Robust and active trajectory tracking for an autonomous helicopter under wind gust

Abstract

High levels of agility, maneuverability and the capability of operating in degraded visual environments and adverse weather conditions are the new trends of helicopter design nowadays. Helicopter flight control system should make these performance requirements achievable by improving tracking performance and disturbance rejection capability. Robustness is one of the critical issues which must be considered in the control system design for such highperformance autonomous helicopter, since any mathematical helicopter model, especially those covering large flight envelope, will unavoidably have uncertainty due to the empirical representation of aerodynamic forces and moments. The purpose of this chapter is to present the stabilization (tracking) with motion planning of a reduced-order helicopter model having 3DOF (Degrees Of Freedom) (see Fig.1). This last one represents a scale model helicopter mounted on an experimental platform. It deals with the problem of disturbance reconstruction acting on the autonomous helicopter, the disturbance consists in vertical wind gusts. The objective is to compensate these disturbances and to improve the performances of the control. Consequently, a nonlinear simple model with 3DOF of a helicopter with unknown disturbances is used. Three approaches of robust control are then compared via simulations: a robust nonlinear feedback control, an active disturbance rejection control based on a nonlinear extended state observer and a backstepping control. Design of control of autonomous flying systems has now become a very challenging area of research, as shown by a large literature (Beji & Abichou, 2005) (Frazzoli et al., 2000) (Koo & Sastry, 1998). Many previous works focus on (linear and nonlinear, robust, ...) control, including a particular attention on the analysis of the stability (Mahony & Hamel, 2004), but very few works have been made on the influence of wind gusts acting on the flying system, whereas it is a crucial problem for out-door applications, especially in urban environment: as a matter of fact, if the autonomous flying system (especially when this system is relatively slight) crosses a crossroads, it can be disturbed by wind gusts and leave its trajectory, which could be critical in a highly dense urban context. In (Martini et al., 2005) and (Martini et al., 2007a), three controllers (nonlinear,