Adaptive Sliding Mode 3-D Trajecotory Control of F/A-18 Model Via SDU Decomposition

Abstract

The paper treats the design of (i) a variable structure control (VSC) system and (ii) an adaptive variable structure control (AVSC) system for three-dimensional trajectory control of a simplifled F/A-18 model in the in presence of parametric uncertainties. For the nonlinear aircraft model, it is assumed that the high-frequency gain matrix associated with the rotational dynamics is not known. The VSC and AVSC control systems have a variable structure outer feedback loop, designed using sliding mode control technique. The outer loop design accomplishes three-dimensional (3-D (x,y,z) position) trajectory tracking using angular velocity vector (p,q,r) as virtual control input and the derivative of the thrust. Then using a backstepping technique, the inner loop is designed to produce required angular rates of the aircraft using aileron, rudder, and elevator control surfaces. The VSC and AVSC control systems include a variable structure inner loop and an adaptive inner feedback loop, respectively. For inner loop design, SDU decomposition of the input matrix is used, yielding singularity free adaptive control law and VSC law with relaxed constraints on the input matrix uncertainties. It is shown that in the closed-loop VSC and AVSC control systems, asymptotic trajectory tracking is accomplished. Simulation results for 180 ‐ climbing turn and helical path following are presented, which show accurate 3-D trajectory tracking performance in spite of large parameteric uncertainties.