The effectiveness of multiple UAVs at attacking the enemy target and defending against the attacking UAVs simultaneously gained researchers’ attention due to their cost efficiency and high mission success rates. This paper explores the UAV swarm vs. swarm offense/defense confrontation decision-making while attacking the aircraft carriers on open seas. The system is developed as a multi-agent system. Precisely, every UAV is modeled as an independent agent, which is free to make decisions based on the behavioral rules of the swarm, detection radius, and enemy location. A distributed auction-based algorithm with a limited data-sharing rate ability is formulated among swarm UAVs. A critical feature of the proposed strategy is that it empowers each UAV to make decisions in real-time during the mission in the presence of relatively limited communication hardware in terms of the update rate within the UAV communication system. The algorithm parameters are optimized to obtain an improved target allocation and elimination. Simulation results are presented to show the effectiveness of the proposed Offence-Defense UAV-based swarm Strategy.

This paper describes a new fault-tolerant control technique for over-actuated uncertain linear systems that compensates for actuator faults and failures using an output integral sliding mode-based control allocation strategy. An observer-based fault estimation unit is first proposed to estimate the system states and the actuator’s effectiveness level. Based on the estimated state’s information, a nominal virtual control law is created to achieve the desired specification of the perturbed system. A nonlinear output integral sliding manifold is incorporated with the nominal virtual control law that provides resilience to the closed-loop system against the uncertainty caused by the actuator’s faults and failure, states estimation error, and fault estimation error. Finally, depending on anticipated actuator efficacy from the fault estimation unit, the control allocation reroutes the virtual control input signals among the redundant actuators. A small-gain theorem is used to demonstrate the augmented closed-loop system stability. The observer and controller gains are synthesized using the linear matrix inequality technique. Finally, simulations on an aircraft system are performed to verify the efficacy of the suggested FTC technique. Compared with the existing work, the proposed approach is better able to handle actuator redundancy in faulty conditions and cater to the fault estimation error up to a certain level. Note to Practitioners —The aim of this paper is to address the reliability issues of industrial systems that contain sufficient input redundancy and are particularly designed to tolerate the faults and failures issues during the system operation. Existing fault-tolerant control schemes based on control allocations have limitations in terms of effective utilization of actuator redundancy, handling of fault estimation error, and applicability of reconfigurable control law. In this paper, we developed a fault-tolerant control strategy that is capable of addressing all the aforementioned concerns. The output integral sliding mode control-based control allocation scheme, proposed in this paper, is applicable to the class of over-actuated systems. The reconfiguration of fault-tolerant control law based on the estimated states and fault information is capable to cover a wider class of faults and failures while maintaining robustness against the system dynamics and uncertainty. The control reconfiguration is equally applicable to the class of systems that contains both rank-deficient and in-deficient input distribution matrices. The proposed scheme assumed the bounded external disturbance, therefore in future work, the adaptive law will be incorporated with sliding mode controller and results will be extended to a generalized class of affine nonlinear systems.

In this article, a new fault-tolerant control (FTC) method is presented for the Lipschitz nonlinear systems that is capable of handling the actuator faults, sensor faults, unknown external disturbances, and system uncertainties. An augmented system is first constructed by treating the sensor fault as an auxiliary state. An adaptive fault estimation scheme with an H∞ performance criterion is then developed to simultaneously estimate the actuator and sensor faults. To achieve the tracking control, a nonlinear sliding mode-based state feedback control law is proposed depending on the estimated states and information about fault from the fault estimating unit. The efficacy of the suggested technique is evaluated using a nonlinear model of the multirotor unmanned aerial vehicle (UAV) system with six degrees of freedom (DoF) motion. The proposed method is implemented in the inner loop subsystem in order to obtain the attitude and altitude tracking while the outer-loop control is simply a PID controller. Several simulations on the nonlinear system are performed to prove the effectiveness of the proposed method compared with the existing methods.

A composite control scheme based on a disturbance observer is presented in this paper to deal with the attitude control problem of flexible spacecraft. Specifically, a sliding mode disturbance observer (SMDO) is developed to attenuate the unmodeled system dynamics, parameter uncertainties, and multiple external disturbances. The key feature of this approach is to relax the assumption imposed on disturbance to be constant or changing at a slow rate, which is a typical assumption in this class of problems involving a disturbance observer. Then, an exclusive adaptive integral sliding mode controller is combined with the SMDO to get the improved closed-loop control performance of the system. The underlying benefit of the proposed control scheme is improved robustness against time-dependent external disturbances and system model uncertainties. The stability analysis of the closed-loop system is provided using Lyapunov’s stability theory. Simulation results are provided to show the effectiveness of the proposed control scheme, especially in comparison with existing results.

The attitude tracking control problem of flexible spacecraft subjected to parameter uncertainties, time-dependent external disturbances, actuator input nonlinearity, and input actuator misalignment is investigated in this paper. Explicitly, the proposed strategy addresses the input actuator misalignment and dead-zone issues that increase the controller design difficulties. Initially, a new second-order sliding mode observer (SoSMO) using an extended state approach is developed by adding a correction function to improve observer performance to estimate unwanted system perturbations. Then, a distinct SoSMO-based integral-type sliding mode control (ISMC) structure is designed in a unified manner to guarantee the asymptotic stability of the closed-loop system. Comparative numerical simulations under input actuator misalignment, the dead-zone nonlinearity, external disturbance, and inertia uncertainty are performed to illustrate the effectiveness of the proposed controller.