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This work proposes a resource efficient robust control scheme for missile-target engagement scenarios subjected to external disturbances. The robustness is achieved by using an annular event-triggered artificial time-delayed control (ET-TDC) methodology with input saturation. The ET-TDC philosophy uses the TDC strategy through a dynamic predefined triggering mechanism which overcomes the requirement to update the control periodically for every sampling instant, unlike conventional TDC and other robust control schemes. Thus the proposed methodology can tackle uncertainties with minimal a-priori knowledge while significantly reducing the over-utilisation of system resources. In addition, the adopted event-triggered mechanism facilitates further conservation of energy which might be crucial for mid-to-long range engagement scenarios. The closed-loop stability is derived analytically and the simulation results illustrate the efficacy of the proposed guidance framework in comparison with other state-of-art robust control methodologies. [ABSTRACT FROM AUTHOR]

This paper focuses on finite-time adaptive practical tracking control for a class of high-order nonlinear systems with full-state constraints and input saturation. The state constraints are handled by applying nonlinear transformed functions (NTFs) and the input saturation is estimated by an auxiliary hyperbolic tangent function. On the basis of adding a power integrator technique and adaptive control method, an adaptive state feedback controller is designed for the closed-loop system. With the aid of finite-time stability theory, the tracking error converges to a bounded neighbourhood of the origin in a finite time, and all the signals in the closed-loop system are bounded. At last, a simulation example and a practical example are presented to show the effectiveness of the proposed control procedure. [ABSTRACT FROM AUTHOR]

The present study focuses on controller design for high-order fully actuated systems that experience input saturation and are affected by bounded disturbances, such as nonlinear uncertainties and time-varying unknown parameters. A saturated adaptive controller is developed via the fully actuated system approach and the Lyapunov stability theory to achieve output control and reject disturbances. The disturbances are treated as an extended state and then estimated by introducing an extended state observer. An adaptive variable is used to handle the estimation error between the actual and estimated values of the disturbances. An auxiliary system is designed to mitigate the saturation effect. Lyapunov's direct method verifies that the estimation error, the tracking error, the adaptive state, and the auxiliary system state will eventually stabilise within a bounded ellipsoid. An illustration of spacecraft attitude control demonstrates the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper explores the application of a fully actuated system (FAS) approach to a spacecraft rendezvous system with actuator saturation. A FAS model for the spacecraft rendezvous system is developed, followed by the design of an extended state observer (ESO) to estimate unmeasurable states and the system's nonlinear terms. The saturation issue is addressed using the convex hull method. By the designed ESO, a state feedback controller for the system is designed using the FAS approach, resulting in a constant linear closed-loop system whose eigenvalues can be arbitrarily assigned. This method simplifies the controller design process and provides a more accurate system model without the linearisation of nonlinear terms, thereby improving control accuracy. Simulation results show the effectiveness and usefulness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, the adaptive control problem is investigated for a class of interconnected nonlinear systems (INS) with unknown interconnection delays and input saturations. For state unmeasurable problem, a full dimension state observer (SO) is designed to estimate the inaccessible state variables. Broad learning system (BLS), a novel nonlinear approximation technique, is introduced in this study to identify the unknown dynamics and could achieve better approximation performance. An adaptive distributed control (DC) scheme is proposed for the uncertain time-delay INS without input saturation, which guarantees that the stability of the closed loop INS. On this basis, the input saturation problem is further considered, an online approximation smooth function is added into the distributed adaptive tracking controller, such that the closed-loop INS have the anti-input saturation capability. In terms of Lyapunov theory, all the signals in the closed-loop uncertain time-delay INS with input saturation are proved to be uniformly ultimately bounded (UUB) and the tracking errors could converge to a small neighbourhood of zero. Finally, one simulation example performed on two parallel inverted pendulum cars demonstrates the superiority of the developed distributed control scheme. [ABSTRACT FROM AUTHOR]

A novel integrated guidance and control scheme is derived for STT missile with strict constraints as desired impact angle, input saturation and partial system state in three-dimensional space. The backstepping technique and command filter are adopted for achieving input constraints, and the improved compensation signals are constructed to correct tracking errors. The integral barrier Lyapunov function is introduced to prevent the partial system states from exceeding a predefined interval. A modified extended state observer is employed to strengthen the robustness of the system further. Theoretically, the required properties of a closed-form system are proved by Lyapunov theory in detail. Numerical simulations are conducted to exhibit the performance and robustness of the IGC scheme fully. [ABSTRACT FROM AUTHOR]

This research aims to design a robust adaptive tracking controller for Chua's switched nonlinear circuit systems. The proposed adaptive composite nonlinear approach is modified in order to provide a robust controller with improved performance in the presence of uncertainties and input saturation. It is demonstrated that by employing an integral sliding mode controller that is based on a linear matrix inequality (LMI), the resultant closed-loop system can attain an exponentially boundedly stable. This technique ensures robustness to the impacts of uncertainties and input saturation and reduces the chattering phenomenon. Eventually, a simulation example of Chua's circuit system is utilised to reveal the performance and advantages of the offered approach. [ABSTRACT FROM AUTHOR]

In this article, a flexible performance constraint-based tracking control scheme is proposed for the anti-swing control of a quadrotor UAV-suspended payload system under external disturbance and input saturation. By applying system coupling relations and positive system theory, a self-regulating auxiliary system is constructed to generate correction signals to achieve the ability to regulate a prescribed performance function. The disturbance interval observer is employed to estimate the unknown disturbance. The interval width of the disturbance is used to design a continuous robust signal, enhancing the system's robustness. Additionally, it is with the intention of designing the controller for the under-actuated system to achieve effective tracking that the backstepping control scheme is used. It can always track the reference signal and satisfy flexible performance constraints based on theoretical analysis. Finally, the effectiveness of the proposed scheme is verified by experimental studies. [ABSTRACT FROM AUTHOR]

This paper proposes a finite-time dynamic surface control (FTDSC) scheme using a novel nonlinear filter for nonlinear systems with input saturation and output constraint. The FTDSC scheme featured by nonlinear filter is presented to overcome the drawback of the traditional DSC scheme using first-order linear filter. The barrier Lyapunov function (BLF) is used to handling output constraint and the disadvantage of conventional input saturation problem is solved through introducing a nonlinear smooth function. In order to deal with the impact of external disturbance, the nonlinear disturbance observer (NDO) is introduced to estimate the disturbance. It is proved that All signals are semi-globally uniformly ultimately bounded (SGUUB) in the closed loop system. Moreover, the tracking error can convergences to a neighborhood of zero through the proper designed parameters. Comparison studies are conducted to verify that the proposed FTDSC scheme comparing with the traditional DSC scheme has the more accurate tracking capability. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the problem of designing locally stabilizing dynamic output feedback controllers and estimate the domain of attraction for discrete-time Takagi-Sugeno (T-S) fuzzy systems. A realistic scenario is assumed where the control signal is subject to saturation, and the premise variables are partially or completely unmeasured, that is, not available for the control law. As a result, the fuzzy output controller can have a different number of fuzzy rules and a different set of membership functions from the T-S model. To obtain locally stabilizable conditions, we propose modeling the variation rate of the membership functions without using upper bounds, a new contribution in the context of output control of discrete-time T-S systems. The design conditions are expressed as linear matrix inequality relaxations based on fuzzy Lyapunov functions using slack variables introduced by Finsler's lemma. Numerical examples illustrate the effectiveness of the approach. [ABSTRACT FROM AUTHOR]

In this manuscript, the regulation of one degree-of-freedom Euler–Lagrange systems subject to input saturation is addressed. In particular, the design and analysis of a nonlinear static state feedback controller is presented. As a result, it is proven via Lyapunov's direct method that, in the presence of Rayleigh dissipation, the closed-loop equilibrium point is globally asymptotically stable with a strict Lyapunov function. Since saturation occurs in the system which contains the actuator model, the proposed control law is unconstrained and can be simplified to a proportional-derivative with desired gravity compensation algorithm. As a by-product global asymptotic stability is also proven for the case where Rayleigh dissipation is null. Numerical simulations on a crank-slider mechanism are presented. Moreover, experimental results on a DC-DC buck power converter are also shown and confirm the viability of our approach. [ABSTRACT FROM AUTHOR]

In this paper, novel practical finite-time robust adaptive controllers are investigated for a 5-link single support phase (SSP) lower limb biped robot subjected to unknown physical and dynamical parameters, disturbances, and unknown input saturation. The developed adaptive approaches are based on a terminal sliding surface and a finite-time stability analysis to design controller and adaptation laws. The adaptive mechanisms deal with estimating unknown terms, the upper bound of the unknown term vector, or estimating the unknown limits of input saturation. Consequently, the proposed approach is applicable when the physical and dynamical parameters of the robot and the saturation input parameters are not known. In addition, the Lyapunov stability approach warranties that the tracking errors are robust finite-time uniformly ultimately bounded and provides the practical finite-time stability of the closed-loop system. Finally, numerical simulations are provided to show the feasibility, effectiveness, and performance enhancement of the proposed methods over state-of-the-art methods. [ABSTRACT FROM AUTHOR]

This article is committed to studying the tracking control problem for a class of uncertain nonlinear system with unknown control coefficients. The system is subject to full-state constraints, input saturation constraint, and external disturbances simultaneously. By introducing a hyperbolic tangent function to approximate the saturated input function, the sharp corner caused by the input saturation is avoided. In the meanwhile, an auxiliary system is constructed to compensate the approximation error. By using the barrier Lyapunov function based adaptive backstepping control, the Nussbaum-type adaptive controllers are constructed for the augmented system with unknown control direction. It not only ensures the system states are always within the constrained range, but also guarantees the tracking performance of the system, no matter whether the control direction of the system is known or not. Meanwhile, dynamic surface control is used in the controller design, which avoids 'computation explosion' caused by the repeated derivation of virtual control law. It improves the tracking performance of the system and reduces the burden of the controller greatly. Finally, a simulation example is given to demonstrate the effectiveness of the proposed control scheme in three scenarios. [ABSTRACT FROM AUTHOR]

This paper proposes a novel prescribed-time cooperative guidance law (PTCGL) for multiple missiles cooperatively attacking a manoeuvring target. Guidance models in two directions are used and the acceleration saturations are also considered in both two directions. In line-of-sight (LOS) direction, by applying prescribed-time multi-agent consensus theory, the problem of the times-to-go ( T g o s ) of multiple missiles converging to a same value is transformed into a stabilisation problem. Then the cooperative guidance law in LOS direction is designed based on the prescribed time integral sliding mode surface (PTISMS) and a new variable coefficient exponential reaching law, and a first-order auxiliary system is introduced to deal with the input saturation problem; based on a prescribed time linear sliding surface (PTLSMS), the cooperative guidance law in normal LOS direction is designed to ensure the LOS angle and LOS angle rate convergence within a prescribed time, and a second-order auxiliary system is designed to deal with the input saturation problem. Furthermore, the prescribed time convergence of the PTCGL is proved with the Lyapunov stability theory. Finally, numerical simulations demonstrate the effectiveness and advantages of the proposed PTCGL. [ABSTRACT FROM AUTHOR]

This paper is concerned with reset control and L 2 -gain stability of piecewise-affine systems with input saturation and external disturbance under the framework of hybrid systems. Firstly, we present a reset controller and establish exponential stability conditions of piecewise-affine systems with input saturation under the reset controller. Secondly, sufficient conditions for L 2 -gain stability of the closed-loop systems with input saturation and external disturbance are provided and a reset controller is designed to enhance the L 2 -gain performance of piecewise-affine systems with input saturation. Furthermore, robustness to inflations of the flow and jump sets is established. Finally, a numerical simulation is provided to illustrate the results. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to design an adaptive controller for uncertain strict-feedback stochastic nonlinear systems with dead zone and input saturation. A barrier Lyapunov function in asymmetric forms is constructed which can relax the requirements for initial conditions. To simplify the design process of the controller, a dead zone-based model of saturation is implemented and neural networks are used to approximate uncertain nonlinear functions and to construct an observer to cope with difficulties raised by the presence of immeasurable state variables. By applying the backstepping technique, a smooth tracking controller with adaptive law is proposed to ensure all the signals in the closed-loop system are semi-globally uniformly ultimately bounded. Furthermore, the tracking error can converge to a small neighbourhood of the origin. The effectiveness of the proposed scheme is presented by simulations on a numerical example. [ABSTRACT FROM AUTHOR]

This paper investigates the synchronization control problem for a supply vessel during underway replenishment with unknown dynamics, unknown disturbances, input saturation and unavailable velocities. A virtual trajectory shifted by a distance at an angle relative to the trajectory of the supplied vessel is planned. A high-gain observer observer is employed to estimate unavailable vessel velocities and an auxiliary design system is constructed to address the effect of input saturation. Then, the adaptive radial basis function neural networks are employed to approximate unknown dynamics and the adaptive laws are derived to estimate bounds of unknown disturbances. Incorporating the above into the dynamic surface control method, an output feedback robust adaptive neural synchronization control law is developed to force the supply vessel to track the virtual trajectory such that the synchronization navigation between the supply and the supplied vessels is realized. The theoretical analysis and simulation results validate our developed control scheme. [ABSTRACT FROM AUTHOR]

The problem of event-triggered control for discrete-time piecewise-affine systems subject to input saturation and bounded disturbance is investigated in this paper. An LMI-based event-triggered controller is designed to guarantee the local asymptotic stability by introducing auxiliary feedback matrices to handle input saturation. In addition, the region of attraction is well estimated. Meanwhile, by synthesising the feedback control gains and the given event-triggering condition, an optimisation problem for maximising the region of attraction is formulated in LMIs. For input-saturated piecewise-affine systems with bounded disturbance, our control objective is to reduce the influence of disturbance while reducing communication in order to guarantee that the system is uniformly ultimately bounded. The effectiveness and advantages of the proposed approaches are demonstrated by simulations. [ABSTRACT FROM AUTHOR]

This work considers a finite-time command filtered course tracking problem of ships with unknown bounded disturbances, unmodelled dynamics and input saturation. By melting command filter technique into backstepping design, a finite-time control scheme is proposed, which overcomes the 'explosion of complexity' and 'singularity' problems resulted from the calculation of repeated derivatives of virtual control inputs in the conventional backstepping method. A hyperbolic tangent function is adopted to estimate saturation with a bounded estimation error in order to guarantee that the saturation function acting on the rudder angle can be differentiable, where the rudder angle is considered as a new state variable whose initial value is zero. The finite-time disturbance estimator is constructed to provide the estimation of compounded uncertain item derived from unmodelled dynamics and external disturbances. Simulation results and comprehensive comparisons are used to demonstrate the effectiveness and superiority of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Input saturation is very important for the analysis and design of control system. Ignoring the input saturation will have an adverse effect on the control system, and even cause the control system to be unstable. In practice, almost all the control systems are affected by input saturation, involving switched systems, multi-agent systems, robot systems and spacecraft rendezvous systems, etc. In the past few decades, a large number of research results have been obtained on input saturation. This paper attempts to give an overview through a bibliometric analysis based on the publications related to input saturation which were published from 2010 to 2020 and retrieved from the Science Citation Index Expanded database. We give a detailed discussion based on countries, institutions, research areas, journals, authors and author keywords. The main results show that Automatica takes the leading position among the top 10 academic journals, followed by International Journal of Robust and Nonlinear Control and IEEE Transactions on Automatic Control. China ranks a leading position in this field, followed by the United States and France. Harbin Institute of Technology has the topmost total articles, citations and h-index. The future research works are highlighted and we summarise the conclusion in end. [ABSTRACT FROM AUTHOR]

This paper investigates the robust perimeter control for two urban regions with sampled-data and input saturation. Based on the macroscopic fundamental diagram, an uncertain network vehicle balance model is established for two urban regions. Instead of the continued feedback control, this paper designs a sampled-data feedback control law to stabilize the traffic accumulations at the desired state. Based on the Lyapunov function theory, the stability condition of two urban regions is given in the form of linear matrix inequalities (LMIs), which ensures that the traffic accumulation for each region is stabilized at the desired state. Moreover, for the inevitable disturbances, the robust saturation control strategy is designed such that the traffic accumulation for each region is robustly stabilized at the desired state, and meanwhile a less disturbance attenuation level is guaranteed. Numerical examples are given to illustrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper investigates the adaptive tracking control problem of uncertain large-scale nonlinear time-delay systems with input saturation. Unknown constants and continuous functions with respect to output or delayed output are allowed in the nonlinear interconnected functions. The dynamic gain control technique is used to study the tracking control problem of considered system, which simplifies design process and form of controller. By introducing a full-order state observer and three dynamic equations, output feedback tracking control scheme is constructed to ensure that all signals of the closed-loop system are globally uniformly ultimately bounded (GUUB). In addition, the tracking error can converge to a small neighbourhood around the origin by selecting appropriate parameters. Finally, a practical example is presented to illustrate the feasibility of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper studies the fuzzy decentralised control issue for the fractional-order interconnected nonlinear systems with input saturation. The fuzzy logic systems (FLSs) and piecewise functions are used to approximate unknown nonlinear continuous functions and the input saturation of the considered systems. Under the frameworks of the backstepping control design technique and adaptive fuzzy decentralised control theory, an adaptive fuzzy decentralised control strategy is proposed. In view of fractional-order Lyapunov stability theory, it confirms the stability of the control plants and the convergence of the tracking errors. Finally, two simulation examples are applied to confirm the practicability and validity of the presented control strategy, in which, one is the two-order numerical fractional-order large-scale systems, the other one is the fractional-order permanent magnet synchronous motor (PMSM) model. [ABSTRACT FROM AUTHOR]

In this paper, a redesigned approximate dynamic inversion (RADI) method is developed for a class of pure-feedback nonaffine-in-control nonlinear systems (PFNNSs). Recently, the approximate dynamic inversion (ADI)-based algorithms have been widely implemented for nonaffine-in-control nonlinear systems. To employ ADI-based methods, a fast dynamic subsystem has to be established to derive the explicit inversion of the nonaffine equation. However, the previous research on ADI rarely considers that the amplitude of actual input derived from the fast augmented subsystem can be extremely high, which maybe intolerable for practical systems. In this paper, we set up input saturation and view the difference between input with and without saturation as a perturbation. Then, an intermediate subsystem is constructed to compensate the influence of this perturbation by approximating its inversion. The exponential stability of the overall closed-loop system is ensured via singular perturbation theorem. Numerical examples are provided to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, we propose an adaptive tracking dynamic surface back-stepping control based on Nussbaum disturbance observer for uncertain high-order strict-feedback MIMO nonlinear systems with external disturbances, unknown parameters and modelling uncertainties. It is assumed that the control action is affected by input saturation; so to compensate the resulted undesirable effects, the tanh(.) function is used as an approximation to the saturation function. To tackle the unknown external disturbances and uncertainties, a Nussbaum disturbance observer is proposed. Moreover, an appropriate adaptive law is presented to deal with the unknown parameters. Then, the dynamic surface control method is used to overcome the inherent problem 'explosion of complexity' that appeared in the conventional back-stepping method. The Lyapunov stability analysis proves that the closed-loop system is semi-globally uniformly bounded. At last, reasonable effectiveness and applicability of the adaptive tracking dynamic surface control are illustrated by simulation results. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of practical stabilisation of arbitrary reference trajectories, including time-varying trajectories and fixed points for underactuated ships subjected to input saturation and parametric modelling uncertainties. Two novel coordinate transformations are introduced to deal with the problems caused by the non-zero off diagonal terms in the inertia matrix and the underactuation, respectively. Based on the backstepping technique, the dynamic surface control method and the Lyapunov's direct method, a saturated robust adaptive controller is designed to achieve practical convergence of tracking errors to a bounded area centred at zero. Some comparative simulations are performed to illustrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of consensus in multi-agent systems. The consensus is investigated considering directed networks composed by identical agents described by linear models of arbitrary order, subject to input saturation and non-uniform time-varying delays. The main results are sufficient conditions for consensus analysis and design of distributed consensus protocols for multi-agent systems. In addition, because the saturation might prevent the multi-agent system to attain consensus on some set of initial conditions, it is also proposed a strategy to calculate a region in which the consensus is guaranteed. The results follow from the Lyapunov–Krasovskii theory and are formulated in the linear matrix inequalities (LMIs) framework. Finally, we present examples to illustrate the effectiveness of the proposed method in contrast with similar approaches existing in the literature. [ABSTRACT FROM AUTHOR]

This paper investigates the semi-global stabilisation problem of high-order nonlinear systems with full-state constraints and input saturation. By constructing the high-order barrier Lyapunov function (BLF) and auxiliary subsystem, a state feedback controller is designed without state and input constraints violation. It is proved that all the closed-loop signals are bounded in the semi-global sense, error signals converge to a small neighbourhood of the origin, and full-state constraints and input saturation are not violated. Two simulation examples are presented to show the feasibility and advantage of this method. [ABSTRACT FROM AUTHOR]

This paper considers the dynamic output-based event-triggered strategy design for linear systems subject to input saturation. The dynamic event-triggered control reduces the communication burden, and a minimum inter-event time is explicitly provided to exclude Zeno behaviour. A dynamic linear anti-windup augmentation is presented to deal with the input saturation. For the given anti-windup compensator, a criterion is formulated to achieve practical stability with finite L 2 gain. Moreover, an algorithm with projection lemma is proposed to design the anti-windup augmentation when it is unknown. For two special cases, i.e. the anti-windup compensator is static or of the plant-order, the feasibility conditions become convex. Simulations are given to illustrate the theoretical results. [ABSTRACT FROM AUTHOR]

This paper reviews the latest developments in anti-disturbance control of switched systems subject to input saturation. Firstly, the research significance of switched system, input saturation and anti-disturbance control is discussed, respectively. The significance of these researches is to realize the solution of the problems existing in practical engineering. Then it introduces the research status and development of dynamic analysis at home and abroad, including the research status of system control under input saturation constraints and the research status of anti-disturbance control of switched systems with input saturation. [ABSTRACT FROM AUTHOR]

By considering non-repetitive uncertainties, an observer-based data-driven iterative learning control (ObDDILC) is proposed in this article for non-linear non-affine systems in the existence of non-repeatable disturbances, random initial values, and input constraints. Aiming to addressing the non-affine and non-linear characteristics of the systems, a linear data model (LDM) is constructed in iteration domain without introducing any physical interpretation but only for the purpose of the subsequent algorithm design and analysis. The iteration-varying initial values and disturbances are incorporated as a total non-repetitive uncertainty of the LDM. Both an iterative learning observer and a parameter estimator are proposed to address the total non-repetitive uncertainties and unknown parameters of the established LDM, respectively. Then, an observer-based learning control law is developed using the estimated output to compensate the impact of the non-repetitive uncertainties on the control performance, where a saturated function is employed to deal with the input constraints. The convergence of proposed ObDDILC is proved by using contraction mapping as the basic tool. All of the algorithms are designed and analysed without dependence of any model information except I/O data. The theoretical results are tested by simulations. [ABSTRACT FROM AUTHOR]

This paper studies the global asymptotical stabilisation and H ∞ control problems for a class of nonlinear Hamiltonian singular systems (NHSSs) with time-varying delays as well as input saturation. The delays existing in input and output are assumed to be bounded. A global asymptotic stabilisation controller is first proposed by output feedback, and H ∞ control performance is achieved for the discussed system when external disturbances are considered. Based on the structural characteristic of the NHSSs, the closed-loop system under the output feedback controller is transformed equivalently into slow subsystem and fast subsystem. Different criterions are identified to guarantee that the resulting closed-loop system is asymptotically stable and the γ-dissipative inequalities holds in the presence of disturbances, respectively. Finally, the validity of our proposed results is illustrated by a numerical example. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of adaptive fault tolerant tracking control for uncertain nonlinear systems in the event of external disturbances, actuator faults and input saturation. In order to guarantee the transient and steady-state control performance, the prescribed performance function is employed to impose the anticipant performance criterion on the output tracking error. By using the error transformation, the original inequality error constraint is converted to an unconstrained issue. For the conversion systems, the negative effect resulting from the external disturbances is restrained via the adaptive control approach. The radial basis function neural network (RBFNN) is adopted to handle the unknown nonlinear functions. The Nussbaum gain technique is utilised to deal with the nonlinear terms arising from the actuator faults and input saturation. Combining with the backstepping control strategy, an adaptive neural fault tolerant control (FTC) scheme is developed for the uncertain nonlinear systems. It is rigorously proved that the proposed controller is capable of ensuring the boundness of all closed-loop signals as well as the specified tracking performance. Simulation results on two examples are given to illustrate the effectiveness of the presented control approach. [ABSTRACT FROM AUTHOR]

This paper focuses on composite nonlinear feedback (CNF) controller design for tracking control problem of strict-feedback nonlinear systems with input saturation to address the improvement of transient performance. First, without considering the input saturation, a stabilisation control law is designed by using standard backstepping technique for the nonlinear system, then a feedforward control law is added to the backstepping-based stabilisation control law to construct a tracking control law. The tracking control law is tuned to drive the output of the closed-loop system to track a command input with quick response. Then, an additional nonlinear feedback law is constructed and combined with the tracking control law to obtain a CNF control law. The role of this additional nonlinear feedback law is to smoothly change the damping ratio of the closed-loop system while the system output approaches the command input, and to reduce overshoot caused by the tracking control law. It is shown that the extra-adding nonlinear feedback part does not cause the loss of stability of the closed-loop system in its attractive basin. [ABSTRACT FROM AUTHOR]

In this paper, we study the global finite-time consensus tracking problem for uncertain second-order multi-agent systems subject to input saturation. The communication graphs are allowed to be general directed graphs. Sliding-mode observer-based distributed controllers are proposed such that global finite-time consensus tracking is achieved with bounded control inputs. Only relative state or output measurements are used in the proposed controller which reduces the communication requirement on the agents. Simulation examples are given to illustrate the effectiveness of the proposed control strategies. [ABSTRACT FROM AUTHOR]

This paper designs a fault-tolerant adaptive controller for air-breathing hypersonic vehicles (AHVs) subject to modelling parameter uncertainties, external disturbances, and actuator nonlinearities of saturation and backlash. The proposed adaptive control scheme is able to compensate the effects of actuator saturation by utilising the states of five auxiliary dynamic systems, which are driven by the differences between the nominal and saturated input signals. Additionally, the effects of control surfaces on the aerodynamic force and moment, which are commonly neglected by the existing adaptive control designs, can be well handled. Transient tracking performance is explicitly derived in terms of norms of the tracking errors. The final control scheme is obtained in a direct form, which makes its implementation more practical compared with other adaptive controllers for AHVs. The effectiveness of the proposed control scheme is demonstrated by numerical simulations. [ABSTRACT FROM AUTHOR]

This paper addresses the finite-time path following control problem for an under-actuated stratospheric airship with input saturation, error constraint, and external disturbances. To handle the adverse effect of input saturation, anti-windup compensators are employed and finite-time convergence of the saturated control solution is established. Error constraints of airship position and attitude are handled by incorporating a tan-type barrier Lyapunov function (TBLF) in guidance and attitude control schemes. Backstepping design is presented with the anti-windup compensators, the TBLF, and nonlinear disturbance observers which estimate the external disturbances. Stability analysis shows that the tracking errors of the airship position converge into a small set around zero within finite-time, the constrained requirements on the airship position and attitude are not violated during operation, and all closed-loop signals are guaranteed to be uniformly ultimately bounded. Compared with the conventional control scheme, simulation results illustrate that the proposed finite-time controller offers a faster convergence rate and a higher path following accuracy for the stratospheric airship. [ABSTRACT FROM AUTHOR]

This paper is concerned with the problem of adaptive output feedback quantised tracking control for a class of stochastic nonstrict-feedback nonlinear systems with asymmetric input saturation. Especially, both input and output signals are quantised by two sector-bounded quantisers. In order to solve the technical difficulties originating from asymmetric saturation nonlinearities and sector-bounded quantisation errors, some special technique, approximation-based methods and Gaussian error function-based continuous differentiable model are exploited. Meanwhile, an observer including the quantised input and output signals is designed to estimate the states. Then, a novel output feedback adaptive quantised control scheme is proposed to ensure that all signals in the closed-loop system are 4-moment (2-moment) semi-globally uniformly ultimately bounded while the output signal follows a desired reference signal. Finally, the effectiveness and applicability of the design methodology is illustrated with two simulation examples. [ABSTRACT FROM AUTHOR]

This paper investigates the leader-following fixed-time output feedback consensus problem for second-order multi-agent systems with input saturation. By combing fixed-time control technique and bi-limit homogeneous systems theory, a class of bounded fixed-time consensus protocols are developed for leader-following multi-agent systems. The protocol design is divided into two parts. First, when all the state information of the followers are measurable, a state feedback consensus protocol is designed to achieve fixed-time consensus. Then, when the velocity information is unmeasurable, an observer-based fixed-time consensus protocol is proposed. With the help of Lyapunov stability theorem and the property of a homogeneous function, it is theoretically shown that the states of all followers can track that of the leader in fixed-time in the presence of input saturation. Finally, numerical simulation is carried out to illustrate the effectiveness of theoretical results. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of robust controller design for a class of discrete-time switching systems with input saturation. To this aim, the composite nonlinear feedback method is extended to design a robust controller with improved performances in terms of the response speed and overshoot in the presence of disturbances and input saturation. The proposed approach is theoretically analysed and its closed-loop stability is proved. Then, the performance of the proposed method is verified using numerical simulations. [ABSTRACT FROM AUTHOR]

In presence of input saturation, a novel integrated guidance and control (IGC) law based on the backstepping technique is proposed for missiles attacking manoeuvring target in this paper. A modified saturation function and an auxiliary system are proposed to deal with the input saturation. The state of the auxiliary system is used in the IGC law design process and stability analysis. Considering the uncertainties caused by target manoeuvres, model errors and variation of the aerodynamic parameters, disturbance observers which converge in finite time are introduced to estimate and compensate them. Based on the Lyapunov theory, the detailed stability analysis of the closedloop system is presented. The non-linear numerical simulations are presented to illustrate the effectiveness of the proposed IGC law. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem of adaptive bounded control for the trajectory tracking of a Quadrotor Aerial Vehicle (QAV) while the input saturations and uncertain parameters with the known bounds are simultaneously taken into account. First, to deal with the underactuated property of the QAV model, we decouple and construct the QAV model as a cascaded structure which consists of two fully actuated subsystems. Second, to handle the input constraints and uncertain parameters, we use a combination of the smooth saturation function and smooth projection operator in the control design. Third, to ensure the stability of the overall system of the QAV, we develop the technique for the cascaded system in the presence of both the input constraints and uncertain parameters. Finally, the region of stability of the closed-loop system is constructed explicitly, and our design ensures the asymptotic convergence of the tracking errors to the origin. The simulation results are provided to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive prescribed performance output-feedback control scheme is proposed for a class of switched nonlinear systems with input saturation. The MT-filters are employed to estimate the unmeasured states and the unknown functions are approximated by the radial basis function neural networks in controller design procedure. It is proved that all the signals in the closed-loop system are semi-globally uniformly ultimately bounded and the tracking error satisfies the prescribed performance. Finally, simulation results are given to illustrate the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]

The regional robust stabilisation by means of linear time-invariant state feedback control for a class of uncertain MIMO nonlinear systems with parametric uncertainties and control input saturation is investigated. The nonlinear systems are described in a differential algebraic representation and the regional stability is handled considering the largest ellipsoidal domain-of-attraction (DOA) inside a given polytopic region in the state space. A novel set of sufficient Linear Matrix Inequality (LMI) conditions with new auxiliary decision variables are developed aiming to design less conservative linear state feedback controllers with corresponding larger DOAs, by considering the polytopic description of the saturated inputs. A few examples are presented showing favourable comparisons with recently published similar control design methodologies. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of finite-time stabilisation by output feedback for a class of non-holonomic systems in chained form with input saturation. Rigorous design procedure for saturated output feedback control is presented by using the homogeneous domination approach and the nested saturation technique. Together with a novel switching control strategy, the designed controller renders that the states of closed-loop system are regulated to zero in a finite time. A simulation example is provided to illustrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper considers the problem of global finite-time stabilisation by output feedback for a class of feedforward (upper triangular) nonlinear systems with input saturation. Based on the finite-time stability theorem, and by skillfully using the homogeneous domination approach and the nested saturation technique, a saturated output feedback controller is successfully constructed, which renders the origin of the closed-loop system globally finite-time stable. In simulation studies, a numerical example is illustrated to show the effectiveness of the control scheme. Moreover, the design strategy is successfully applied to solve the saturated finite-time control problem for vertical wheel on rotating table. [ABSTRACT FROM AUTHOR]

In this study, we consider a boundary control problem of a flexible aerial refuelling hose in the presence of input saturation. To provide an accurate and concise representation of the hose's behaviour, the flexible hose is modelled as a distributed parameter system described by partial differential equations (PDEs). By using the backstepping method, a boundary control scheme is proposed based on the original PDEs to regulate the hose's vibration. An auxiliary system based on a smooth hyperbolic function and a Nussbaum function is designed to handle the effect of the input saturation. Then based on Lyapunov's direct method, the state of the system is proven to converge to a small neighbourhood of zero by appropriately choosing design parameters. Finally, the results are illustrated using numerical simulations for control performance verification. [ABSTRACT FROM AUTHOR]

In this study, we consider the boundary control problem of a flexible manipulator in the presence of input saturation and input disturbances. The dynamics of the flexible system are represented by partial differential equations (PDEs). Based on disturbance observers, a boundary control scheme is designed to regulate angular position and suppress elastic vibration simultaneously. The proposed control scheme allows the application of smooth hyperbolic functions, which satisfy physical conditions and input restrictions, easily be realised. It is proved that the proposed control scheme can be guaranteed in handling input saturation and external disturbances. The stability is achieved through rigorous analysis without any simplification of the dynamics. Numerical simulations demonstrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Considering interconnections among subsystems, we propose an adaptive neural tracking control scheme for a class of multiple-input-multiple-output (MIMO) non-affine pure-feedback time-delay nonlinear systems with input saturation. Neural networks (NNs) are employed to approximate unknown functions in the design procedure, and the separation technology is introduced here to tackle the problem induced from unknown time-delay items. The adaptive neural tracking control scheme is constructed by combining Lyapunov–Krasovskii functionals, NNs, the auxiliary system, the implicit function theory and the mean value theorem along with the dynamic surface control technique. Also, it is proven that the strategy guarantees tracking errors converge to a small neighbourhood around the origin by appropriate choice of design parameters and all signals in the closed-loop system uniformly ultimately bounded. Numerical simulation results are presented to demonstrate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper studies decentralised neural adaptive control of a class of interconnected nonlinear systems, each subsystem is in the presence of input saturation and external disturbance and has independent system order. Using a novel truncated adaptation design, dynamic surface control technique and minimal-learning-parameters algorithm, the proposed method circumvents the problems of ‘explosion of complexity’ and ‘dimension curse’ that exist in the traditional backstepping design. Comparing to the methodology that neural weights are online updated in the controllers, only one scalar needs to be updated in the controllers of each subsystem when dealing with unknown systematic dynamics. Radial basis function neural networks (NNs) are used in the online approximation of unknown systematic dynamics. It is proved using Lyapunov stability theory that all the signals in the closed-loop system are semi-globally uniformly ultimately bounded. The tracking errors of each subsystems, the amplitude of NN approximation residuals and external disturbances can be attenuated to arbitrarily small by tuning proper design parameters. Simulation results are given to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]