Unmanned Aerial Vehicles: Embedded Control

Chapter 2

Nested Saturation Control for Stabilizing the PVTOL Aircraft ¹

2.1. Introduction

Within the research activities on the aerial vehicle control, we have been particularly interested in the PVTOL aircraft model for several reasons. The planar vertical take-off and landing (PVTOL) aircraft system is indeed based on a simplified real aircraft model which possesses a minimal number of states and inputs but which retains the main features that must be considered when designing control laws for a real aircraft. It also serves as a support for researchers interested in helicopter aerodynamics, because it represents a simplified mathematical model of a helicopter. It then represents a good test-bed for researchers, teachers and students working on flying vehicles.

Let us recall that the PVTOL aircraft system is an underactuated system, since it possesses two inputs u₁, u₂ and three degrees of freedom [x, y, θ] (see equations (2.1)), and it moves on a plane (see Figure 2.1). The PVTOL aircraft is composed of two independent motors which produce a force and a moment on the vehicle. The main thrust is the sum of each motor thrust. The roll moment is obtained by the difference of motor’s angular velocities.

The control of the PVTOL aircraft represents a real challenge because of its simplicity, its nonlinear nature and its particular properties. Indeed, the system has a nonminimum phase as the linearized system possesses an unstable zero dynamic because of the coupling between the ...