The main contribution of the paper is to propose a scheme of attitude controller for a class of unmanned aerial vehicles based on an adaptive version of the super-twisting algorithm. This controller is based on a very recent second-order sliding mode controller, which is robust in spite of uncertainties and perturbations, ensures finite time convergence, reduces the chattering, increases the accuracy, and does not require time derivative of the sliding variable. A very important feature of the controller is its adaptive gain, which allows to design the controller without knowing bounds of the uncertainties and perturbations. This controller is validated by experimental results. Comparisons versus PID-based controller are made in order to evaluate the robustness of the closed-loop system when similar perturbations are acting.
1479has been initially developed in [11] and used in [12, 13]: it allows to decouple the system thanks to the introduction of both virtual inputs for travel and elevation angles and to design a desired reference for the pitch angle. This approach is adapted to user's expectations. Indeed, in standard working conditions, the user can provide elevation and travel desired trajectories with respect to his objective, the pitch trajectory being online defined to achieve the tracking of elevation/travel desired trajectories. The controller scheme used in [11][12][13] has been modified in the current paper in order to prove the stability of the closed-loop system (which has not been formally established in the previous papers). The proposed controller is based on adaptive second-order sliding mode, which allows to obtain robust behavior with respect to modeling errors, uncertainties, and perturbations, while having reduced magnitude gain, which is dynamically adapted. It is well known that sliding mode control is robust with respect to perturbations and uncertainties and is simple to be tuned (high gain approach by considering the 'worst' case). Unfortunately, high frequency oscillations of the control input, the so-called chattering phenomenon, appear and can damage the actuators. In order to reduce this phenomenon, to improve the accuracy, and to ensure finite time convergence to the control objective, high-order sliding mode control appears at the beginning of 1990s [14], especially second-order sliding mode controllers as twisting and super-twisting (STW) algorithms. The advantage of the STW algorithm versus the twisting one is that no time derivative of the sliding variable is required, which reduces the noise in the control input. In the current paper, an adaptive version of the STW controller is used [15,16]. This adaptive algorithm allows a robust control without overestimating the control gains for a large class of nonlinear systems of relative degree 1 with bounded additive and multiplicative uncertainties perturbations whose bounds are unknown. Note that this latter feature is interesting given that it allows to reduce the identification procedure.The controller proposed in the sequel is, ...