Output-Feedback Stabilization of the PVTOL Aircraft System Based on an Exact Differentiator

An output-feedback control strategy for the regulation of a planar vertical take-off and landing aircraft is presented here. The strategy consists of two controllers that work simultaneously. The first controller stabilizes the vertical variable, and is based on a simple feedback-linearization procedure, in combination with a nonlinear controller (which behaves as a terminal slide mode). The other controller stabilizes the horizontal and angular variables to the desired rest position, and was designed using an energy-control method. The velocities were exactly estimated with a second-order sliding-mode observer. Because this observer computes the velocities in finite time, the control strategy can be designed independently. The effectiveness of the closed-loop system was tested through numerical simulations and compared with other control strategies.