Position tracking and path following for flight vehicles using nonlinear control

This dissertation contributes to the subject of position tracking and path following for nonlinear non-minimum phase flight vehicle models. We show that the non-minimum phase property for the class of control objectives studied in this dissertation results from inherent coupling between the aerodynamic control moments and the aerodynamic control forces that are used to control the flight vehicle. We demonstrate that the solution of the non-minimum phase flight control problem depends on the class of output commands (desired trajectories or maneuvers). We develop procedures for designing nonlinear controllers for the class of trimmed, near trimmed and aggressive commands.; The flight control problem is solved by first converting the flight models into normal form error coordinates; then we identify a state partition that leads to a decomposition of the original non-minimum phase model into two parts: a minimum phase part with trivial zero dynamic and a non-minimum phase part. For the class of trimmed and near trimmed trajectory tracking commands, the resulting tracking controller is a nonlinear static state feedback. We present robustness inequalities for the class of near trimmed commands to provide trade-off between internal stability and tracking performance. For the class of aggressive trajectory tracking commands, a non-causal feedforward control is added to the static feedback control to achieve asymptotic trajectory tracking.; We show that use of feedforward control is essential to achieve good tracking performance when dealing with non-minimum phase systems. We also study an alternative nonlinear control design for flight control problems, using the maneuver regulation approach. The maneuver regulation controller regulates the position errors transverse to the desired path and the velocity errors along the desired path but not the position errors along the desired path. To construct maneuver regulation controllers first an output tracking controller is designed that guarantees local uniformly asymptotic trajectory tracking. Next the output tracking controller is converted to a maneuver regulation controller using an on-line solution of a minimization problem. We show through simulations that the maneuver regulation design leads to a larger domain of attraction, smaller control signals and robustness to external disturbances. The various control approaches are illustrated by several flight vehicle models that are intended to track specific output commands.