APPLICATION OF APPROXIMATE I O LINEARIZATION TO AIRCRAFT FLIGHT CONTROL/

This paper examines the performance enhancement of a statically unstab le aircraft subject to the input and state constraints. Under control saturation, i/o linearizability is destroyed and the state trajectorie s may not be attracted to the sliding surface. If the reference signal s are sufficiently large and the zero-dynamics is lightly damped, the i/o linearizing control may become unreasonably large in magnitude, ma king the closed-loop system susceptible to the damaging effects of con trol saturation. In addition to performance degradations such as incre ased tracking errors, control saturation can drive the closed-loop sys tem to instability. In this paper, a new design method called approxim ate i/o linearization is presented to enhance the performance of the S ISO longitudinal flight control problem under saturation. The new appr oximate i/o linearization law is obtained by solving a pointwise minim ization problem. The function to be minimized consists of a surface wh ose relative degree is one, its derivative, and weighted square of the input u. The advantages of the approximate i/o linearization is that the adverse effects of control saturation can be minimized by properly selecting the weight on the usage of the control. The only requiremen t for the new technique is that the original plant be locally i/o line arizable. Thus approximate i/o linearization does not impose additiona l strict requirements on the plant. In the remaining sections of the p aper, stability and bounded tracking properties of the approximate i/o linearization are proven. Finally, a longitudinal flight control prob lem is used to demonstrate the application of approximate i/o lineariz ation.