, see BIB002 , Montazeri-Gh, Allerton, and Elder (1996, e$ciency of manipulation and estimation), BIB001 , and Van de Wal et al. (1997, combined RS and NP) . E The optimal location of actuators for attitude control of satellites is considered by MuK ller and Weber (1972, state controllability and observability).