Optimal dropout policies for networked control systems

By realizing the feedback paths over communication networks, we get a class of networked control systems (NCSs), where the network's quality‐of‐service (QoS) is commonly characterized by the average dropout rate of feedback data packets. The control performance of an NCS however, is determined not only by the average dropout rate but also by the dropout pattern of feedback data packets. This paper provides a systematic way to determine the optimal dropout pattern (policy) under a given average dropout rate, where the performance is measured by the output signal power under an exogenous white noise. By modeling the finite‐memory dropout policies with the general Markov chain, this paper formulates the optimal dropout policy design into the optimization of parameters of a dropout Markov chain. That optimization is first solved by an augmented Lagrangian gradient method, which may be stuck at local optima because of the problem's non‐convexity. To compensate this weakness, we apply the branch‐and‐bound method to the optimization whose constraints are bilinear. The branch‐and‐bound method can approach the global optimal solution with any desired tolerance in finite steps. The obtained optimal dropout policy may be interpreted as a network's QoS constraint whose enforcement provides a hard guarantee on the control system's performance. An example is used to illustrate the effectiveness of the achieved results. Copyright © 2012 John Wiley & Sons, Ltd.     

Robust guaranteed cost control of discrete‐time networked control systems

This paper is concerned with the robust guaranteed cost control problem for networked control systems (NCSs). The plant considered is an uncertain linear discrete‐time system, where the communication limitations include packet‐loss and signal transmission delay. Our purpose is to design a robust state‐feedback guaranteed cost controller such that the resulting closed‐loop system is robustly stable, and a specified quadratic cost function is upper bound for all admissible uncertainties under such communication limitations. A model of NCSs is established which contains two additive delay components, one being a known constant, and the other unknown constant. By introducing a novel Lyapunov‐Krasoviskii function with the idea of delay partitioning, new sufficient conditions for the existence of guaranteed cost controllers are proposed. Numerical examples are provided to demonstrate the usefulness of the developed theory. Copyright © 2010 John Wiley & Sons, Ltd.     

Nonfragile reliable control for positive switched systems with actuator faults and saturation

This paper presents a nonfragile reliable control approach to positive switched systems with actuator faults and saturation. In order to guarantee the reliability of the controller, the controller gain matrix is chosen as the sum of a normal gain matrix and a gain perturbation matrix. A nonfragile reliable control is first proposed for the considered systems using a gain matrix decomposition technique. Then, the presented nonfragile control design approach is developed for the systems with exogenous disturbances. An approach to compute the normal gain matrix and the gain perturbation matrix is also provided. Under the obtained controller, the resulting closed‐loop systems are positive and L₁‐gain stable. Meanwhile, all the states will stay inside a cone. All presented conditions are described via linear programming. Finally, two examples are provided to verify the effectiveness of the theory findings.     

Robust fault detection for networked control systems with packet dropouts: An average dwell time method

The problem of fault detection for networked control systems with respect to packet dropouts is investigated in this paper based on average dwell time method. For the cases that there may be sensor stuck failure and packet dropouts, the networked control systems are modeled as discrete time switched systems. Subsequently, a novel fault detection scheme, which is valid to detect the failures with small magnitudes even the outage ones, is proposed by making the generated residuals sensitive to servo inputs in faulty cases and robust against it in normal case. By utilizing the average dwell time method, new sufficient conditions, which include some existing results, for characterizing the sensitivity performance and the attenuation performance are presented in terms of linear matrix inequalities. Meanwhile, the relation between the packet dropout rate and the system performance is established. Finally, an application of a linearized aircraft is given to demonstrate the effectiveness of the proposed results. Copyright © 2014 John Wiley & Sons, Ltd.     

Stochastic control of networked control systems with packet dropout and time‐varying delay

This paper studies the stochastic stabilization problem for discrete‐time networked control systems with time delay and packet dropout. The message losses and time delay from the sensor to the controller and from the controller to the actuator are considered simultaneously. A two‐state Markov chain is used to model the correlated packet dropout process. By introducing free weighting matrices, the sufficient condition on the stochastic stability of such networked control system is obtained. An improved criterion is found by introducing the delay fractioning method and a new Lyapunov–Krasovskii functional. On the basis of the stability condition, the mode‐dependent controller is given in terms of linear matrix inequalities. A simulation example is given to show the proposed results. Copyright © 2012 John Wiley & Sons, Ltd.     

Fault detection for linear stochastic systems with sensor stuck faults

This paperaddresses the fault detection (FD) problem for Itô‐type linear stochastic systems with a class of sensor stuck faults and reference inputs. Considering all the possible sensor stuck faults, the stochastic systems are modeled via multi‐models, i.e. fault‐free model and faulty models. The main contributions are that a novel FD scheme in stochastic setting is proposed that is valid for arbitrary small sensor stuck faults including outage cases (the stuck values are zero). In addition, convex conditions for characterizing fault sensitivity performance and disturbance attenuation performance in stochastic sense are presented and these conditions include some previous results on deterministic systems as a special case. Finally, two examples are used to demonstrate the method and its effectiveness. Copyright © 2011 John Wiley & Sons, Ltd.     

Integrated fault tolerant attitude control approach for satellite attitude system with sensor faults

In this study, a novel integrated fault tolerant control (FTC) strategy is proposed for a rigid satellite attitude systems under the case of external disturbance, Lipschitz nonlinearity, and sensor faults. Different from the traditional adaptive fault estimation method, an augmented fault estimation observer is designed for the considered faulty satellite attitude system, which could be used for estimating both system state and sensor fault. A virtual observer is firstly introduced, and then, a real observer is derived as a result of the unmeasurable information to be used for the design of the virtual observer. On this basis, an integrated FTC approach is developed for the considered faulty satellite attitude system by combining backstepping control and fractional order nonsingular terminal sliding mode control techniques, such that the closed-loop system not only has good robustness to external disturbance but also has better fault tolerance capability to unknown sensor fault. Finally, a simulation example is provided to demonstrate the feasibility and advantage of the proposed FTC scheme.     

The improved H∞ controller design for nonlinear networked control systems with random communication delays

This paper is concerned with the observer‐based H_∞ controller design problem for nonlinear networked control systems with random communication delays. Firstly, the dynamic observer‐based control scheme is modelled, where the control input of the observer is different from the control input of the plant. Then, a less conservative delay‐dependent H_∞ stabilization criterion is derived by using an improved Lyapunov function. And the proof of stabilization criterion is completed in terms of four cases when the time delays in two communication channels are constant or time‐varying, respectively. The derived stabilization criterion is formulated in the form of a non‐convex matrix inequality, which can be solved by an optimal cone complementary linearization iteration algorithm to obtain the minimum disturbance attenuation level. Finally, several numerical examples and an illustrative example are provided to clarify the effectiveness and merits of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamic output feedback of networked control systems with partially known Markov chain packet dropouts

In this paper, a class of networked control systems with output feedback control and H _∞ performance is discussed. It considers packet dropouts in both measurement (S/C) and actuation (C/A) channels. Markovian chain principle is used in modeling the packet dropouts in S/C and C/A channels. The time scale adopted in these two independent homogeneous Markov chain is linear with the physical time. The model also takes into consideration the late arriving packets. The effect of interaction between packet dropouts in both channels on the stability of system, when the networks of both (S/C) and (C/A) channels overlap is also examined. Sufficient condition for the existence of H _∞ output feedback controller is presented and it is shown that it is dependent on the upper bounds of the number of consecutive packet dropouts. The developed stability analysis and control scheme is also investigated with partially known transition probability matrices. Finally, a numerical example has been given to show the effectiveness of developed method. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance analysis of networked predictive control systems with data dropout

This paper is concerned with the design of networked control systems with random network data dropout. It presents a new control scheme, which is termed networked predictive control. This scheme mainly consists of the control prediction generator and network data dropout compensator. Besides, the control prediction generator provides a set of future control predictions to make the closed‐loop system achieve the desired control performance, and the network data dropout compensator removes the effects of the network transmission data dropout. Simulation results are presented to illustrate the effectiveness of the control strategy via comparing with other three existing control schemes. Copyright © 2012 John Wiley & Sons, Ltd.     

H∞ control of switched linear discrete‐time systems with polytopic uncertainties

In this paper, the problem of designing H_∞ state‐feedback controllers for switched linear discrete‐time systems with polytopic uncertainties is investigated. Two approaches on designing robust and parameter‐dependent H_∞ controllers are proposed and the existence conditions of the desired controllers are derived and formulated in terms of a set of linear matrix inequalities. By solving the corresponding convex optimization problem, the desired controllers are obtained, respectively, and different optimal H_∞ noise‐attenuation level bounds of corresponding closed‐loop systems are given as well. The designed controllers have their own advantages and disadvantages regarding the conservatism and realization complexity. An illustrative example emerging in networked control systems (NCS) and numerical simulations are presented to show the applicability and effectiveness of the obtained theoretic results. Copyright © 2006 John Wiley & Sons, Ltd.     

Adaptive fault tolerant control design for Takagi–Sugeno fuzzy systems with interval time‐varying delay

This paper deals with the problem of fault‐tolerant control (FTC) of continuous‐time Takagi–Sugeno fuzzy systems with interval time‐varying delay by using adaptive observer. Through constructing an appropriate type of Lyapunov function, a delay‐dependent criterion is established to reduce the conservatism of designing an active FTC (AFTC). In comparison with the existing techniques in the literature, the proposed approach simplifies the design of an AFTC and gives in only one step of the estimate of state vector, the estimate of actuator fault and the controller gains. Some simulation examples are included to demonstrate the effectiveness of the proposed approach. Copyright © 2013 John Wiley & Sons, Ltd.     

Observer‐based actuator fault estimation and proportional derivative fault tolerant control for continuous‐time singular systems

This paper focuses on designing fault estimation (FE) and fault tolerant control (FTC) schemes for continuous‐time singular systems affected by actuator fault. A novel observer called the extended proportional integral observer (PIO) is designed so that the estimations of system state and actuator fault can be obtained simultaneously. In contrast with the traditional PIO, better estimation performance can be obtained by using the designed observer. Furthermore, with the obtained FE information, a novel proportional derivative–type FTC scheme is given by means of the separation property and the free‐weighting matrix technique, which ensures that the closed‐loop system is normal and stable. All the feasible conditions are formulated in linear matrix inequality (LMI) frameworks. Finally, two examples are simulated to prove the superiority and practicability of the presented scheme.     

Reliable control for interval time‐varying delay systems subjected to actuator saturation and stochastic failure

This paper is devoted to the problem of reliable control for interval time‐varying delay systems subjected to actuator saturation and stochastic failure. A new practical actuator fault model is proposed by assuming that the actuator fault obeys a certain probabilistic distribution. An optimization problem with LMI constraints is formulated to determine the largest contractively invariant ellipsoid. Delay distribution and fault distribution‐dependent estimations of the domain of attraction are obtained by using the LMI techniques and an optimization method, such that the mean‐square stability of the systems can be guaranteed for given H_∞ performance index γ. Two illustrative examples are exploited to show the effectiveness of the proposed design procedures. Copyright © 2011 John Wiley & Sons, Ltd.     

Set‐valued observer‐based active fault‐tolerant model predictive control

This paper proposes an integrated actuator and sensor active fault‐tolerant model predictive control scheme. In this scheme, fault detection is implemented by using a set‐valued observer, fault isolation (FI) is performed by set manipulations, and fault‐tolerant control is carried out through the design of a robust model predictive control law. In this paper, a set‐valued observer is used to passively complete the fault detection task, while FI is actively performed by making use of the constraint‐handling capability of robust model predictive control. The set‐valued observer is chosen to implement fault detection and isolation (FDI) because of its simple mathematical structure that is not affected by the type of faults such as sensor, actuator, and system‐structural faults. This means that only one set‐valued observer is needed to monitor all considered actuator and sensor statuses (health and fault) and to carry out the fault detection and isolation task instead of using a bank of observers (each observer matching a health/fault status). Furthermore, in the proposed scheme, the advantage of robust model predictive control is that it can effectively deal with system constraints, disturbances, and noises and allow to implement an active FI strategy, which can improve FI sensitivity when compared with the passive FI methods. Finally, a case study based on the well‐known two‐tank system is used to illustrate the effectiveness of the proposed fault‐tolerant model predictive control scheme. Copyright © 2016 John Wiley & Sons, Ltd.     

Optimal guaranteed cost stabilization of networked systems with bounded random packet losses

This paper is concerned with the optimal guaranteed cost stabilizing controller design problem for a class of networked control systems (NCSs) with random packet losses. The number of consecutive packet losses is assumed to be upper bounded, and the closed‐loop NCS is described as a discrete‐time stochastic delay system with a time‐varying input delay and a stochastic parameter. A sufficient condition is derived for the closed‐loop NCS to be exponentially stable and achieve an optimal guaranteed cost performance level. The relationships among the exponential decay rate, the guaranteed cost performance level, and two parameters characterizing the random packet losses, namely, the packet loss probability and the maximal number of consecutive packet losses, are simultaneously established in the obtained condition. Furthermore, design procedures for the state feedback stabilizing controllers are also presented. Finally, an illustrative example is given to show the effectiveness of the proposed results. Copyright © 2011 John Wiley & Sons, Ltd.     

Nonfragile H∞ fault detection for fuzzy discrete systems under stochastic communication protocol

In this article, considering one type of fuzzy discrete‐time networked control systems (NCSs) under stochastic communication protocol (SCP), a fuzzy‐based nonfragile H_∞ filter is developed to detect the subsistent fault signal. The Takagi‐Sugeno (T‐S) mathematical model is employed to approximate the nonlinearities in the concerned fuzzy NCSs. The SCP is adopted to decide which sensor gets the access to the communication network at certain time instant, and the scheduling model of which is constructed as a Markov chain. Taking into account that the filter gain parameters in real practice may suffer fluctuations during the implementation, a modified nonfragile fuzzy filter is designed to detect the fault occurred in the signal transmission. By using the strong centralized stochastic analysis technique and the matrix calculation method, a Lyapunov function is adopted to derive sufficient conditions under which the filtering error dynamics is stochastically stable and the H_∞ performance is satisfied. Then, the desired nonfragile fuzzy fault detection filter is realized by solving a certain linear matrix inequality. Finally, the effectiveness of the develop fault detection scheme is verified in the simulation example.     

Simultaneous fault detection and control design for switched linear systems based on dynamic observer

The problem of simultaneous fault detection and control (SFDC) for linear continuous‐time switched systems is addressed in this paper. An H _∞ formulation of the SFDC problem using dynamic observer is presented. In essence, a single unit called detector/controller depending on the system modes is designed, where the detector is a dynamic observer, and the controller is a state feedback controller based on the dynamic observer. It is shown that the dynamic observer can be used effectively to tackle the drawbacks of the existing methods of SFDC design. Extended linear matrix inequalities (LMIs) characterization is used to reduce the conservativeness by introducing additional matrix variables, so as to eliminate the coupling of Lyapunov matrices with the system matrices. Indeed, the idea presented in this paper is based on average dwell time and conservatism reduction approaches and applying the advantages of dynamic observers, which leads to some sufficient conditions for solvability of the SFDC problem in terms of LMI feasibility conditions. Simulation results illustrate the effectiveness of the proposed design methodology. Copyright © 2011 John Wiley & Sons, Ltd.