Robust fractional-order sliding mode tracker for quad-rotor UAVs: Event-triggered adaptive backstepping approach under disturbance and uncertainty

Abstract

In this paper, tracking control of the quad-rotor UAVs in the presence of exterior perturbations and dynamical uncertainties is accomplished using an event-triggered adaptive backstepping fractional-order sliding mode control scheme. For this reason, tracking errors are considered as the difference between the actual and desired states of the quad-rotor system. Moreover, event-triggering errors are defined as the difference between tracking errors at time ti and tracking errors at time t. Afterward, a dynamical model of the quad-rotor system under external disturbance and model uncertainty is obtained based on the tracking errors’ states. Then, the fractional-order sliding mode surface based on the tracking errors and virtual control inputs is proposed to guarantee the convergence of desired tracking errors. Hence, to avoid the complexity in the control process, the virtual control inputs are presented as fractional-order integral-type laws to avoid high derivatives of virtual control inputs. In addition, the event-triggering condition is applied for backstepping fractional-order sliding mode control to prevent frequent periodic action of control inputs. Moreover, employing the backstepping control procedure and the Lyapunov stability concept, the convergence of fractional-order sliding surfaces is guaranteed. Later, the fractional-order adaptive laws are designed to estimate the unknown upper bounds of perturbations and uncertainties. Finally, to demonstrate the efficiency of the control algorithm recommended in this paper, the simulation results on MATLAB/Simulink environment are presented. A comparison between the control method in this paper and another existing technique is prepared to prove the productivity of performance of the offered control method on the quad-rotor system.