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This paper investigates the finite-time time-varying formation-containment control problem for satellite formation flying under discontinuous control protocols based on nonsmooth analysis. The desired consequence is that the follower satellites can converge into a dynamic convex hull in finite time, which is spanned by leader satellites' time-varying formation according to the reference signal. Firstly, to accomplish this objective, a finite-time time-varying formation-containment control strategy is proposed for satellite formation system in present of the bounded disturbances and satellites' accelerations, which are known for each satellite. Then, considering the case that the information of disturbances may not be measured accurately and the accelerations of satellites may not be obtained globally in some practice application scenarios, a fully distributed adaptive control strategy is proposed by introducing the dynamic variables. The adaptive variables can compensate the unknown items and adjust with the evolution of neighbour satellites' states, which makes the controller more flexible. Moreover, the proposed control strategies are able to guarantee a fast dynamic response and also a suppression of disturbance. Finally, the performances of the proposed strategies are demonstrated by numerical simulations. [ABSTRACT FROM AUTHOR]

This paper presents the predefined-time convergent robust controller design for a brushed direct current (DC) motor system affected by matched and unmatched deterministic disturbances and stochastic noises, considering both fully measurable and incompletely measurable states. The control algorithm allows the control designer to set the convergence time a priori. The convergence time is independent of initial conditions and disturbances and noises affecting the system. Numerical simulations are conducted to demonstrate efficiency of the designed control algorithm. The obtained results show that the control algorithm counteracts the matched and unmatched disturbances, and noises in case of fully measurable states and mitigates their influence in case of incompletely measurable ones. [ABSTRACT FROM AUTHOR]

This paper addresses a problem of optimal error quantification in the framework of robust control theory in the 1 setup. The upper bounds of biased external disturbance and the gains of coprime factor perturbations in a discrete-time linear time invariant SISO plant are assumed to be unknown. The computation of optimal data-consistent upper bounds under a known bias of external disturbance has been simplified to linear programming. This allows for the computation of optimal estimates in real-time and their application to achieve optimal robust steady-state tracking even when facing an unknown bias in the external disturbance. The presented results have been illustrated through computer simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a modification of a Sliding Mode Classical Observer (SMCO) to adapt it to the fractional approach. This adaptation involves using a set of definitions based on fractional calculus theory, particularly the approach developed by Riemann–Liouville, resulting in a Sliding Mode Fractional Observer (SMFO). Both observers are used to perform disturbance reconstruction considered additive in a Quadrotor Unmanned Aerial Vehicle (UAV) model. Then, this work presents the fractional-order sliding mode observer's mathematical formulation and integration into the Quadrotor UAV model. To validate the quality of the disturbance reconstruction process of the proposed SMFO observer scheme, numerical simulations are carried out, where a reconstruction quality indicator (BQR) is proposed based on the analysis of performance indices such as the Mean Square Error (MSE), the First Probability Moment (FPM), and Second Probability Moment (SPM), which were obtained for both the SMCO and the SMFO. The simulation results demonstrate the efficacy of the proposed observer in accurately reconstructing disturbances under various environmental conditions. Comparative analyses with SMCO highlight the advantages of the fractional-order approach in terms of reconstruction accuracy and improvement of its transitory performance. Finally, the presented SMFO offers a promising avenue for enhancing the reliability and precision of disturbance estimation, ultimately contributing to the advancement of robust control strategies for Quadrotor UAV systems. [ABSTRACT FROM AUTHOR]

This paper presents a novel robust control algorithm to improve the trajectory tracking accuracy for a class of serial manipulators with unknown uncertainties. Firstly, the manipulators' dynamics is established based on the Lagrangian method, and the intrinsic properties in the dynamical model of uncertain serial manipulators are investigated, resulting in a better match between the dynamical model and the physical systems. Then, based on the upper bound of the uncertainties, a nonlinear robust controller is designed. Here, a higher-order term is invoked in the controller design to further suppress the influence of the uncertainties. As supported by rigorous proofs, the uniform boundness and uniform ultimate boundness of the controlled manipulator under the designed controller are obtained with the Lyapunov–Minimax method. Finally, a numerical simulation and an experiment of the designed controller are implemented on a two-degree-of-freedom manipulator. [ABSTRACT FROM AUTHOR]

Due to the breadth and complexity of spatial motion, and the nonlinear coupling caused by multiple degree-of-freedom, the control difficulties of spatial cooperative multirobot system are two mainly aspects, the modeling method and the dispose of uncertainty. For modeling, the process of directly using ordinary methods such as Lagrange mechanics are very complex. For control, the external disturbances and imperceptible errors will lead to the instability of dynamic system, these factors are collectively referred to as uncertainty. In this paper, a universal modeling method based on spatial cooperative multirobot system was proposed, and an adaptive robust controller was designed to solve the control problems. Simplify the connection link into a load and divide the system into two symmetrical subsystems by disconnecting the load center. The inherent physical position and given trajectories were unified as constraints. The constraints applied on system are creatively converted into consistent standard form through the Udwadia-Kalaba (U-K) method, and the corresponding constraints can be generated easily from the Udwadia-Kalaba basic equations. In addition, a nominal term to stable the system and an adaptive term was added to the controller. The adaptive term works through an adaptive parameter, the parameter estimates the uncertainty bound, thus, only the boundedness of uncertainty should be known, and more accurate control input can be gained. Eventually, the correctness of the model and controller has been confirmed through numerical simulation. [ABSTRACT FROM AUTHOR]

A decentralized robust control algorithm for robotic manipulator in joint space is proposed, in which the linkage and its joint driver are treated as a module with a torque sensor installed on its driver shaft connecting the successive module. Due to the coupling between two connected dynamic modules can be measured by the torque sensor, the computation of the nonlinear coupling effect caused by the rest upper linkages is no longer needed, which means the complexity of the dynamic equations of the manipulator will be greatly reduced and the real-time compensation calculation of manipulator dynamics is not required in its control loop. Furthermore, the joint torque sensor enables the feedback of the external disturbance and gravity load acting on the linkage, which equips the control system with a strong anti-interference capability. Since there is no need to compute the feedforward compensation joint torque, the structure of the control system becomes simple and the joint controller can be independently designed. An integral adaptive compensator is specifically designed to deal with the compensation of the dynamic coupling from the low linkages because such coupling cannot be sensed by the joint torque sensor. A robust control strategy was proposed to compensate for the friction parameter variation between the modules of the manipulator and the uncertainty caused by the reconfiguration of the manipulator. The computer simulation is conducted to verify the effectiveness of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

This paper investigates the terminal sliding-mode control (TSMC) with predefined-time stability (PTS) for a disturbed quadrotor system (DQS). First, for both the rotational and translational subsystems of the DQS, a novel notion of predefined-time terminal sliding-mode manifold (PTTSMM) is created. Using the proposed PTTSMM method, the DQS state variables reach their origin in a predefined-time. The influence of disturbances is taken into consideration in the design of the suggested control to show its performance. A formal analysis technique is also provided, as well as the stability of the closed-loop DQS. The performance and effectiveness of the predefined-time method proposed in this work are illustrated by numerical simulations and also comparison study with other control techniques is presented. [ABSTRACT FROM AUTHOR]

This article presents the development of a new combined controller based on an active steering system and an active braking system to increase maneuverability and the directional stability of the vehicle. First, to dominate the uncertainties of the dynamic model, sliding model control (SMC) method has been used. Then, to verify the performance of the proposed controller, a control system has been designed based on linear quadratic regulator (LQR) control method. Next, to investigate the performance of the controllers, a 14 degree-of-freedom (DOF) dynamic model has been utilized. The computer simulations confirmed the effectiveness of the robust controller in comparison with the LQR control system during critical maneuver. [ABSTRACT FROM AUTHOR]

In this paper, the constrained control of systems evolving on matrix Lie groups with uncertainties is considered. The proposed methodology is composed of a nominal Model Predictive Control (MPC), and a feedback controller. The previous work on the control of systems on manifolds is applied to design the nominal MPC, which generates the nominal trajectory. In the nominal MPC, the state and input constraints on the Lie group are transformed into the constraints on the Euclidean space. While to deal with uncertainties, the feedback control used to track the nominal trajectory is designed directly on the Lie group. The tracking error in the feedback control is proved to be bounded in invariant sets, which are further used to revise the constraints in nominal MPC. We prove that the input‐to‐state stability of the entire system under the proposed control methodology with respect to the disturbances can be achieved. The proposed methodology is applied to the constrained attitude control of rigid bodies with uncertainties. In the application example, the detailed mathematical proof and the comparative numerical simulation are presented to demonstrate the feasibility of the proposed methodology. [ABSTRACT FROM AUTHOR]

This paper proposes a robust control allocation for the capture control of the space inertial sensor's test mass under overcritical conditions. Uncertainty factors of the test mass control system under the overcritical condition are analyzed first, and a 6-DOF test mass dynamics model with system uncertainty is established. Subsequently, a time-varying weight function is designed to coordinate the allocation of 6-DOF generalized forces. Moreover, a robust control allocation method is proposed to distribute the commanded forces and torques into individual electrodes in an optimal manner, which takes into account the system uncertainties. This method transforms the robust control allocation problem into a second-order cone optimization problem, and its dual problem is introduced to simplify the computational complexity and improve the solving efficiency. Numerical simulation results are presented to illustrate and highlight the fine performance benefits obtained using the proposed robust control allocation method, which improves capture efficiency, increases the security margin and reduces allocation errors. [ABSTRACT FROM AUTHOR]

In this paper, a protocol for nondestructive parity meter (NPM) of two cat‐state qubits is proposed. The physical model contains two cavities and an auxiliary qubit. For each cavity, the quantum information is encoded on the odd and even cat state, forming a cat‐state qubit. By adjusting the strength of the driving field on the auxiliary qubit, an effective Hamiltonian for cavity‐selective transition is derived. Moreover, reverse engineering based on the effective Hamiltonian is applied to find the evolution path, and the systematic‐error‐sensitivity nullification method is used to select proper parameters of the evolution path. In this way, robust control fields are designed to combat the influence of the systematic errors. Furthermore, the effects of random noise and decoherence on the fidelity of the protocol are considered. Numerical simulations show that the protocol is insensitive to the experimental imperfection, including systematic errors, random noise and decoherence. Therefore, the protocol is expected to expand the vision of realizing NPM. [ABSTRACT FROM AUTHOR]

The main goal of estimating models for industrial applications is to guarantee the cheapest system identification. The requirements for the identification experiment should not be allowed to affect product quality under normal operating conditions. This paper deals with ensuring the required liquid levels of the cascade system tanks using the model predictive control (MPC) method. The MPC strategy was extended with the Kalman filter (KF) to predict the system’s succeeding states subject to a reference trajectory in the presence of both process and measurement noise covariances. The main contribution is to use the application-oriented input design to update the parameters of the model during system degradation. This framework delivers the least-costly identification experiment and guarantees high performance of the system with the updated model. The methods presented are evaluated both in the experiments on a real process and in the computer simulations. The results of the robust MPC application for cascade system water levels control are discussed. [ABSTRACT FROM AUTHOR]

In this paper, a self-tuning Robust Integral of Sign of Error (RISE)-based backstepping controller is designed for an electro-hydraulic arm system with a fourth-order system model. The RISE controller, which constitutes the robust part of the control rule, is fused with a backstepping control strategy to cope with model-based and parametric uncertainties. Different from a classical RISE control rule, a tanh ⁡ (⋅) function is used instead of a sgn (⋅) function to obtain a more smooth control signal. All the gains in the RISE controller are tuned by using continuous update rules. The efficiency of the controller is demonstrated by conducting numerical simulations. [ABSTRACT FROM AUTHOR]

This paper mainly focuses on the cooperative robust consensus tracking problem of uncertain networked Euler-Lagrange systems (NELSs) with time-varying delays and output constraints. By systematically integrating the neural network (NN) adaptive technique and the logarithmic type Barrier Lyapunov Function (BLF) in combination with the additional robust control law, two distributed robust consensus schemes for uncertain NELSs are proposed for two cases of time-varying communication and input delays respectively, which can fully guarantee to constrain the output consensus error within a safety region simultaneously. Furthermore, numerical simulation examples are provided to demonstrate the comparable potential advantages of the proposed robust control law over some existing algorithms, including adaptability, stability, and robustness, as well as delay effects. • An NN-based robust controller is designed to effectively handle the uncertainty of NELSs. • Combining NN with BLF ensures the adaptability, stability, and robustness of the consensus tracking scheme for NELSs. • A unified analytical framework is developed by deriving upper bounds on the allowed values of communication and input delays. [ABSTRACT FROM AUTHOR]

In various applications in the field of control engineering, the estimation of the state variables of dynamic systems in the presence of unknown inputs plays an important role. Existing methods require the so-called observer matching condition to be satisfied, rely on the boundedness e variables or exhibit an increased observer order of at least twice the plant order. In this article, a novel observer normal form for strongly observable linear time-invariant multivariable systems is proposed. In contrast to classical normal forms, the proposed approach also takes the unknown inputs into account. The proposed observer normal form allows for the straightforward construction of a higher-order sliding mode observer, which ensures global convergence of the estimation error within finite time even in the presence of unknown bounded inputs. Its application is not restricted to systems which satisfy the aforementioned limitations of already existing unknown input observers. The proposed approach can be exploited for the reconstruction of unknown inputs with bounded derivative and robust state-feedback control, which is shown by means of a tutorial example. Numerical simulations confirm the effectiveness of the presented work. [ABSTRACT FROM AUTHOR]

Over the years, the systematic search for stiff model solvers that are near-optimal has attracted the attention of many researchers. An attempt has been made in this research to formulate an implicit Four-Point Hybrid Block Integrator (FPHBI) for the simulations of some renowned rigid stiff models. The integrator is formulated by using the Lagrange polynomial as basis function. The properties of the integrator which include order, consistency, and convergence were analyzed. Further analysis showed that the proposed integrator has an A-stability region. The A-stability nature of the integrator makes it more robust and fitted for the simulation of stiff models. To test the computational reliability of the new integrator, few well-known technical stiff models such as the pharmacokinetics, Robertson and Van der Pol models were solved. The results generated were then compared with those of some existing methods including the MATLAB solid solvent, ode 15s. From the results generated, the new implicit FPHBI performed better than the ones with which we compared our results with. [ABSTRACT FROM AUTHOR]

This article deals with the distributed $\mathcal {H}_{\infty }$ robust control problem for linear multiagent systems perturbed by external disturbances and norm-bounded uncertain parameters over the Markovian randomly switching communication topologies. To tackle this problem, the distributed observer-based controller is proposed, which requires the relative information between neighbors and the absolute information of a subset of the nodes, and thus is intrinsically distributed. It is of great interest to see that the distributed $\mathcal {H}_{\infty }$ robust control problem governed by such a controller can be converted to the stabilization with $\mathcal {H}_{\infty }$ disturbance attenuation problems of some decoupled linear systems, whose dimensions equal those of a single node. Then, the $\mathcal {H}_{\infty }$ stochastic robust performance region is defined to indicate the robustness of this controller against the variation of communication topologies. It is theoretically shown that the distributed observer-based controller yields bounded and connected robust performance region. Finally, the theoretical results are verified by conducting numerical simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a novel continuous-time robust direct adaptive controller for the attitude control of the three-dimensional unknown chaotic spacecraft system. It considers that the plant's nonlinear terms, exogenous disturbances, and model uncertainties are unknown and bounded; the controller design is independent of the system's nonlinear terms. These controller attributes flourish the robust performance of the closed-loop and establish smooth state vector convergence to zero. The proposed controller consists of three parts: (1) a linear controller establishes the stability of the closed-loop at the origin, (2) a nonlinear controller component that autonomously adjusts the feedback gain, and (3) a nonlinear adaptive controller compensates for the model uncertainties and external disturbances using the online estimates of bounds and model uncertainties. The output of this part remains within a given upper and lower bound. The feedback controller gain is large when the state variables are away from the origin and become small in the origin's vicinity. This feature is novel and contributes to the synthesis of smooth control effort that establishes robust fast and oscillation-free convergence of the state variables to zero. The Lyapunov direct stability analysis assures the global asymptotic robust stability of the closed-loop. Computer simulations and comparative analysis are included to verify the theoretical findings. [ABSTRACT FROM AUTHOR]

In this article, we apply the active disturbance rejection control (ADRC) to the output tracking of a class of lower triangular nonlinear systems subject to mismatched bounded stochastic disturbances of unknown statistic characteristics and nonvanishing at the origin. A major obstacle is that the paths of the stochastic disturbances are nowhere differentiable almost surely which causes that the stochastic disturbances cannot be refined into the control input channel by the usual way of state transformation. To overcome this obstacle, a set of second-order extended state observers is first designed to estimate, in real time, the disturbance in each channel, and then a backstepping ADRC based on feedforward compensation and a constructive backstepping procedure is developed, guaranteeing that the closed-loop output tracks a time-varying reference signal in practically mean square and the closed-loop states are practically bounded in probability first defined in this article. Finally, some numerical simulations are presented to validate the effectiveness of the proposed backstepping ADRC approach. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive sliding mode controller (ASMC) is proposed for an electromechanical clutch position control system to apply in the automated manual transmission. Transmission systems undergo changes in parameters with respect to the wide range of driving condition, such as changing in friction coefficient of clutch disc and stiffness of diaphragm spring, hence, an adaptive robust control method is required to guarantee system stability and overcome the uncertainties and disturbances. As the majority of transmission dynamics variables cannot be measured in a cost-efficient way, a non-linear estimator based on unscented Kalman filter (UKF) is designed to estimate the state valuables of the system. Also, a non-linear dynamic model of the electromechanical actuator is presented for the automated clutch system. The model is validated with experimental test results. Numerical simulation of a reference input for clutch bearing displacement is performed in computer simulation to evaluate the performance of controller and estimator. The results demonstrate the high effectiveness of the proposed controller against the conventional sliding mode controller to track precisely the desired trajectories. [ABSTRACT FROM AUTHOR]

This paper proposes a novel robust fixed-time control approach for the trajectory tracking control of a fully actuated marine surface vessel (MSV) subject to system uncertainties and external disturbances. First, a nominal fixed-time controller is originally designed based on the bi-limit homogeneous method. The nominal fixed-time controller can guarantee the position and velocity tracking errors converge to zero in fixed time in the absence of lumped disturbance. Then, a new type of fixed-time disturbance observer is introduced to estimate the lumped disturbance in fixed time. Finally, a robust fixed-time controller is developed by integrating the nominal fixed-time controller with the fixed-time disturbance observer. The robust fixed-time controller can guarantee the position and velocity tracking errors converge to zero in fixed time even in the presence of lumped disturbance. Benefiting from the feedforward disturbance compensation, the robust fixed-time controller has the strong robustness and excellent disturbance attenuation capability. Numerical simulations and comparisons demonstrate the effectiveness and advantages of the proposed control approach. [ABSTRACT FROM AUTHOR]

This paper investigates a finite-time backstepping control for robust stabilization of fractional-order hydroturbine governing system. We assume that the controlled system is perturbed by external disturbance, the bound of external disturbance to be unknown in advance. Through designing the virtual controllers step by step, then the appropriate actual controller is obtained. The fractional-order stability theory is used to shown the correctness of the proposed control strategy, and finally numerical simulations have been implemented to confirm the effectiveness and feasibility of the presented finitetime backsteping method. [ABSTRACT FROM AUTHOR]

The attitude control of an underactuated reusable launch vehicle (RLV) in the reentry phase involving nonminimum phase problem and control input constraints is investigated in this article. To address the nonminimum phase problem, an approach combining output redefinition and robust backstepping is proposed, where a synthetic output is constructed using the combination of the original output and the internal states to obtain stable zero dynamics, and then robust backstepping is performed on the new output. Besides, the ideal internal dynamics are obtained by using optimal bounded inversion, which are incorporated into the controller as the reference trajectories for the internal states to improve the output tracking accuracy. To cope with the control input constraints, a simple and useful anti-windup strategy is proposed by using feedback error clipping, which is shown to be very effective in mitigating control input saturation. Numerical simulations are given to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Although the literature on the a priori procedure, designed to help researchers determine the sample sizes they should use in their substantive research, is expanding rapidly, there are two important limitations. First, there is a need to expand to new popular distributions, log-normal and gamma distributions, and the present work provides those expansions. Second, there is a need to test the consequences of wrong distributional assumptions; for example, assuming a log-normal distribution when the population follows a gamma distribution, or the reverse. The present work addresses the limitations with respect to estimating population means, and it includes computer simulations, links to free and user-friendly programs that researchers can utilize for their own research, and two examples involving real data sets for illustrations of our main results. [ABSTRACT FROM AUTHOR]

Since the complexity nonlinearities generated by discontinuous control and event‐triggered scheme, fixed‐time formation in event‐based framework is a more challenging issue compared with the continuous‐time control. This paper focuses on fixed‐time leaderless formation problem for multi‐agent systems with undirected topology. We propose a distributed robust event‐triggered control strategy for the fixed‐time formation where predictor‐based state transformation is employed to deal with input delay and sliding mode technology is implemented to solve bounded disturbances. We also obtain that the upper bound of the formation settling time is only determined by delay time, control design parameters, network connectivity, and independent of the initial conditions. In addition, the lower bound for the interexecution time is calculated to ensure that there is no Zeno behavior occurs. Finally, some numerical simulations are presented to show the effectiveness of the strategies. [ABSTRACT FROM AUTHOR]

In this paper, based on event-triggered (ET) mechanisms, the problem of output tracking for a class of fractional-order uncertain systems with order 0 < α < 1 is investigated. Owing to the difficulties of measuring system full-state in practice, output tracking error is firstly used to construct an ET condition, which eventually decides whether the current signal should be transmitted. Then, by utilizing the designed error-based feedback controller, some sufficient conditions are presented to ensure that the controlled system output asymptotically tracks the reference signal. Finally, numerical simulations are performed to validate the effectiveness of the theoretical formulation. [ABSTRACT FROM AUTHOR]

A differential drive catamaran unmanned surface vehicle tracking control in presence of external disturbances and uncertainties is addressed. A super-twisting control considering a single adaptive gain is adopted, where the number of tuning parameters of this control gain is reduced compared with standard adaptive super-twisting approaches. Furthermore, the gain exhibits smooth dynamics compared with controls using discontinuous functions signals. An analysis of the closed loop stability is provided using a Lyapunov approach. The proposed adaptive super-twisting approach is designed to drive the vessel along time-varying trajectories in presence of perturbations, ensuring robustness, and practical finite-time convergence. Numerical simulations, and real-time experimental tests using a prototype, illustrate the control performance under payload uncertainty and external perturbations. For further demonstration, a comparison with some of the existing versions of the super-twisting control included one with variable gain is provided. [ABSTRACT FROM AUTHOR]

In this paper, the leader–follower robust synchronization issue is mainly addressed for reaction–diffusion neural networks (RDNNs) with multiple leaders and external disturbances under directed graphs. Based on the σ modification approach, we propose a novel distributed adaptive controller by adding a term − θ i (c i − 1) 2 to avoid the phenomenon of parameter drift, that is, the adaptive parameters grow to infinity. Meanwhile, different from the adaptive control algorithm proposed in the undirected graph, we introduce a new function χ i (t) to provide additional freedom for the design to achieve robust containment when confronted with external disturbances. Further, the robustness of tracking synchronization with one leader is guaranteed by the proposed adaptive controller when the external disturbances concerning L 2 norm are bounded. Finally, relevant numerical simulation graphics are displayed separately to verify the correctness of the related theoretical results. [ABSTRACT FROM AUTHOR]

In this article, distributed tracking control is studied for multiple Euler–Lagrange systems in the presence of external disturbances and input saturation. Specifically, full‐state constraints, input saturation, communication delays, and unmeasured velocities are all considered simultaneously. First, a novel event‐triggered scheme is developed to save the communication source and reduce computational load. Second, the anti‐saturation compensation algorithm is exploited to compensate for system saturation. Third, an adaptive law is designed to offset external disturbances. Moreover, a high‐gain observer is employed to estimate unmeasured velocities. Theorem analysis shows the stability of the closed‐loop system, and numerical simulations are provided to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

In this article, a novel robust finite‐time tracking control scheme is proposed for a class of uncertain nonlinear systems subject to the model uncertainty, external disturbance, and input saturation. A barrier function based disturbance observer (BFDO) with finite‐time convergence performance is developed to estimate the non‐smooth nonlinear compound disturbance, which includes the uncertainty, disturbance of system and input saturation. In addition, an adaptive continuous nonsingular terminal sliding mode controller, based on the barrier function and the estimate of the BFDO is developed. The Lyapunov stability and finite‐time convergence of the proposed control scheme are proved. The effectiveness and performance advantage of the proposed control scheme is demonstrated by numerical simulations and comparison with existing works. [ABSTRACT FROM AUTHOR]

The goal of this paper is to present a different approach to the analysis of the absolute stability of Lurie type systems in the single-input-single-output (SISO) case using robust control theory. The proposed technique enables the design of controllers via H ∞ mixed-sensitivity (S/KS/T), where, besides making the system absolutely stable, the performance problem can also be solved. In addition, it is also demonstrated that it is possible to make use of this new approach in time-delay Lurie type systems. Thus, through a new methodology, this work paves the way to the study of the absolute stability of multiple-inputs-multiple-outputs (MIMO) systems, aiming at a better generalization of the theory and enabling applications in other areas, such as neural networks. Examples, numerical simulations and application in Chua's circuit are given to illustrate the results. [ABSTRACT FROM AUTHOR]

The problem of decentralised robust tracking and model following is investigated for a class of uncertain large-scale interconnected systems with both any time-varying delays and any dead-zone input constraints. By combining an adaptive approach with a multiply integral inequality proposed recently in the control literature, a new design method is developed so that (i) the designed decentralised robust tracking control schemes are direct, i.e. not the complicated ones composed of two parts, which can overwhelm the dead-zone input constraints; (ii) it is unnecessary to know any information on the characteristic parameters of dead-zone functions and the time-varying delays, which makes the decentralised robust tracking control rather simple. It is also proved that the local tracking error between the output of each actual subsystem with delays and input constraints and the dynamical signals of the corresponding local reference model is uniformly exponentially bounded. Finally, a numerical example is also given to describe the design procedure and the simulations of this numerical example are implemented to demonstrate the validity of the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, we consider robust output tracking for an Euler–Bernoulli beam equation under the guidance of the internal model principle, where the disturbances in all possible channels are considered. Three typical cases are investigated in terms of different regulated outputs. The first case is based on boundary displacement output, for which only asymptotic convergence can be achieved due to the compactness of the observation operator. The second case considers two outputs of both boundary displacement and velocity. Since the control is one-dimensional, we can only arbitrarily regulate the boundary displacement and at the same time, the velocity is regulated to track the derivative of the reference. This is not the standard form investigated in the literature for robust error feedback control of abstract infinite-dimensional systems. The last case represents an extreme case that the system is non-well posed. In all the above cases, this paper demonstrates the same technique of an observer-based approach to robust control design. In the latter two cases, we can achieve exponential convergence and the closed loop is also shown to be robust to system uncertainties. Numerical simulations are carried out in all cases to illustrate the effectiveness of the proposed controls. [ABSTRACT FROM AUTHOR]

The fin field-effect transistor (FinFET) has been the mainstream technology on the VLSI platform since the 22 nm node. The silicon-on-insulator (SOI) FinFET, featuring low power consumption, superior computational power and high single-event effect (SEE) resistance, shows advantages in integrated circuits for space applications. In this work, a rad-hard design methodology for SOI FinFETs is shown to improve the devices' tolerance against the Total Ionizing Dose (TID) effect. Since the fin height direction enables a new dimension for design optimization, a 3D Source/Drain (S/D) design combined with a gate dielectric de-footing technique, which has been readily developed for the 14 nm node FinFETs, is proposed as an effective method for SOI FinFETs' TID hardening. More importantly, the governing mechanism is thoroughly investigated using fully calibrated technology computer-aided design (TCAD) simulations to guide design optimizations. The analysis demonstrates that the 3D rad-hard design can modulate the leakage path in 14 nm node n-type SOI FinFETs, effectively suppress the transistors' sensitivity to the TID charge and reduce the threshold voltage shift by >2x. Furthermore, the rad-hard design can reduce the electric field in the BOX region and lower its charge capture rate under radiation, further improving the transistor's robustness. [ABSTRACT FROM AUTHOR]

This paper proposes a new hybrid robust control method for control of an autonomous underwater vehicle. Fractional sliding mode control (FSMC) is robust against external disturbances. The main drawback of the FSMC method is creating a chattering phenomenon. Therefore, a compound control method is applied, which benefits in both robustness of the FSMC method and chattering elimination by the new control algorithm. A random noise is applied in order to verify the robustness of the proposed control method. The stability of FSMC and proposed compound control method has been verified by Lyapunov theory. The effectiveness of the proposed control method is compared with FSMC, which numerical simulation results confirm the best performance of the proposed control method. [ABSTRACT FROM AUTHOR]

This paper considers the problem of the accurate task space finite-time control susceptible to both undesirable disturbance forces exerted on the end-effector and unknown friction forces coming from joints directly driven by the actuators as well as unstructured forces resulting from the kinematic singularities appearing on the mechanism trajectory. We obtain a class of estimated extended transposed Jacobian controllers which seem to successfully counteract the external disturbance forces on the basis of a suitably defined task-space non-singular terminal sliding manifold (TSM) and the Lyapunov stability theory. Moreover, in order to overcome (or to minimise) the undesirable chattering effects, the proposed robust control law involves the second-order sliding technique. The numerical simulations (closely related to an experiment) ran for a mobile manipulator consisting of a non-holononic platform of (2; 0) type and a holonomic manipulator of two revolute kinematic pairs show the performance of the proposed controllers and make a comparison with other well-known control schemes. [ABSTRACT FROM AUTHOR]

Time delay exists in image-based visual servo system, which will have a certain impact on the system control. To solve the impact of time delay, the time delay compensation of the object feature point image and the image Jacobian matrix is discussed in this paper. Some work is done in this paper: The estimation of the object feature point image under time delay is based on a proposed robust decorrelation Kalman filtering model, for the measurement vectors which cannot be obtained during time delay in the robust Kalman filtering model, a polynomial fitting method is proposed in which the selection of the polynomial includes the position, velocity and acceleration of the object feature point which impact the feature point trajectory, then the more accurate object feature point image can be obtained. From the estimated object feature point image under time delay, the more accurate image Jacobian matrix under time delay can be obtained. Simulation and experimental results verify the feasibility and superiority of this paper method. [ABSTRACT FROM AUTHOR]

A systematic approach is developed for determining a control input for the point-to-point control of an overhead crane that exhibits temporal variation of rope length in addition to damping and nonlinearity, without inducing residual vibration. Complete suppression of the residual vibration is achieved by eliminating the natural frequency component of the cargo from the apparent external force, which is defined to include the effects of damping, nonlinearity, and parameter variation. Furthermore, an effective technique previously proposed by the authors for improving robustness to the modeling error of the natural frequency is extended. Numerical simulation results show that, even when cargo is hoisted up or down during operation, the proposed method realizes accurate positioning of the cargo without inducing residual vibration and sufficiently improves robustness. To the best of our knowledge, this is the first frequency-domain robust open-loop control strategy that ensures a theoretical zero amplitude for residual vibration in the absence of modeling error in nonlinear crane hoisting operation. The developed method is not only a contribution to the realization of low-cost and efficient crane hoisting operation, but is also applicable to the control of other nonlinear damped systems that include time-varying parameters. [ABSTRACT FROM AUTHOR]

A low-conservative composite nonlinear feedback controller is proposed for singular time-delay systems with time-varying delay. The proposed composite nonlinear feedback controller not only improves the transient responses of the closed-loop system but it also has less conservatism than other composite nonlinear feedback controllers. The gain of the linear part of the composite nonlinear feedback controller is obtained by precise mathematical calculation to depend not only on the upper bound of the delay but also on the delay range and rate of its changes. More advantages of the proposed composite nonlinear feedback controller are its accurate operation in the presence of actuator saturation, model uncertainties, and system singularities. The linear and nonlinear parts of the proposed controller are designed by solving a linear matrix inequality problem confirmed through a theorem using Lyapunov stability analysis. The theoretical achievements are endorsed by computer simulation through numerical and practical examples. [ABSTRACT FROM AUTHOR]

This paper addresses the trajectory tracking control problem of a planar vertical take-off and landing (PVTOL) aircraft in the presence of position constraints and external disturbances. A novel robust constrained control approach is proposed by incorporating the barrier Lyapunov function (BLF) and nonlinear damping items within the framework of dynamic surface control design. The dynamic surface control is used to avoid the 'explosion of terms' problem of the traditional backstepping control. The tan-type BLF is utilised to preserve the position tracking errors always within the predefined position constraints. The nonlinear damping items are applied to handle the effect of external disturbances. The uniform ultimate boundedness of the resulting closed-loop system is rigorously proved through the Lyapunov's direct method. A distinct feature of the proposed control approach is that it is a general methodology for the trajectory tracking control of PVTOL aircraft with or without position constraints. Both theoretical analysis and numerical simulations illustrate the effectiveness and benefits of the proposed control approach. [ABSTRACT FROM AUTHOR]

This paper designs a predefined-time convergent continuous control algorithm to stabilize a permanent-magnet synchronous motor (PMSM) system. Three cases have been considered: disturbance-free, in presence of a deterministic disturbance satisfying a Lipschitz condition, and in presence of both a stochastic white noise and a deterministic disturbance satisfying a Lipschitz condition. The designed control law is free from the restrictions of exponential control growth and exact initial conditions knowledge. This is the first predefined-time convergent continuous control algorithm applied to stabilizing a PMSM system with both deterministic and stochastic disturbances, which enables one to a priori set the predefined convergence time even in presence of various disturbances of different nature. Numerical simulations are provided for a PMSM system to validate the obtained theoretical results in each of the three considered cases. The simulation results demonstrate that the employed values of the predefined-time convergent control inputs are applicable in practice. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive robust boundary controller is designed for an unstable heat equation with external disturbance flowing into the control end. The disturbance and uncertainty effect is cancelled out in the closed-loop system by using on-line approximation of disturbance upper-bound provided as an output of adaptive robust update law. The asymptotic stability of the controlled system in the presence of unknown disturbance and/or parametric uncertainties is proved utilising the Lyapunov theorem. Unlike previous researches, the control implementation does not require prior knowledge of unknown disturbance. Moreover, the controller does not require measuring the system states or estimating the system states by an observer. The adaptive robust controller can be regarded as a combination of the best qualities of the adaptive controller and the robust controller with no prior knowledge of system uncertainty, and asymptotic tracking error performance. Numerical simulations and comparisons are provided to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

We consider adaptive optimal tracking problems for a minimum-phase discrete-time plant with uncertainty in the output channel and bounded exogenous disturbance. The coefficients of the equation of the linear time-invariant nominal model, the uncertainty gain, and the upper bound of the exogenous disturbance are assumed to be unknown, and the worst-case asymptotic tracking error serves as the performance criterion. It is shown that the statement of the optimal problem depends on a priori information about the bounded control. The solution of the problems is based on the polyhedral estimation of all unknown parameters and the use of the performance factor of the tracking problem as an identification criterion for calculating the current optimal estimates. The performance and efficiency of the proposed control algorithms is illustrated by the results of numerical simulation. [ABSTRACT FROM AUTHOR]

This article studies the event‐triggered control problem for nonlinear systems that are merely integral input‐to‐state stable (iISS) with respect to measurement errors and external inputs. By using the iISS Lyapunov function, which comes from a necessary and sufficient condition on iISS, an integral‐based event‐triggering mechanism is introduced to compensate the effects of measurement errors. Under some assumptions on the gains of the iISS Lyapunov function, both the closed‐loop iISS and Zeno‐freeness are proved when the external inputs are measurable. In the presence of unknown disturbances, a novel switching event‐triggering mechanism is designed based on the relationship between the transmitted state and some threshold constant. Subsequently, the corresponding lower bound of inter‐event times is given explicitly to ensure Zeno‐freeness. It is shown that the proposed switching mechanism can be applicable to the nonlinear systems where some existing event‐triggering mechanisms are invalid in avoiding Zeno behavior. Finally, numerical simulations are provided to illustrate the efficiency and feasibility of the obtained results. [ABSTRACT FROM AUTHOR]

In this article, we propose a networked control architecture to ensure the plant's safety in the presence of cyber‐attacks on the communication channels. In particular, we consider systems subject to both state and input constraints that must be preserved for safety reasons despite any admissible attack scenario. To this end, first, two different detectors are proposed to detect attacks on the setpoint signal as well as on the control inputs and sensor measurements. Then, an emergency controller (EC), local to the plant, is designed to replace the networked controller whenever an attack is detected. Finally, the concept of robust N‐step attack‐safe region is introduced to ensure that the EC is activated, regardless of the detector performance, at least one‐step before the safety constraints are violated. It is formally proved that the plant trajectory is uniformly ultimately bounded in an admissible region regardless of the attacker's actions and duration. Finally, by considering a continuous‐stirred tank reactor system, numerical simulations are presented to show the proposed solution's capabilities. [ABSTRACT FROM AUTHOR]

A control architecture for robust biped navigation that takes into account traversability on terrain, foot-reachability, and capturability all at once in dynamic situations is proposed. It consists of online mapping of terrain and quick decision of foot placement. A grid map with elevation, normal direction and the standard deviation of measurement is proposed for the former and is named the stochastic Elevation-and-Normal Grid (ENG) map. It is incrementally updated as depth sensor information comes in every cycle. The traversability of each grid can be easily checked based on the associated information. The latter stands upon the canonical biped track (CBT), which is a pair of continuous paths that the feet track. It is drawn along a nominal collision-free path on the ENG map. The most efficient foot placement at the next step from the viewpoint of the foot-reachability is chosen on them as the initial candidate, around which a feasible placement accommodated with traversability and capturability is found by the breadth-first search. An autonomous biped locomotion system is completed by combining the above architecture with a foot-guided controller based on the terminal capturability. The efficacy of the proposed method was validated through some computer simulations. [ABSTRACT FROM AUTHOR]

In this paper, chaotic synchronization with uncertainties and disturbances is studied. Firstly, a new control method based on UDE control is proposed, which is composed of two controllers: one is the stabilization controller in order to realize the stabilization of nominal system without uncertainties and disturbances and the other is the UDE controller in order to deal with the given controlled system with both uncertainties and disturbances. Then, two examples are studied by the above method. Finally, the correctness and effectiveness of the method are verified by numerical simulation. [ABSTRACT FROM AUTHOR]

This paper is dedicated to the robust nonlinear control of friction-induced vibrations (FIV), more particularly those generated according to the mode-coupling mechanism. A nonlinear scheme which consists of a sliding-mode controller implemented by using a high-gain state observer is proposed. The main objective is to suppress or mitigate the generated vibrations by taking into account of the nonlinearities and uncertainties inherent to friction systems. Hence, this study proposes the analysis of the closed-loop performances of the high-gain observer-based sliding-mode controller when used for the active control of vibrations issued from the mode-coupling mechanism. Based on numerical simulations, the proposed controller has shown suitable performances distinguished from an effective suppress of the generated vibrations. Otherwise, it is shown that the gain of the used nonlinear state observer must be tuned in order to ensure a suitable compromise between the robustness level of the performances with respect to parameter uncertainty and the robustness level with respect to the measurement noise. [ABSTRACT FROM AUTHOR]

Understanding under which conditions physical systems thermalize is a long-standing question in many-body physics. While generic quantum systems thermalize, there are known instances where thermalization is hindered, for example in many-body localized (MBL) systems. Here we introduce a class of stochastic collision models coupling a many-body system out of thermal equilibrium to an external heat bath. We derive upper and lower bounds on the size of the bath required to thermalize the system via such models, under certain assumptions on the Hamiltonian. We use these bounds, expressed in terms of the max-relative entropy, to characterize the robustness of MBL systems against externally-induced thermalization. Our bounds are derived within the framework of resource theories using the convex split lemma, a recent tool developed in quantum information. We apply our results to the disordered Heisenberg chain, and numerically study the robustness of its MBL phase in terms of the required bath size. The thermalization of many-body localization phases poses a number of open questions related to our understanding of thermalization in quantum systems. Here, the authors aim to demonstrate that a quantum information approach can be used to investigate the mechanisms of thermalization in a quantum many-body system when coupled to an external system. [ABSTRACT FROM AUTHOR]