Control Design of an Unstable Non-Minimum Phase Aircraft Subject to Control Surface Saturation

摘要

This thesis seeks to validate a design technique for the control of unstable aircraft which are subject to limited control authority. It applies the technique to a realistic aircraft model, instead of the simplified models used in the theoretical development, to produce a pitch rate controller for widely spaced regions of the flight envelope. First the aircraft is stabilized by feeding back pitch rate. Then an adjustable command limiter is placed in the input path for the stable effective plant. The saturation level of the limiter, adjusted by a second feedback loop, provides the proper command tracking response when the command limiter is not saturated. The final element is a minor feedback loop around the command limiter to provide a second degree of freedom to ensure the limiter comes out of saturation as quickly as possible. Simulations for step commands ranging from 1 to 5 deg/sec pitch rate show the design is quite successful. The stabilator does not saturate in a manner which causes instability even when responding to extreme commands. Simulations of a pulse command show that the command limiter unsaturates rapidly and the aircraft responds appropriately to a reduced pitch command even when the stabilator is near the limit. The technique applies relatively simple linear design tools to the nonlinear problem of control surface saturation. Keywords: Attitude control systems; Stabilization systems; Computer aided design; Pitch motion; Aerodynamic control surfaces; Electrical engineering. (EDC)