Time-varying External Disturbances Research Articles

Distributed Cooperative Fault-Tolerant Control of High-Speed Trains With Input Saturation and Actuator Faults

In this work, a novel distributed fault-tolerant control strategy is proposed for cooperative operation of high-speed trains (HSTs) subject to unmodeled dynamics, time-varying external disturbances, input saturation and actuator partial failures. The cooperative control of HSTs is first transformed to the consensus problem of a multi-agent system. Then, the distributed control laws that are equipped with a command filter and an adaptive neural network are developed to achieve the consensus task among the HSTs with predefined displacement and speed profiles. Further, an auxiliary dynamical system is introduced to compensate for the influence of input saturation. Moreover, an adaptive failure compensation strategy is designed to deal with the unknown and time-varying actuator faults. The convergence of the proposed controller is analyzed rigorously by applying the Lyapunov theorem, and the effectiveness is demonstrated by numerical simulations.

Sliding-Mode Synchronization Control of Complex-Valued Inertial Neural Networks With Leakage Delay and Time-Varying Delays

This work explores the synchronization problem of two nonidentical complex-valued inertial neural networks (CVINNs) considering time-varying delays, leakage delay, and external disturbances. The entire analysis does not use reduced-order conversion, nor does it involve the separation of real and imaginary parts, but directly focuses on the original system. First, an integral sliding-mode surface suitable for the system is proposed. Second, the efficient sliding-mode control laws are designed, under which the state trajectories of the closed-loop dynamic error systems can be driven onto the predefined sliding-mode surface in finite time. Then, not requiring the time-varying delays to be differentiable, by constructing innovative Lyapunov–Krasovskii functionals, the synchronization criteria are obtained in the forms of the linear matrix inequality techniques. Eventually, for the systems with different types of activation functions, the corresponding numerical verification and comparison are carried out.

Intelligent VIV control of 2DOF sprung cylinder in laminar shear-thinning and shear-thickening cross-flow based on self-tuning fuzzy PID algorithm

A self-tuning fuzzy PID (ST-FPID) control scheme is implemented within a joint interactive (Matlab/Simulink/Fluent) co-simulation framework for effective two degrees of freedom (2DOF) vortex-induced vibration (VIV) control of an elastically-mounted circular cylinder in laminar cross-flow of incompressible non-Newtonian power-law fluids based on the control action of a single transverse force actuator. The model-free controller, which systematically tunes the control parameters online in real time based on given rules, is well-known to be highly advantageous over the previously employed conventional PID controllers. It is particularly capable of handling the intricate non-linear dynamic effects inherent in the complex fluid rheology of non-Newtonian flow past the cylinder in presence of unmodeled system dynamics, high parametric uncertainties, diverse operational conditions, and time-varying external disturbances and control signals. Extensive numerical simulations reveal that the complex shear-thinning and shear-thickening behaviors of fluid viscosity can substantially influence the cylinder dynamic response, applied hydrodynamic forces, and flow structure. In particular, effectiveness and high performance of the adopted ST-FPID control strategy in substantial suppression of the high amplitude coupled 2DOF VIV of the elastically-mounted cylinder at selected critical reduced velocities in the lock-in region are established for a wide range of power-law index parameters (e.g., up to 83% reduction in RMS value of cylinder cross-flow displacement and up to 35% reduction in RMS value of cylinder in-line displacement for n=1and U* = 5 at Re = 100). Also, the vigorous action of the error-driven ST-FPID controller in forcing the high strength vortex shedding patterns of the uncontrolled cylinder out of the lock-in condition into the classical von Kármán vortex street of 2S-type mode of moderately weaker strengths is verified.

Reduced-order filtering for semi-Markovian jump systems against randomly occurring false data injection attacks

This paper describes a mode-dependent reduced-order filtering problem for semi-Markovian jump systems with time-varying delay and external disturbance, where the measurement output is vulnerable to randomly occurring false data injection attacks. To facilitate analysis, the attacks are described by a nonlinear function that meets Lipschitz continuity and the possible attack scenarios are represented by a stochastic parameter that follows the Bernoulli distribution. Based on the information from the considered system and reduced-order filter, an augmented filtering system is constructed. Then, a convex optimization problem is formulated by using Lyapunov-Krasovskii stability theory and stochastic analysis. The filter gain matrices are efficiently derived as a result, ensuring that the augmented filtering system is stochastically stable and strictly (Q,S,R)−γ-dissipative. Through numerical examples, the advantages and effectiveness of the developed theoretical findings are clearly demonstrated.

Robust Saturated Formation Tracking Control of Multiple Quadrotors With Switching Communication Topologies

This article deals with distributed formation control for a set of quadrotors subject simultaneously to external disturbances and switching communication topologies. The proposed robust controller incorporates position and attitude control laws for each quadrotor. Both control laws have a nominal part for trajectory tracking and a robust part that compensates for the dynamic model uncertainties and time-varying external disturbances. The devised controller guarantees that the thrust force is bounded with respect to the position error by utilizing saturation functions. The directed communication topology among the quadrotors is considered to be switchable. The formation control performance is guaranteed under switching topologies, and it is demonstrated that all error terms, in closed-loop, converge to a ball centered at the origin with an arbitrarily small radius, achieving uniformly ultimate boundedness. Finally, the performance of the proposed strategy is validated through numerous simulation and experimental examples.

Autonomous Underwater Vehicle Positioning Control - a Velocity Form LPV-MPC Approach*

In this work, the positioning control of an autonomous underwater vehicle (AUV) is considered for docking operations in the presence of varying tidal currents. The AUV model is described by a dynamic model and a kinetic model, both are linear parameter varying (LPV). A velocity form LPV model predictive control (LPV-MPC) scheme is proposed, in which the AUV dynamic model is used for the states and the kinetic model is used for the output. The interdependence of AUV kinematic model and dynamic model is exploited to avoid increased state dimension. The complete velocity form controller design enables the cancellation of disturbance effects through the use of the AUV's velocity vector increment for predicting the future evolution of the system. Compared to the original predictive control for the Naminow-D AUV that uses a time-varying Kalman filter for state estimation to approximate disturbances, the proposed algorithm does not require an estimator to eliminate unknown current disturbance, therefore simplifies design and implementation. Simulation studies show the merit of the proposed controller over the original Naminow-D predictive controller especially in terms of improved transient response and reduced sensitivity to time-varying external disturbances.

Membership function dependent stabilization of discrete time interval type-2 fuzzy systems with mixed actuator faults

This paper investigates the problem of mixed actuator failures for discrete-time interval type-2 (IT-2) fuzzy systems with time-varying delays and external disturbances. Applying the non-parallel compensation strategy, the IT-2 fuzzy controller is designed. Considering the nonlinear fault factors of actuator, the linear fault model is expanded, which is more general than the conventional mixed actuator failure model. The information of membership function is introduced by staircase function approximation. Based on Lyapunov stability theory and a series of matrix inequality scaling techniques, a membership function dependent stability criterion with H∞ performance is obtained. Then, the effectiveness of the proposed conclusion is verified by two simulation examples.

State-dependent finite-time controller design and its application to positioning control task for underactuated unmanned surface vehicles

In this study, an accurate state-depended finite-time positioning control framework is proposed for underactuated unmanned surface vehicles (USVs). Three control objectives have been developed to guide the surge, sway, and yaw motions, where the surge and yaw motions are directly controlled by the USV propulsion system. Due to the USV’s underactuated actuator configuration, the sway motion is indirectly affected by the input of sway disturbance force whose magnitude and direction have sustained variations via the adaption of vehicle heading. To handle the problems associated with heading assignment, time-varying external disturbances, as well as modeling and parameter uncertainties, a state-dependent finite-time controller has been proposed to realize these control objectives. The proposed controller is composed of two parts, namely an online state-constrained polynomial planning and an uncertainty-estimated control execution. The function of this state-constrained polynomial planning is to satisfy all the system state constraints and generate the planning acceleration for the control law execution. Relying on an accurate estimation of unknown uncertainties, the control law is executed at high frequency and established as an algebraic formulation. The system convergence controlled by the proposed scheme is then analyzed. Simulated studies and experimental validations were carried out to verify the proposed controller for the positioning control task from the perspective of effectiveness and robustness.

Distributed time-varying formation optimal tracking for uncertain Euler–Lagrange systems with time-varying cost functions

This article studies the distributed formation optimal tracking problems for Euler–Lagrange systems, where each agent only has access to local cost function and other relative state information with its neighbors. Different from existing works, the effects of time-varying formation, parametric uncertainties, external disturbances and optimal performance of Euler–Lagrange systems are all considered simultaneously. Under the proposed distributed formation optimal tracking protocol, all agents are able to asymptotically track an optimal reference trajectory, while maintain the given time-varying formation. Firstly, a dynamic system is introduced for each agent to generate optimal reference signal, which uses only the individual's own state and the neighboring relative measurements with no extra exchange of virtual states needed. Then, an optimal tracking control strategy is proposed, with which zero optimum-tracking error can be achieved. Thirdly, sufficient conditions are given to guarantee that the agents' states asymptotically converge to the optimal solution in the desired formation under the proposed algorithm. At last, numerical simulation is designed to verify the strategies.

Distributed finite-time velocity-free robust formation control of multiple underactuated AUVs under switching directed topologies

This paper proposes a distributed finite-time velocity-free robust formation control scheme for multiple underactuated autonomous underwater vehicles (AUVs) under switching directed topologies in the presence of uncertain dynamics and unknown time-varying external disturbances. Here, a novel finite-time velocity observer is created for each AUV to estimate its neighbors’ velocities within a finite time so that only its neighbors’ positions need to be transmitted, which reduces the communication burden between AUVs. Then, a super-twisting extended state observer is constructed for each AUV to estimate its total disturbances lumped by the uncertain dynamics and the unknown time-varying external disturbances, whose estimation errors can converge to zero within a finite time. Further, a distributed finite-time velocity-free robust formation control law is proposed incorporating the above into the nonsingular terminal sliding mode technique. Theoretical analysis and simulation results indicate that the proposed formation control law can make the multiple AUVs achieve the desired formation pattern while guaranteeing the formation errors converge to zero within a finite time.

Composite disturbance observer-based backstepping stabilisation for 3-DOF ship-borne platform with unknown disturbances

ABSTRACT A composite anti-disturbance stabilisation control scheme is presented for the ship-borne platform system with completely unknown disturbances. The completely unknown disturbances consist of external time-varying disturbances and norm-bounded unmodelled dynamics. The composite anti-disturbance control scheme is built through integrating the nonlinear disturbance observer and the robustifying term with the vectorial backstepping technique. The nonlinear disturbance observer is designed to provide the on-line estimations of external time-varying disturbances such that the disturbance compensation term is introduced into the control design. The robustifying term with the adaptive law is employed to attenuate norm-bounded unmodelled dynamics. On the basis of the vectorial backstepping technique, the composite anti-disturbance control law is derived. The composite anti-disturbance control structure consists of the outer layer with the nonlinear disturbance observer for external time-varying disturbance cancellation as well as the inner layer with the vectorial backstepping control together with the robustifying term for unmodelled dynamic attenuation. By means of the Lyapunov stability theory, it is proven that the composite anti-disturbance stabilisation controller can achieve the disturbance rejection and attenuation simultaneously. It is verified by illustrative simulations that the composite anti-disturbance stabilisation control scheme can effectively stabilise the ship-borne stabilisation platform.

Design and full-link trajectory tracking control of underwater snake robot with vector thrusters under strong time-varying disturbances

In this paper, an underwater snake robot with vector thrusters and axis-intersect joints is designed. The dynamic model of the newly designed robot is established. A new decoupling control strategy is proposed for full-link trajectory tracking. The control strategy decouples the movements between the body and the links. The trajectory of the body (represented by the head link) is controlled by thrusters, and the rest links follow its trajectory by controlling the relative angles to the head link with servo motors on the joints. To eliminate the influence of strong time-varying external and internal disturbances, the control method based on sliding mode and a nonlinear disturbance observer with linear matrix inequality is proposed to realize the full-body trajectory tracking. The results show that the proposed method performs better than the reference under strong time-varying external and internal disturbances.

NLS Based Hierarchical Anti-Disturbance Controller for Vehicle Platoons With Time-Varying Parameter Uncertainties

Cooperative adaptive cruise control (CACC) is a promising technology for vehicle platoons to increase roadway capacity. This paper proposes a networked Lagrange system (NLS) based CACC dynamic model based on which a hierarchical anti-disturbance controller is developed to solve the stability problem of CACC in vehicle platoons with time-varying parameter uncertainties, external disturbances, and directional dynamic communication topology. First, a hierarchical anti-disturbance controller for NLS is constructed which comprises three layers, these are, the adaptive smooth estimator-control layer, the distributed classifying amplitude-related layer, and the anti-disturbance control layer, in which the parameter uncertainties are estimated in the adaptive smooth estimator-control layer, the disturbance classification and distribute control are executed in the distributed classifying amplitude-related layer and the anti-disturbance control layer respectively. In addition, the proposed controller is extended to address the stability problem of CACC in vehicle platoons with time-varying parameter uncertainties, external disturbances, and directional dynamic communication topology conditions, which shows the versatility of the controller. Finally, comparison studies and simulation results are provided to demonstrate the effectiveness, significance, and advantages of the presented controllers.

Sliding-Mode-Based Admissible Consensus Tracking of Nonlinear Singular Multiagent Systems Under Jointly Connected Topologies.

The admissible consensus tracking problem of nonlinear singular multiagent systems (SMASs) with time-varying delay, uncertainties, and external disturbances under jointly connected topologies is investigated in this article. First, the sliding-mode control (SMC) is applied to effectively reduce the adverse effects of uncertainties and nonlinearities of systems. Then, by the combination of admissible analysis, the Cauchy convergence criterion, and SMC, the sufficient conditions for the admissible consensus tracking and disturbance rejection of SMASs under jointly connected topologies are provided. Furthermore, a distributed SMC law is designed such that the sliding-mode dynamics trajectories reach the sliding surface in finite time. Finally, the simulation results are utilized to indicate the effectiveness of the presented methods.

Finite-Time Neuro-Sliding-Mode Controller Design for Quadrotor UAVs Carrying Suspended Payload

Due to the quadrotor’s underactuated nature, suspended payload dynamics, parametric uncertainties, and external disturbances, designing a controller for tracking the desired trajectories for a quadrotor that carries a suspended payload is a challenging task. Furthermore, one of the most significant disadvantages of designing a controller for nonlinear systems is the infinite-time convergence to the desired trajectory. In this paper, a finite-time neuro-sliding mode controller (FTNSMC) for a quadrotor with a suspended payload that is subject to parametric uncertainties and external disturbances is designed. By constructing a finite-time sliding mode controller, the quadrotor can follow the reference trajectories in finite time. Furthermore, despite time-varying nonlinear dynamics, parametric uncertainties, and external disturbances, a neural network structure is added to the controller to effectively reduce chattering phenomena caused by high switching gains, and significantly reduce the size of the control signals. Following the completion of the controller design, the system’s stability is demonstrated using the Lyapunov stability criterion. Extensive numerical simulations with various scenarios are run to demonstrate the effectiveness of the proposed controller.

Online recorded data-based finite-time composite neural trajectory tracking control for underactuated MSVs.

This paper presents an online recorded data-based composite neural finite-time control scheme for underactuated marine surface vessels (MSVs) subject to uncertain dynamics and time-varying external disturbances. The underactuation problem of the MSVs was solved by introducing the line-of-sight (LOS) method. The uncertain dynamics of MSVs are approximated by the composite neural networks (NNs). A modified prediction error signal is designed by virtue of online recorded data. The weight updating law of NN is driven by both tracking error and prediction error, introducing additional correction information to the weights of NN, thus improving the learning ability of the NN. Furthermore, disturbance observers can be devised to estimate the compound disturbances consisting of the approximation errors of NNs and external disturbances. Moreover, the smooth function is inserted into the design of the control scheme, and the finite-time composite neural trajectory tracking control of MSVs is achieved. The stability of the MSVs trajectory tracking closed-loop control system is guaranteed rigorously by the Lyapunov approach, and the tracking error will converge to the set of residuals around zero within a finite time. The simulation tests on an MSV verify the effectiveness of the proposed control scheme.

Trajectory tracking control for autonomous underwater vehicle with disturbances and input saturation based on contraction theory

Autonomous underwater vehicle (AUV) is a complex nonlinear system and its control is accompanied by various challenges. This paper focuses on the three dimensional (3D) trajectory tracking control of a fully-actuated AUV in the presence of model uncertainties, unmeasured velocity, time-varying external disturbance and input saturation. First, taking the model uncertainties and external disturbances as the total disturbances, an extended state observer (ESO) is designed to estimate the unmeasured velocity and total disturbances. Then, the saturated controller based on contraction theory and its application in singular perturbation system (SPS) is obtained so that the AUV tracks the desired trajectory and avoids exceeding the limit of the actuator. The estimation error, tracking error and the error between the ideal controller and the actual controller are analyzed by contraction theory, and the explicit bounds of these errors are given. At last, comparative numerical simulations are provided to show the effectiveness of the ESO and the advantages of the saturated controller.

Boundary control of multiple-sectioned flexible marine riser with time-varying output constraint

This article addresses the problem for vibration suppression of a multiple-sectioned marine riser system subject to time-varying external disturbances and asymmetric output constraint. Under the assumption that continuity constraint, multiple-sectioned marine riser’s dynamics are described by some continuously connected partial differential equations (PDEs) coupled with an ordinary differential equation (ODE). We only employ boundary control mechanism that suppresses system’s vibration displacements and compensate the influence of external disturbances. A novel and improved disturbance observer is proposed to estimate unknown boundary disturbance and two different barrier Lyapunov functions are constructed to prevent the time-varying constraint violation. Based on the backstepping technology and Lyapunov-based control, a boundary controller is presented to accomplish the control objectives. Moreover, the uniform boundedness and stability of the closed-loop system are rigorously guaranteed. Finally, simulation results are provided to illustrate the effectiveness of the designed control scheme.

Fast fixed-time vertical plane motion control of autonomous underwater gliders in shallow water

In this paper, a fast fixed-time vertical plane motion controller is proposed for autonomous underwater gliders (AUGs) gliding in shallow water. The influence of speed-sensorless conditions, model uncertainties, unknown time-varying external disturbances, input saturations, and state delay are taken into account. To improve control performance, a fast fixed-time stable system is first presented. Based on the system, an adaptive extended state observer (ESO) is developed for estimating speed, model uncertainties, and external disturbances. A fast fixed-time controller is designed for improving the gliding efficiency and reducing the risk of hitting the ocean floor. Moreover, an input saturation auxiliary system and an advance compensation method are presented to cope with input saturations and state delay. According to Lyapunov theory, it is proved that the AUG states can converge into a small neighborhood within a fixed time. Finally, simulation results demonstrate the rapidity and effectiveness of the designed control method.

Adaptive robust finite-time tracking control for quadrotor subject to disturbances

Quadrotors are extremely agile UAVs with many unknowns regarding their moment of inertia, drag coefficients, and mass. Aside from aerodynamic turbulence, the quadrotor has a high level of nonlinearity due to its underactuated mechanical system. These last two factors cause issues that necessitate adaptive and robust control. A hybrid robust nonlinear control approach for a quadrotor is described in this research paper. To address the quadrotor trajectory tracking problem, a combination of backstepping and sliding-mode approaches based on proportional integral derivative (PID) surfaces is developed, with the Lyapunov method used to evaluate the control system’s stability. The adaptive technique, in conjunction with sliding-mode and super-twisting algorithm, is then investigated in order to reduce the chattering impact of sliding mode control and estimate the various controller parameters. Super-twisting adaptive backstepping PID sliding mode approach for the quadrotor rotational and translational subsystems is presented to reduce error convergence time and improve speed tracking performance. The simulation results under various scenarios (parameters uncertainties under Gaussian random disturbances, constant and time-varying external disturbance) are given to demonstrate the efficacy and practicability of the proposed control. A comparative analysis is performed with different developed controllers using the performance of the integral of absolute error and the integral of the absolute value of the derivative of the control inputs to demonstrate the superiority and effectiveness of the designed control technique.