Analytical Design and Stability Analysis of the Universal Integral Regulator Applied in Flight Control

This paper considers the analytical design and stability analysis of an output feedback flight control problem for a rigid fighter aircraft which has a highly nonlinear dynamic. In this paper, a robust technique known as Universal Integral Regulator (UIR) has been chosen to solve the tracking problem due to the possibility to demonstrate the stability of the system and analytically compute the control parameters. The UIR is a combination of Continuous Sliding Mode Control (CSMC) and a Conditional Integrator (CI) which provides integral action only inside the boundary layer, enhancing the transient response of the system and providing an equilibrium point where the tracking error is zero. The general procedure consists firstly of rewriting the aircraft dynamics in the control-affine form, then the relative degree of the system is computed and the system is transformed to normal form. An output feedback controller using a CSMC controller is proposed, and a sliding surface considering a CI is designed. The controller parameters are designed analytically, taking into account two approaches. The first approach does not consider uncertain parameters and the second one treats a stability derivative as a parametric uncertainty. Simulations were performed in order to validate the design procedure of the control technique and to demonstrate the robustness of the UIR. Detailed step by step information about the computing of the controller parameters was done and an analytical analysis of stability was developed to demonstrate the convergence of the sliding surface, conditional integrator and tracking error dynamics.