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This paper addresses the problem of heterogeneous multi‐agent systems (HMAS), comprising multiple uncrewed ground vehicles (UGVs) and multiple uncrewed aerial vehicles (UAVs), collaboratively monitoring the wildfire in the presence of actuator faults and communication link faults during the fire monitoring mission. It presents a fixed‐time fault‐tolerant dynamic formation control scheme designed for HMAS, with the objective of monitoring either the circular or elliptical propagation of a wildfire. The paper adopts a fixed‐time extended state observer (FxESO) to estimate the multi‐source disturbances arising from external disturbances and actuator faults, ensuring fixed‐time convergence of the estimation errors of the FxESO. By utilizing the Lyapunov candidate theorem, the collaborative tracking errors will converge to zero in fixed time, regardless of the initial position, ensuring that all agents in HMAS monitor the dynamic wildfire perimeter. Comparative simulation results are presented to illustrate the effectiveness of the proposed control scheme. The paper proposes a fixed‐time fault‐tolerant dynamic formation control scheme for heterogeneous multi‐agent systems (HMAS) consisting of both uncrewed ground vehicles (UGVs) and uncrewed aerial vehicles (UAVs) to collaboratively monitor wildfires in the presence of actuator faults and communication link faults. It utilizes a fixed‐time extended state observer (FxESO) to estimate disturbances and actuator faults, ensuring fixed‐time convergence of the estimation errors. The paper demonstrates the effectiveness of the proposed control scheme through comparative simulation results, showing that the collaborative tracking errors converge to zero in fixed time, enabling all agents in HMAS to monitor the dynamic wildfire perimeter regardless of their initial positions.

The marine environment is highly complex and variable, featuring obstacles such as islands, buoys, and vessels. Safe navigation of the surface agent (SA) fleet is crucial for ensuring the safety of the SA fleet, enhancing operational efficiency, and guaranteeing the smooth execution of the fleet’s mission. Regarding the problem of formation obstacle avoidance for SA fleets encountering complex obstacles during navigation, this chapter presents a fixed-time-based safe navigation algorithm for the SA fleet based on streamline traction. Firstly, to precisely position each SA at the designated location within the formation, a highly malleable leader–follower formation mode is introduced. Based on an enhanced interfered fluid dynamical system (EIFDS) obstacle avoidance algorithm, the virtual Leader is guided to evade static obstacles and determine a trajectory of the designated position. Secondly, a first-order fixed-time control Lyapunov function (FTCLF) is designed based on the EIFDS obstacle avoidance algorithm to guide the angular velocity constraint. The optimal guiding angular velocity signal is obtained through quadratic programming, ensuring that the SA steers towards the designated position while avoiding obstacles. Next, for the guiding velocity amplitude signal, a first-order fixed-time control barrier function (FTCBF) is designed based on the streamline formation scheme and the inter-boat safety distance to guide the velocity amplitude constraint. The optimal guiding velocity amplitude signal is obtained through quadratic programming, guaranteeing that each SA maintains the formation while avoiding collisions with adjacent vessels. Finally, the simulation results indicate the effectiveness, superiority, and stability of the proposed fixed-time-based safe navigation guidance algorithm for the SA fleet based on streamline traction.

In this paper, we emphasize on a novel fast fixed-time control strategy and its application to fixed-time synchronization control of semi-Markov jump delayed Cohen-Grossberg neural networks (SMJDCGNNs). First, we consider a class of SMJDCGNNs. Second, a novel fast fixed-time control strategy is proposed and designed to control the considered delayed system to achieve global synchronization within the derived fixed settling time. Third, the advantages of the derived theoretical results are discussed. Finally, we give a numerical example to show the effectiveness and feasibility of the obtained theoretical results.

This article investigates the fixed-time trajectory tracking control of a free-flying rigid space manipulator perturbed by model uncertainties and external disturbances. A novel robust fixed-time integrated controller is developed by integrating a nominal fixed-time proportional–differential-like controller with a fixed-time disturbance observer. It is strictly proved that the proposed controller can ensure the position and velocity tracking errors regulate to zero in fixed time even subject to lumped disturbance. Benefiting from the feedforward compensation, the proposed controller has the strong robustness and excellent disturbance attenuation capability. The effectiveness and advantages of the proposed control approach are validated through simulations and comparisons.

This paper investigates the problem of fixed-time tracking control for a class of high-order nonlinear systems with matched disturbances. A novel continuous fixed-time sliding mode disturbance observer is first proposed to accurately estimate the external disturbances. Then, a new integral high-order sliding mode (IHOSM) surface is proposed in the sense of fixed-time stability by the bi-limit homogeneous method. Subsequently, utilizing the disturbance estimation information, an IHOSM-based fixed-time control scheme is proposed which can enforce the closed-loop control system reach the real sliding mode surface. Meanwhile, it is applied to an error dynamic system of a wheeled mobile robot to achieve fast accurate trajectory tracking. Finally, the comparative experiment results demonstrate the effectiveness and superiority of the proposed control approach.

This paper introduces a homogeneous controller along a fixed-time state and fault observer for finite-time stabilization and fault accommodation of a remotely-operated vehicle in the presence of actuator saturation and rate limits. For this, a novel tuning algorithm is improvised for manipulating the degree of homogeneity in homogeneous controllers to effectively acquire different properties from the overall control system. The tuning of degree of homogeneity is based on vehicle’s velocity. The proposed algorithm results in a switching-type controller, which undergoes three different stages during the operation, to eliminate the sensitivity of conventional finite-time and fixed-time controllers to large initial errors in the presence of thruster constraints. In addition, a new fixed-time fault and state observer is designed for the realization of output feedback control and fault tolerance by combining a fixed-time state observer with a fault estimation unit. In contrast to conventional extended-state observers, this observer considers the dynamics of the thruster system in its formulation so that better performance can be provided for the control system upon thruster failures. Control allocation is utilized to accommodate thruster failures and faults and to take account of thruster saturation and rate limits. Stability analyses are carried out for the overall control system and the proposed observer. It is shown that the closed-loop control system would be globally finite-time stable. The state estimation subsystem is fixed-time stable and the fault estimation unit is input-to-state stable. Simulations are carried out and comparisons are made with several finite-time and fixed-time controllers to outline the advantages of the proposed homogeneous controller and the benefits of the overall fault-tolerant control system.

This paper presents fractional order fixed-time nonsingular terminal sliding mode control for stabilization and synchronization of fractional order chaotic systems with uncertainties and disturbances. First, a novel fractional order terminal sliding mode surface is proposed to guarantee the fixed-time convergence of system states along the sliding surface. Second, a nonsingular terminal sliding mode controller is designed to force the system states to reach the sliding surface within fixed-time and remain on it forever. Furthermore, the fractional Lyapunov stability theory is used to prove the fixed-time stability and the robustness of the proposed control scheme and estimate the upper bound of convergence time. Next, the proposed control scheme is applied to the synchronization of two nonidentical fractional order Liu chaotic systems and chaos suppression of fractional order power system. Simulation results verify the effectiveness of the proposed control scheme. Finally, some application issues about the proposed scheme are discussed.

The adaptive fixed-time control problem for nonlinear systems with time-varying actuator faults is investigated in this paper. A novel adaptive fixed-time controller is designed via combining the Lyapunov stability theory with the backstepping method. It can be adapted to both system uncertainties and unknown actuator faults. Compared with the existing fault-tolerant control schemes subject to actuator faults, the adaptive fixed-time neural networks control scheme can make sure that the tracking error is convergent in a small neighborhood of the origin within a fixed-time interval, and it does not depend on the original states of the system and actuator faults. In light of the control scheme proposed in this paper, the fixed-time stability of the closed-loop system can be guaranteed by theoretical analysis, and a numerical example is provided to verify the effectiveness of obtained theoretical results.

The attitude-tracking problem of hypersonic morphing vehicles (HMVs) is investigated in this research. After introducing variable-span wings, the optimal aerodynamic shape is available throughout the entire flight mission. However, the morphing wings cause significant changes in aerodynamic coefficients and mass distribution, challenging the attitude control. Therefore, a complete design procedure for the flight control system is proposed to address the issue. Firstly, the original model and the control-oriented model of HMVs are built. Secondly, in order to eliminate the influence caused by the multisource uncertainties, an adaptive fixed-time disturbance observer combined with fuzzy control theory is established. Thirdly, the fixed-time control method is developed to stabilise hypersonic morphing vehicles based on a multivariable sliding mode manifold. The control input can be obtained directly. Finally, the effectiveness of the proposed method is proved with the help of the Lyapunov theory and simulation results.

The article explores the fixed-time tracking control (FTTC) problem of strict-feedback nonlinear systems with unmodeled dynamics and dynamic disturbances. For the first time, a novel fixed-time dynamic signal is presented to address unmodeled dynamics. Associating adaptive backstepping control technology and fixed-time Lyapunov stability theory, an adaptive FTTC strategy is constructed, which guarantees that all signals of the closed-loop system are bounded and the tracking error can converge to a small region of zero within a fixed-time range. Finally, two simulation results illustrate the feasibility and validity of the suggested strategy.