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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]

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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]

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]

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, a composite disturbance rejection control method is proposed for attitude control of quadrotor using an inner–outer loop control framework, which can effectively improve the angular tracking performance of the quadrotor and achieve the active disturbance rejection. In the inner loop, a novel nonlinear extended state observer (NESO) is designed to estimate the disturbance and nonlinear part of the system model, then a robust control law is embedded in inner-loop controller to attenuate the effect of the estimation error. In the outer loop, a composite nonlinear feedback (CNF) controller is designed to improve the transient performance. Moreover, the stability of two loops are also analyzed, respectively. Numerical simulation and platform experiment are carried out to verify the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: This article investigates the nonsingular prescribed‐time stabilization problem for p‐normal form systems. Two significant progresses are made for the first time as follows: First, a novel concept named coordinate mapping of time domain, is proposed to transform the nonsingular prescribed‐time convergence problem into the ordinary finite‐time convergence problem of transformed time‐varying system. Second, a set of new parameters are introduced to extend the existing adding a power integrator technique, such that the power restriction is removed. Based on above design procedure, a periodic controller is constructed to stabilize the state of the p‐normal form system into a small neighborhood of the equilibrium in prescribed time. Theoretical result is supported by numerical simulation. [ABSTRACT FROM AUTHOR]

In a nonlinear teleoperation system controlled for task-space position tracking, while the time-varying delay in the communication channel has been addressed, the actuator saturation has not been taken into account yet. Considering that in practice, the actuator saturation is a serious constraint, disregarding it in the controller design stage can cause problems. In this paper, we have proposed a control framework to ensure end-effectors position tracking while satisfying sub-task control in the presence of the nonlinear dynamics for the telemanipulators, bounded time-varying delays in the communication channels and saturation in the actuators. We have shown that in free motion and when the operator applies a bounded force to the local robot, the proposed controller not only guarantees the position convergence of the end-effectors but also guarantees the accomplishment of the sub-task control. The efficiency of the proposed control algorithm is validated showing a number of numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, a robust state-constrained control algorithm is proposed by introducing time-varying barrier Lyapunov functions (BLF) for nonlinear systems with uncertainties. Novel time-varying symmetric/asymmetric forms of error barrier functions are investigated in order to relax the requirements of the initial state compared with existing BLF-based literatures. By integrating the proposed time-varying BLF method with the backstepping technique, constraint satisfaction is achieved and signals in closed-loop are uniform asymptotically stable. In addition, the extended state observer technique is utilized to prevent the constraint violation during the transient phase and strengthen the robustness of the control system in the presence of uncertainties. Numerical simulations are implemented to illustrate the attitude tracking performance obtained from the proposed method for a homing missile with angle of attack constraint, parametric uncertainties and external disturbances. [ABSTRACT FROM AUTHOR]

In this paper, we propose a robust nonlinear control design concept based on a coefficient diagram method and backstepping control, combined with a nonlinear observer for the magnetic levitation system to achieve precise position control in the existence of external disturbance, parameters mismatch with considerable variations and sensor noise in the case, where the full system states are supposed to be unavailable. The observer converges exponentially and leads to good estimate as well as a good track of the steel ball position with the reference trajectory. A simulation results are provided to show the excellent performance of the designed controller. [ABSTRACT FROM AUTHOR]

In this paper, we propose two adaptive control schemes to solve the output tracking control problem of a class of uncertain switched nonlinear systems. The first is a robust scheme constructed based on common Lyapunov function method, aiming to achieve the insensitivity of closed-loop system to parameter switches by estimating the bound on switching parameters. It is analyzed that the system stability under arbitrary switching is established with such a scheme, but the control input required may be relatively large since the estimate of the bound on switching parameters is utilized. To avoid this, we further propose a direct adaptive control scheme by estimating the switching parameters directly, and derive a dwell-time condition for parameter switches based on an extended multiple Lyapunov functions method newly developed, such that the global boundedness of all the closed-loop signals and the convergence of tracking error to a residual around zero are ensured. The effectiveness of the proposed control schemes is illustrated through simulation studies. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the problem of formation control is considered for a class of unknown nonaffine nonlinear multiagent systems under a repeatable operation environment. To achieve the formation objective, the unknown nonlinear agent's dynamic is first transformed into a compact form dynamic linearization model along the iteration axis. Then, a distributed model‐free adaptive iterative learning control scheme is designed to ensure that all agents can keep their desired deviations from the reference trajectory over the whole time interval. The main results are given for the multiagent systems with fixed communication topologies and the extension to the switching topologies case is also discussed. The feature of this design is that formation control can be solved only depending on the input/output data of each agent. An example is given to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Sliding mode control is an efficient and robust control method widely used in nonlinear systems. Power systems are one of the largest nonlinear dynamic systems which their transient stability analyses have a lot of importance. In this paper, sliding mode control is applied for improving the low frequency oscillations damping of a single machine connected to an infinite bus. The performance of the system is analyzed in normal mode operation, post-fault state, after operation of relays (and opening the breakers in the both ends of the faulty line), and reclosing mechanism which returns the line to service. Here, TCSC is employed as an oscillation damper. TCSC can be considered as a controllable impedance determined by the sliding mode control. In addition, a dynamical observer is proposed for the sliding mode controller. Simulation results demonstrate that, the performance of the power system in damping the low frequency oscillations is improved significantly. [ABSTRACT FROM AUTHOR]

In this paper, we apply the active disturbance rejection control approach to output-feedback stabilization for uncertain lower triangular nonlinear systems with stochastic inverse dynamics and stochastic disturbance. We first design an extended state observer (ESO) to estimate both unmeasured states and stochastic total disturbance that includes unknown system dynamics, unknown stochastic inverse dynamics, external stochastic disturbance, and uncertainty caused by the deviation of control parameter from its nominal value. The stochastic total disturbance is then compensated in the feedback loop. The constant gain and the time-varying gain are used in ESO design separately. The mean square practical stability for the closed-loop system with constant gain ESO and the mean square asymptotic stability with time-varying gain ESO are developed, respectively. Some numerical simulations are presented to demonstrate the effectiveness of the proposed output-feedback control scheme. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A generalized homogeneous exact set-point tracking control methodology for a class of disturbed higher-order nonlinear systems is investigated in this paper. By virtue of utilizing the disturbance estimation and active elimination approach, a homogeneous domination feedback technique is then integrated such that a generalized composite active anti-disturbance control framework is proposed with a delicate handling procedure of the non-vanishing nonlinearities. The proposed methodology has several new features. First, a genuine nonlinear composite controller employing the system nonlinearities will bring an improvement of the control performances. Second, the flexility of the design methodology renders its suitability for random output tracking with mismatched disturbances in every channel. Moreover, the control function is constructed in a neat nested form and hence easier to be implemented. Numerical simulation results affirm the output tracking control performances. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Most of existing results on robust output regulation problem of singular nonlinear systems are limited to local solutions. In this paper, the semi-global robust output regulation problem for a class of singular nonlinear systems is investigated by using a nonlinear internal model. Attaching a nonlinear internal model to the singular nonlinear system yields an augmented singular nonlinear system whose semi-global robust stabilisation solution leads to the solution of the semi-global robust output regulation problem of the original singular nonlinear system. The solvability conditions of the semi-global output regulation problem are established by addressing the solvability of the robust stabilisation problem of augmented singular nonlinear system. Finally, a numerical simulation example is used to illustrate the design of the semi-global regulator for the singular nonlinear systems. [ABSTRACT FROM AUTHOR]

This paper proposes a tracking control strategy for nonlinear systems without needing a prior knowledge of the reference trajectory. The proposed method consists of a set of local controllers with appropriate overlaps in their stability regions and an on-line switching strategy which implements these controllers and uses some augmented intermediate controllers to ensure steering the system states to the desired set points without needing to redesign the controller for each value of set point changes. The proposed approach provides smooth transient responses despite switching among the local controllers. It should be mentioned that the stability regions of the proposed controllers could be estimated off-line for a range of set-point changes. The efficiencies of the proposed algorithm are illustrated via two example simulations. [ABSTRACT FROM AUTHOR]

In the present work, we propose a supervised multimodel repetitive–predictive control scheme for discrete-time nonlinear systems in order to reject unknown non-stationary sinusoidal disturbances and to track reference trajectory. The nonlinear system is described by the decoupled state multimodel. Also, a non-stationary sinusoidal unknown input multi-observer is used to estimate the state and the unknown non-stationary sinusoidal disturbances simultaneously. The estimate of the disturbances is exploited by the magnitude–phase-locked loop (MPLL) approach to reconstruct the accurate disturbance period used to develop a robust supervised multi-rejector. The proposed control strategy provides good closed-loop performance despite the changes of the disturbance characteristics. A simulation example is provided to illustrate the significance of the proposed multi-rejector. [ABSTRACT FROM AUTHOR]

In this paper, a novel predictive smooth variable structure filter (PSVSF) is presented for attitude synchronization during satellite formation flying (SFF). The strategy is proposed based on variable structure control concept and applies to any nonlinear system with modeling errors. Because the modeling errors in the PSVSF are not restricted to Gaussian noise only, the technique can deal with various kinds of uncertainties, parameter variations, or noises. It also has low computational burden; therefore, it is more general than other nonlinear estimation methods. Sufficient conditions to analyze the stability and characteristics of the PSVSF are presented. Simulations are performed to demonstrate the accuracy, robustness, and stability of the proposed PSVSF for the attitude synchronization estimation of the SFF system. [ABSTRACT FROM PUBLISHER]

This paper presents the mathematical modeling of a multivariable process used in level control, under the assumptions that all pipes are filled with fluid and the inertial effects caused by flow variations, in case of small accelerations, are neglected. Because of the way the two tanks are interconnected and interact with each other, the resulting mathematical model is nonlinear. In the paper it is proposed a robust control algorithm for this plant developed based on H-infinity loop shaping procedure. The required computations and the study of the behavior of the system are done in the Matlab simulation environment. [ABSTRACT FROM AUTHOR]

Dual-winding bearingless switched reluctance motor (BSRM) is a multivariable high-nonlinear system characterized by strong coupling, and it is not completely reversible. In this paper, a new decoupling control strategy based on improved inverse system method is proposed. Robust servo regulator is adopted for the decoupled plants to guarantee control performances and robustness. A phase dynamic compensation filter is also designed to improve system stability at high-speed. In order to explain the advantages of the proposed method, traditional methods are compared. The tracking and decoupling characteristics as well as disturbance rejection and robustness are deeply analyzed. Simulation and experiments results show that the decoupling control of dual-winding BSRM in both reversible and irreversible domains can be successfully resolved with the improved inverse system method. The stability and robustness problems induced by inverse controller can be effectively solved by introducing robust servo regulator and dynamic compensation filter. [ABSTRACT FROM AUTHOR]

Event-triggering strategy is one of the real-time control implementation techniques which aims at achieving minimum resource utilisation while ensuring the satisfactory performance of the closed-loop system. In this paper, we address the problem of robust stabilisation for a class of nonlinear systems subject to external disturbances using sliding mode control (SMC) by event-triggering scheme. An event-triggering scheme is developed for SMC to ensure the sliding trajectory remains confined in the vicinity of sliding manifold. The event-triggered SMC brings the sliding mode in the system and thus the steady-state trajectories of the system also remain bounded within a predesigned region in the presence of disturbances. The design of event parameters is also given considering the practical constraints on control execution. We show that the next triggering instant is larger than its immediate past triggering instant by a given positive constant. The analysis is also presented with taking delay into account in the control updates. An upper bound for delay is calculated to ensure stability of the system. It is shown that with delay steady-state bound of the system is increased than that of the case without delay. However, the system trajectories remain bounded in the case of delay, so stability is ensured. The performance of this event-triggered SMC is demonstrated through a numerical simulation. [ABSTRACT FROM AUTHOR]

In this paper, we consider the control problem for a general class of nonlinear system subjected to uncertain dynamics and non-varnishing disturbances. A smooth nonlinear control algorithm is presented to tackle these uncertainties and disturbances. The proposed control design employs the integral of a nonlinear sigmoid function to compensate the uncertain dynamics, and achieve a uniformly semi-global practical asymptotic stable tracking control of the system outputs. A novel Lyapunov-based stability analysis is employed to prove the convergence of the tracking errors and the stability of the closed-loop system. Numerical simulation results on a two-link robot manipulator are presented to illustrate the performance of the proposed control algorithm comparing with the layer-boundary sliding mode controller and the robust of integration of sign of error control design. Furthermore, real-time experiment results for the attitude control of a quadrotor helicopter are also included to confirm the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Robust fault estimation plays an important role in real-time monitoring, diagnosis, and fault-tolerance control. Accordingly, this paper aims to develop an effective fault estimation technique to simultaneously estimate the system states and the concerned faults, while minimizing the influences from process/sensor disturbances. Specifically, an augmented system is constructed by forming an augmented state vector composed of the system states and the concerned faults. Next, an unknown input observer (UIO) is designed for the augmented system by decoupling the partial disturbances and attenuating the disturbances that cannot be decoupled, leading to a simultaneous estimate of the system states and the concerned faults. In order to be close to the practical engineering situations, the process disturbances in this study are assumed not to be completely decoupled. In the first part of this paper, the existence condition of such an UIO is proposed to facilitate the fault estimation for linear systems subjected to process disturbances. In the second part, robust fault estimation techniques are addressed for Lipschitz nonlinear systems subjected to both process and sensor disturbances. The proposed technique is finally illustrated by the simulation studies of a three-shaft gas turbine engine and a single-link flexible joint robot. [ABSTRACT FROM AUTHOR]

Interval type-2 fuzzy logic controller (IT2FLC) method for controlling the speed with a direct stator flux orientation control of doubly fed induction motor (DFIM) is proposed. The fuzzy controllers have demonstrated their effectiveness in the control of nonlinear systems, and in many cases it is proved that their robustness and performance are less sensitive to parameters variation over conventional controllers. The synthesis of stabilizing control laws design based on IT2FLC is developed. A comparative analysis between type-1 fuzzy logic controller (T1FLC) and IT2FLC of the DFIM is shown. Simulation results show the feasibility and the effectiveness of the suggested method to the control of the DFIM under different operating conditions such as load torque and in the presence of parameters variation. [ABSTRACT FROM AUTHOR]

This paper studies the fixed-time composite robust tracking control problem of a class of marine surface vessel (MSV) systems with uncertainty items and external disturbances. First, the tracking error is restricted within the bounded range by the tan-type barrier Lyapunov function (TT-BLF). Second, a fixed-time disturbance observer (FTDO) is designed to offset the lumped disturbances caused by system uncertainty items and external disturbances. Then, relying on the characteristics of H ∞ control, the error is limited within the L 2 norm bounded by suppressing the interference of the observation error. Furthermore, considering the importance of saving network resources, an event-triggered controller based on relative thresholds is proposed, which guarantees excellent robustness while greatly reducing the communication bandwidth. Finally, it is shown by Lyapunov stability analysis that all error signals of the nonlinear system converge to a small region close to zero in fixed time under the guidance of the robust control law. The effectiveness of the proposed composite robust controller is verified by numerical simulation results. • A fixed-time observer is employed to offset the lumped disturbances caused by system uncertainty items and external disturbances. • An H∞ control strategy is proposed to improve robustness, which has L 2 gain less than or equal to given γ. • A composite robust controller is proposed to ensure the error signal converge to a small range near zero within a predetermined time and robustness. • A ETS based on relative threshold is developed to greatly reduce the communication bandwidth of the controller. [ABSTRACT FROM AUTHOR]

Integrated guidance and control of an elastic flight vehicle based on constrained robust model predictive control is proposed. The design is based on a partial state feedback control law that minimizes a cost function within the framework of linear matrix inequalities. It is shown that the solution of the defined optimization problem stabilizes the nonlinear plant. Nonlinear kinematics and dynamics are taken into account, and internal stability of the closed-loop nonlinear system is guaranteed. The performance and effectiveness of the proposed integrated guidance and control against non-maneuvering and weaving targets are evaluated using computer simulations. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a robust controller for four wheel independently-actuated (FWIA) electric ground vehicles to preserve vehicle stability and improve vehicle handling performance. Thanks to the actuation flexibility of FWIA electric ground vehicles, an external yaw moment, which is usually employed to regulate the vehicle yaw and lateral motions, can be easily generated with the torque differences between the left and right side motors. A μ-synthesis control method which can deal with unmodeled dynamics and parametric uncertainties is proposed by taking the external yaw moment as the control input. Simulations with a high-fidelity, CarSim®, full-vehicle model are carried out to demonstrate the effectiveness of the proposed control system. Simulation results in various driving scenarios with vehicle payload variations show the robustness of the proposed controller.w [ABSTRACT FROM AUTHOR]

This paper proposes new techniques to calculate the dynamic gains of nonlinear systems represented by fuzzy basis function network (FBFN) models. The dynamic gain of an FBFN can be approximated by finding the maximum of norm values of the locally linearized systems or by solving a non-smooth optimal control problem. From the proposed gain calculation techniques, a novel adaptive multilevel fuzzy controller (AMLFC) with a maximum output scaling factor is presented. To guarantee the system stability, a stability condition is derived, which only requires that the output scaling factor of the AMLFC be bounded. Therefore, this paper provides a systematic and simple design practice for controlling nonlinear systems by using an AMLFC. The AMLFC is simulated in a tower crane control system. Simulation results show that AMLFC is not only robust but also provides improved transient performances compared with the robust adaptive fuzzy controller. [ABSTRACT FROM AUTHOR]

The attitude control of a launch vehicle is a challenging task due to the dramatically varying vehicle dynamics along a flight path. The objective of this paper is to design a switching robust control strategy for launch vehicles, applied here to a notional nanosat launch vehicle. In order to control the rocket along a trajectory ascending through the Earth's atmosphere, a set of operating points at different times along the flight path are selected, the corresponding dynamics models of the rocket are obtained via linearization, and a robust H ∞ controller is designed for each operating point using the linear matrix inequality approach. These controllers are applied to the nonlinear plant model via a switching strategy when the rocket flies along the flight path. Both linear and nonlinear simulation results are given to show the performance of the closed-loop system. [ABSTRACT FROM AUTHOR]

A continuous stirred tank reactor (CSTR) is a typical example of chemical industrial equipment, whose dynamics represent an extensive class of second order nonlinear systems. It has been witnessed that designing a good control algorithm for the CSTR is very challenging due to the high complexity. The two difficult issues in CSTR control are state estimation and external disturbance attenuation. In general, in industrial process control a fast and robust response is essential. Driven by these challenging issues and desired performance, this paper proposes an output feedback terminal sliding mode control (TSMC) framework which is developed for CSTR, and can estimate the system states and stabilize the system output tracking error to zero in a finite time. The corresponding stability analysis is presented in terms of the Lyapunov method. Illustrative examples are demonstrated by using Matlab simulations to validate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

The disturbance-observer-based control (DOBC) is a well-known robust control scheme and recently its non-linear version has been developed. Observing that two components (so-called Q-filters) in the conventional DOBC structure have the same transfer function, the authors propose a reduced-order DOBC for uncertain non-linear systems. It is shown that the proposed controller also guarantees the same robust transient response as those developed before. Numerical simulations using a magnetic levitation system are included to illustrate the detailed design procedure and validate the performance of the proposed controller. [ABSTRACT FROM AUTHOR]

• Compared with design methods in related results, the novel piecewise constant virtual control signals are designed and the requirement of designing a differentiator is avoided. Thus, the backstepping method in this paper is more suitable for networked control systems. • A semi-synchronous event-triggered scheme is designed. Compared with some conventional event-triggered schemes, the triggering instants among the channels are largely staggered to reduce network congestion; A self-triggered scheme is further proposed to avoid the continuous monitoring of the event-triggered conditions. • Compared with some switching methods, the constraints of ADT are canceled to allow more frequent switchings. • A class of nonlinear systems with Hölder condition and linear growth condition is introduced, such that the robustness of the proposed backstepping method is extended. The paper investigates the backstepping robust control problem for a class of nonlinear networked systems. The non-Lipschitz conditions of linear growth condition and Hölder condition are considered in the time-varying disturbance and uncertainty. An important innovation is that the virtual controller is designed to be piecewise constant such that the usage of the command filter is avoided. In the process of designing the robust controller, a semi-synchronous event-triggered scheme is proposed to relieve the communication pressure in high-order systems. Thus, a switched controller without using average dwell time (ADT) is considered. The finite-time practical stability with the form of fast terminal sliding mode (TSM) is also obtained. Then, the Zeno behavior is excluded and a self-triggered scheme is further proposed to avoid the continuous monitoring of the event-triggered conditions. Compared with some existing command-filtered results, the design process is simplified and more suitable for networked systems. The effectiveness of the proposed theory is validated by the numerical simulation of a hypersonic vehicle. [ABSTRACT FROM AUTHOR]

This paper investigates the tracking control problem of multi-input and multi-output nonlinear systems simultaneously considering the user-specified tracking performance, the asymmetric input saturation, and external disturbances. By introducing the modification signals into the user-specified performance functions, we propose a flexible performance-based control scheme, featuring the capability of avoiding the violation of the resulted modified performance functions (MPFs) due to the input saturation. These modification signals are associated with input saturation errors (the errors between the actual and desired control inputs) and generated by a novel auxiliary system in which all the states are guaranteed to be nonnegative. Consequently, the MPF can degrade the user-specified tracking performance when saturation happens and can recover it when no saturation occurs. Furthermore, the disturbance observer is utilized to estimate external disturbances and relieve the burden on the selection of control gains. With the developed control scheme, it is theoretically shown that the output can always track the reference signal and satisfy the constraints of the MPFs. Finally, the numerical simulation results are presented to show the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]