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An adaptive sliding mode fault‐tolerant control strategy is proposed for a quadrotor unmanned aerial vehicle in this article to accommodate actuator faults and model uncertainties. First, a new reaching law is proposed, with which a sliding mode control (SMC) law is constructed. The proposed reaching law is made up of a sliding variable and the distance between it and a designated boundary layer, and it can effectively suppress the unexpected control chattering while preserving the necessary system tracking performance. Then, an adaptive SMC scheme is proposed to further solve the fault and uncertainty compensation problem. The proposed adaptation law helps to prevent overestimation of the adaptive control parameters, as well as avoiding control chattering. Finally, a number of comparative simulation tests are carried out to validate the effectiveness and superiority of the proposed control strategy. The demonstrated quantitative comparison results confirm its advantages. [ABSTRACT FROM AUTHOR]

This paper considers the reliable control problem for multiple trailing fixed-wing unmanned aerial vehicles (UAVs) against actuator faults and wake vortices. A distributed adaptive fault-tolerant control (FTC) scheme is proposed by using a distributed sliding-mode estimator, dynamic surface control architecture, neural networks, and disturbance observers. The proposed control scheme can make all trailing fixed-wing UAVs converge to the leading UAV with pre-defined time-varying relative positions even when all trailing UAVs encounter the wake vortices generated by the leading UAV and a portion of trailing UAVs is subjected to the actuator faults. It is shown that under the proposed distributed FTC scheme, the tracking errors of all trailing UAVs with respect to their desired positions are bounded. Comparative simulation results are provided to illustrate the effectiveness of the proposed control scheme. • The fault-tolerant close formation flight control of multiple UAVs is considered. • The nonlinear 6-DOF fixed-wing UAV model is used in the control design. • A composite learning algorithm is proposed to enhance the estimation capability. [ABSTRACT FROM AUTHOR]

This paper investigates a difficult problem of distributed fault-tolerant cooperative control for multiple unmanned aerial vehicles (UAVs) in the presence of actuator faults and input saturation. To eliminate the “explosion of complexity” in the traditional backstepping architecture, the dynamic surface control is utilized to construct the distributed fault-tolerant control scheme. Moreover, by using the disturbance observer technique, actuator faults and external disturbances are estimated as lumped uncertainties. Furthermore, to reduce the adverse influence caused by the control input saturation of UAVs, auxiliary dynamic systems are introduced to regulate the control signals when the input signals are saturated for a long time. The key feature is that the proposed fault-tolerant cooperative controller is designed based on the local information of neighboring UAVs and the factors including actuator faults, input saturation, and external disturbances are simultaneously addressed. It is shown by Lyapunov approach and graph theory that the synchronization tracking stability can be guaranteed and all follower UAVs can track the leader UAV. The effectiveness of the proposed control scheme is further validated by numerical simulation results. [ABSTRACT FROM AUTHOR]

This paper investigates the distributed fault-tolerant containment control (FTCC) of multiple unmanned aerial vehicles (multi-UAVs) when a subset of multi-UAVs is encountered by actuator faults and input saturation. The topology involving multiple follower UAVs and leader UAVs is an undirected, fixed communication network and only a subset of follower UAVs has access to the leader UAVs. By the combination of graph theory and sliding-mode observer (SMO), the desired reference of each follower is first estimated in a distributed manner. Then, by utilizing the estimated knowledge, a set of distributed control laws is iteratively designed to steer follower UAVs into the convex hull spanned by the leader UAVs. In the distributed control scheme, disturbance observer (DO) technique is used to estimate unknown lumped uncertainty including external disturbances and actuator faults. An auxiliary dynamic system is constructed to compensate the input saturation. Moreover, to eliminate the "explosion of complexity" in traditional backstepping architecture, high-gain observer (HGO) technique is integrated into the backstepping architecture to estimate the virtual control signals and their first derivatives. Furthermore, by using graph theory and Lyapunov-based approach, it is shown that the distributed fault-tolerant containment controller can guarantee all follower UAVs to converge into the convex hull spanned by all leader UAVs. Finally, numerical simulations are presented to demonstrate the effectiveness of the proposed distributed control scheme. [ABSTRACT FROM AUTHOR]

Highlights • This paper explores the adaptive fault-tolerant control of quadrotor helicopters. • Actuator faults, parametric uncertainties, and disturbances can be all compensated. • With the aid of proposed adaptive schemes, control chattering problem is avoided. Abstract This paper presents a disturbance observer-based adaptive sliding mode control (SMC) strategy for a quadrotor helicopter subject to multiple actuator faults, parametric uncertainties, and external disturbances. Unlike most of the existing control strategies for quadrotor helicopters, actuator faults, parametric uncertainties, and external disturbances can be simultaneously compensated within the proposed control scheme. Firstly, by employing the adaptive control parameters in both continuous and discontinuous control parts, the proposed control strategy can generate appropriate control signals to accommodate actuator faults and parametric uncertainties without merely relying on the robust discontinuous control strategy of SMC. Then, a nonlinear disturbance observer is designed and integrated to attenuate external disturbances while keeping the small value of the discontinuous control gain of SMC. In addition, the stability analysis of the proposed control strategy is given, showing that the presented controller can ensure system tracking performance and make the tracking errors arbitrarily small under the concerned situation. The effectiveness of the proposed control strategy is demonstrated through comparative numerical simulations and experimental tests of a quadrotor helicopter under different faulty and uncertain scenarios. [ABSTRACT FROM AUTHOR]

This paper presents a dual adaptive fault-tolerant control strategy for a quadrotor helicopter based on adaptive sliding mode control and adaptive boundary layer. Within the proposed adaptive control strategy, both model uncertainties and actuator faults can be compensated without the knowledge of the uncertainty bounds and fault information. By virtue of the proposed adaptive control scheme, the minimum discontinuous control gain is adopted, which significantly reduces the control chattering effect. As compared to the existing adaptive sliding mode control schemes in the literature, larger actuator faults can be tolerated by employing the proposed control scheme while suppressing control chattering. Moreover, boundary layer is used to smoothen control discontinuity and further eliminate control chattering. Nevertheless, the choice of boundary layer thickness is a trade-off between system stability and tracking accuracy. By explicitly considering this fact, an adaptive boundary layer is developed and synthesized with the proposed adaptive control framework to ensure stability and tracking accuracy of the considered system. When the control parameter tends to be overestimated, the thickness of boundary layer can be appropriately adjusted to avoid control parameter overestimation. Simulation and experimental tests of a quadrotor helicopter are both conducted to validate the effectiveness of the proposed control scheme. Its advantages are demonstrated in comparison with a conventional adaptive sliding mode control scheme. [ABSTRACT FROM AUTHOR]