Inverse Optimal and Theta-D Control based near Optimal flight controller

Abstract

The objective of this paper is to present a nonlinear flight control strategy, recommendable for the entire flight regime. Traditional controllers exhibit innate performance deficiencies in the widely varying aerodynamic scenario with substantially elevated control efforts. Therefore nonlinear optimality based control would be vital for the overall system performance. The prime feature of Inverse Optimal Control is that it guarantees asymptotic stability and optimality, globally, with respect to a performance index determined posteriori. The basis of Inverse Optimal control (IOC) rests on the formulation of an appropriate Control Lyapunov Function (CLF), the determination of which is in fact laborious in most cases. However here, the determination of CLF, for a particular class of nonlinear systems, is systematized to some extent. The 6 DOF aircraft dynamics separated into two timescales is considered for simulation study. The slow angular dynamics of the outer loop is controlled via Inverse Optimal Control. A suboptimal Theta-D controller is employed for the control of the fast inner loop. Thus in effect a near optimal control performance is expected of the resultant nonlinear control system. The inherent stability and robustness characteristic of the participating control laws will contribute the same to the overall system. Simulation results verify all the anticipated capabilities in terms of performance, optimality, stability and robustness.