A study on hypersonic vehicle (HSV) with centroid shift and actuator fault is made to investigate the adaptive fault-tolerant control for stability recovery of HSV operating in off-nominal conditions. Based on the modelling and analyzing the influence of centroid shift and actuator fault on HSV, the centroid shift can cause system uncertainty, variation of inertial matrix, eccentric moment and strong coupling between the longitudinal and lateral motions, resulting in the high demand for controller. According to the difference of response time, the attitude system of HSV is divided into slow and fast loop. For handling the effect of centroid shift, actuator fault and external disturbance, an improved sliding mode controller combined with adaptive estimator is designed for the slow-loop. Nonlinear general predictive controller (NGPC) assisted by adaptive radial basis function neural network (RBFNN) is developed for fast-loop. In addition, the nonsingular improvements to fast-loop controller are also made to cope with such the problem caused by the estimation of inertial matrix. The stability and tracking ability of the system are analyzed by the Lyapunov theorem of stability. At last, the simulation results show that the fault-tolerant control algorithm provided in this paper is very effective.

Compared with the classical Lyapunov asymptotic stability, finite-time stability is much more important and significant in some practical applications. The purpose of this study is to design the distributed controllers such that the controlled spatially interconnected systems are well-posed, finite-time stable/bounded and finite-time contractive. First, the authors introduce the definitions of finite-time stability/boundedness and finite-time contractiveness for spatially interconnected systems based on the given system matrices. Second, a sufficient condition is proposed to check the well-posedness, finite-time stability/bounedness and finite-time contractiveness of spatially interconnected systems. Third, the distributed controllers are designed to solve the distributed finite-time control problem. Besides, the existence condition and construction of the distributed controllers are shown. In the end, a one-dimensional heat equation example is demonstrated to verify the effectiveness of the proposed control method.

This study focuses on the fault detection for a switched system with all subsystems unstable. Firstly, to eliminate the instability brought by unstable modes, the average dwell time method is introduced to generate the time-driven switching signal. Under the effect of the signal, the exponential stability is guaranteed. Afterwards, the authors utilise the Luenberger observer as the fault detector. Considering the unobservable conditions (A, C), this study gives the new solution to the observer design. Taking the disturbance robustness and fault sensitivity into account, they borrow the mixed performance index from the existing researches. Sufficient conditions are supplied to ensure the system is exponentially stable with mixed performance using linear matrix inequalities. Finally, examples are provided to prove the validity and effectiveness of the proposed switching method and designed fault detector.

This study is concerned with the estimation problem for systems with both missing inputs and measurements but without any acknowledgement mechanism. The acknowledgement mechanism is used to provide the estimator with the status information that whether the input is lost or not during the transmission. Affected by the missing input with unknown status information, the probability density function of system state is a Gaussian mixture, of which the number of terms is growing exponentially with time. Two major limitations of state estimation for these systems are (i) the computational inefficiency of the optimal estimation and (ii) the undetermined stability of the approximate optimal estimation. Thus, the aim of this study is to design an estimator such that it can enhance computational efficiency greatly while its stability can be guaranteed simultaneously. Using Kullback–Leiber divergence, an approximate optimal estimator, which is named as the KLD estimator, is developed as an efficient alternative to the optimal one. By establishing a Riccati-like equation subject to both-side packet dropouts, a sufficient and necessary condition is given for the stability of the KLD estimator. It reveals an interesting fact that the proposed approximate optimal estimator has the same stability as the optimal estimator.

The work is interested in the extended dissipative filtering issue for switched singular discrete-time systems with sensor failures. The persistent dwell-time switching regularity is utilised to describe the successive occurrence of slow switching and fast switching in a switched singular system. A set of variables, which take values in a fixed interval, are utilised for the quantitative analysis of the sensor failures. The main objective is centred on designing a reliable mode-dependent filter which can ensure that the resulting filtering error system is exponentially admissible and simultaneously satisfies the extended dissipative property in the presence of sensor failures. By adopting suitable decoupling methods and introducing reasonable matrix transformation techniques, some relaxed sufficient conditions are derived. The filter gains can be obtained by solving a convex optimisation problem in terms of linear matrix inequalities. Finally, an illustrative example is presented to verify the applicability of the designed filter.

Motivated by Markovian regime-switching diffusion (MRSD), time-varying delays and non-linear coupling forms, this study is concerned with stabilisation of coupled regime-switching diffusion with time-varying delays (CRSDTD) under periodically intermittent control. Compared with most papers investigating MRSD, a striking feature of regime-switching diffusion is that in the two-component process , switching process depends on the diffusion , which can be regarded as the x-dependent process briefly. It is worth mentioning that time-varying delays and non-linear coupling forms are taken into consideration when modelling, which makes their work more realistic. Moreover, a periodically intermittent controller is adopted to guarantee that CRSDTD can achieve the pth moment exponential stability and some sufficient conditions are derived by using the Lyapunov method and Kirchhoff's matrix tree theorem. Furthermore, to illustrate the applicability of their theoretical results, an application to regime-switching coupled oscillators with time-varying delays (RSCOTD) is presented and a stability criterion is given. Conclusively, numerical simulations on RSCOTD are presented to illustrate the effectiveness of the theoretical results.

The present study mainly focuses on designing a stochastic sampled-data controller for chaotic Takagi–Sugeno (T–S) fuzzy systems. Distinct to the existing controller schemes, in this work, the random time delay is introduced into the proposed control scheme that ensures the exponential stabilisation of T–S fuzzy models. In addition, the input delays are assumed to be randomly time-varying, which copes with the traditional uncorrelated Bernoulli distributed sequences. Based on the proposed Lyapunov–Krasovskii functional and using new weighted integral inequalities, the stability and stabilisation conditions are derived and expressed in terms of linear matrix inequalities, which ensure the exponential stability of the states. Finally, in the simulation results, the chaotic nature of two dynamical systems are considered for validation of the derived conditions. From the simulation results, it is concluded that the proposed method can provide better stability performance and less conservative results.

An optimal control problem for backward doubly stochastic system is considered, where the control domain is not necessarily convex. By the method of classical spike variation and duality technique, one necessary condition and one sufficient condition are established for this kind of optimal control problem. The related adjoint process is characterised by the solution of a forward doubly stochastic differential equation, which formulates a forward–backward doubly stochastic differential equation coupled with the state equation. As an illustration, the authors' theoretical results are applied to study an optimal harvesting problem and a linear-quadratic optimal control problem. Moreover, the corresponding maximum principle with an initial state constraint is obtained by Ekeland's variational principle.

This study addresses the positive filter design problem for continuous-time positive Markov jump linear systems (PMJLSs). Based on the necessary and sufficient condition for -gain performance, two sufficient conditions to design positive full-order and reduced-order -filters for PMJLSs are provided in terms of linear programming, respectively. A practical numerical example of an isotropic, homogeneous and unidimensional aquifer is presented at last to show the effectiveness of the proposed schemes.

This study presents a switched system approach to distributed guaranteed cost control for a class of interconnected systems, where the subsystems of the interconnected system are coupled via states. In the proposed scheme, the subsystems communicate with each other through a network with communication losses caused by the communication constraint or network attacks. The communication-based interconnected system is modelled as a switched system with parameters uncertainties in system matrixes induced by sampling jitter and network time-varying delays. The stability analysis and guaranteed cost controller design are presented by applying the average dwell time method. Meanwhile, a quantitative relation between the system performance and the communication quality is established. Finally, numerical simulations are given to show the effectiveness of the proposed results.

This study proposes a novel kind of unknown input observer (UIO) called reset unknown input observer (R-UIO) for state estimation of linear time invariant (LTI) systems in the presence of disturbance using linear matrix inequality techniques. In R-UIO, the states of the observer are reset to the after-reset value based on an appropriate reset law in order to decrease the norm and settling time of estimation error. It is shown that the application of reset theory to the UIOs in the LTI systems can significantly improve the transient response of the observer. Moreover, the devised approach can be applied to both SISO and MIMO systems. Furthermore, the stability and convergence analysis of the devised R-UIO is addressed. Finally, the efficiency of the proposed method is demonstrated by simulation results.

Switched asynchronous sequential machines (ASMs) are endowed with inherent fault-tolerance capability. This study presents model matching and fault-tolerant control of switched ASMs based on corrective control theory. The objective is to design a corrective controller that matches the stable-state behaviour of the closed-loop system to that of a reference model while overcoming all transient faults infiltrating into the machine. In particular, the proposed control scheme can invalidate not only transient faults causing unauthorised state transitions in single submachine, but also those ones invoking unwanted switching operations between submachines. The existence condition and design procedure for a fault-tolerant corrective controller is addressed in the framework of corrective control. For experimental verification, the proposed scheme is applied to the read-only memory controller for on-board computers implemented on a field programmable gate array system.

In this study, a disturbance observer-based integral fuzzy sliding-mode control methodology for a wind turbine system with a non-linear permanent magnet synchronous generator (PMSG) is proposed using the Takagi–Sugeno fuzzy model. To reduce the hardware cost of the fuzzy controller membership function, an imperfect premise matching condition is considered. Considering the matched disturbance, and an external disturbance acting on the system, a novel integral fuzzy sliding surface is proposed based on a fuzzy disturbance observer (FDOB). Therefore, various forms of external disturbances can be estimated using the FDOB. In addition, a sufficient condition for guaranteeing the asymptotic stability of the sliding motion with performance is proposed using a Lyapunov function and derived using a linear matrix inequality format. Furthermore, a reachability problem of the system states over the proposed sliding surface is derived through an appropriate Lyapunov function. Finally, the simulations for a wind turbine system using a PMSG are implemented to verify the effectiveness of the proposed method as compared with previous studies.

The unscented Kalman filtering problem is investigated for a class of non-linear discrete-time stochastic systems subject to random packet dropout. Here, a random variable, which obeys Bernoulli distribution with known conditional probability, is introduced to depict the phenomenon of packet dropout occurring in a stochastic way. Based on the compensation technology of packet dropout, the one-step prediction value of observer instead of zero-input is used as a compensator when packet dropout occurs. Owing to taking the phenomenon of random packet dropout into account, the authors need to compute parameters to reduce the effects of the compensator. Then, based on the minimum mean square error principle, a new unscented Kalman filtering algorithm is proposed such that, for the random packet dropout, the filtering error is minimised. By solving the recursive matrix equations, the filter gain matrices and error covariance matrices can be obtained and the proposed results can be easily verified by using the standard numerical software. They finally provide two examples, one is a numerical example to show the performance of the proposed approach, and the other is to solve the problem of target estimation for a tracking system with random packet dropout.

This study is concerned with resilient load frequency control (LFC) scheme design of multi-area power systems with communication delay and aperiodic denial-of-service (DoS) attacks. First, to identify DoS attacks, a detection mechanism in the actuator side is proposed which is a time counter measuring the input delay. The identified DoS attacks are constrained by its upper bound of frequency and duration. When DoS attacks are identified, actuator switches to zero-input strategy from hold-input strategy. According to the switching control inputs, switched time delay system model is established to describe the attack influence on LFC system. Further, a criterion of preserving weighted performance is derived by combining piecewise Lyapunov–Krasovskii functional method with switched system method. Based on the criterion, the resilient control gain is designed by solving a set of LMIs. Finally, numerical simulations are given to verify the validness of the attack detection based resilient LFC scheme.

This study addresses the problem of robust fast and high-precision positioning of uncertain one-degree-of-freedom mechanical systems with friction and actuator constraint. The proposed control is constructed within the framework of saturated proportional–derivative (PD) plus relay action. Global asymptotic positioning stability is proven by Lyapunov's direct method with Barbalat's lemma. The appealing features of the proposed control are that it is fairly easy to construct with simple intuitive structure and the absence of modelling parameter in the control law formulation, and thus it is ready to implement for practical applications. An additive feature is that the proposed control embeds the PD action within one saturation function and hence it omits the elaborating embedment of the control gains within the requested constraint. Another feature is that the proposed approach can be explicitly upper bounded a priori and thus, it has the ability to protect the actuator from saturation completely and to ensure global asymptotic stability featuring fast transient and high steady-state positioning. Numerical simulations and real experimental results demonstrate the effectiveness and improved performance of the proposed approach.

This study focuses on the problem of adaptive neural network (NN) tracking control for a class of strict-feedback non-linear switched systems under arbitrary switching. The considered systems are with unknown external disturbances, time-varying delays, and actuator failures. NNs are used to approximate unknown functions and Lyapunov–Karsovskii functionals are utilised to compensate for the time-varying delays. Different from the existing results, piecewise switched adaptive laws are proposed for each subsystem, which can reduce conservativeness caused by using common adaptive laws for all subsystems. Besides, prescribed performance bound (PPB) technique is developed to further improve the transient performance of the systems, especially when actuator failures occur and system switchings take place. Finally, under the framework of Lyapunov theory, an adaptive NN reliable tracking control method is proposed. It is proved that all the signals in the closed-loop system are semi-globally uniformly ultimately bounded and the tracking error remains within the PPBs. A simulation study is given to illustrate the effectiveness of the authors' results.

It is well known that the linear growth condition is an important assumption for the stochastic differential system, which can ensure that the solution of the stochastic system will not explode at a finite time. However, there exist a lot of highly non-linear stochastic differential systems, which do not satisfy the linear growth condition, i.e. their coefficients cannot be bounded by a linear function. In this study, the existence of the unique global solution is first proved for highly non-linear switched stochastic systems with non-random switching signals, where the linear growth condition is not required anymore. In addition, by using the mode-dependent average dwell time approach and the Lyapunov functions method, the pth moment exponential stability is presented for highly non-linear switched stochastic systems with both stable and unstable subsystems. An illustrative example is provided to show the effectiveness of the developed theoretical results.

In this brief, the robust trajectory tracking control problem is addressed for uncertain quadrotor systems with time delays. The quadrotor dynamical model is an under-actuated system subject to non-linearity, unmodelled uncertainties, parametric perturbations, external disturbances, and state and input time delays. A robust cascade trajectory tracking controller is developed by the backstepping method and the robust compensation theory. Theoretical analysis is given to prove that the tracking errors can converge into the given neighbourhood of the origin ultimately. An on-line unidirectional tuning method is given to determine the controller parameters. Experimental results are provided to verify the effectiveness of the proposed control approach and the parameter tuning method.

This brief concerns the set-theoretic recursive state estimation of non-linear systems with polynomial dynamics, making use of ellipsoidal bounds. The sum of squares approach is used to construct an optimal ellipsoid containing the intersection of sets obtained with the use of non-linear system equations and measurement equations. The properties of the proposed filter are illustrated with two examples, one concerning the simultaneous estimation of parameters and state of a linear system, and the other on the Euler equations of the rigid body rotational motion.