Extended Nonlinear Dynamic Inversion Control Laws for Unmanned Air Vehicles

Abstract

This paper presents a novel configuration for guidance and tracking control laws for unmanned air vehicles (UAV) based on an extended nonlinear dynamic inversion (NLDI) approach. Current outer/inner loop architectures use dynamic inversion for the outer loop controller while using linear compensation-type control for inner loops. That design, although it performs well at nominal conditions, lacks robustness under certain upset flight conditions. The design proposed in this paper includes inner and outer loop control modules that both rely on the use of an NLDI control scheme. The main objective of the control laws is to minimize forward, lateral, and vertical distances with respect to a desired trajectory, and maintain stability and adequate performance in the presence of sub-system failures and upset environmental conditions. The implementation of this control laws scheme is illustrated through a simulation example using a mathematical model of the West Virginia University (WVU) YF-22 UAV. The performance of the control laws is evaluated during autonomous flight in terms of trajectory tracking errors and control activity at nominal and abnormal conditions including actuator and sensor failures and excessive turbulence. The results obtained with the WVU UAV simulation environment show that for all cases investigated the extended NLDI approach has desirable fault tolerant capabilities.