Control reconfiguration after actuator failures by Markov parameter matching

Two novel linear control reconfiguration methods for plants subject to actuator failures are described. The common idea is to place a reconfiguration block between the faulty plant and the nominal controller in order to re-route the signals around the broken actuator. The first method uses a computationally simple static reconfiguration block. It recovers the nominal plant input/output-behaviour by assigning the faulty plant the same Markov parameters as the faultless plant. The second method concerns the design of the feedforward part in the virtual actuator using the idea and results of the first approach. The virtual actuator is a dynamical reconfiguration block. Existence conditions and solution algorithms are provided, and it is shown that both approaches guarantee the closed-loop stability if the existence conditions are met. An experimental study demonstrates the practical usability of the proposed approaches.     

Command-filter-based distributed containment control of nonlinear multi-agent systems with actuator failures

In this paper, the problem of distributed containment fault-tolerant control for a class of nonlinear multi-agent systems in strict-feedback form is studied. The considered nonlinear multi-agent systems are subject to unknown nonlinear functions and actuator faults with loss of effectiveness and lock-in-place. By resorting to the universal approximation capability of fuzzy logical systems, the command filtered backstepping technique and nonlinear fault-tolerant control theory, distributed controllers are designed recursively. From the Lyapunov stability theory, it is proved that all signals of the resulting closed-loop systems are cooperatively semi-globally uniformly ultimately bounded and the containment errors converge to a small neighbourhood of origin by properly tuning the design parameters. Finally, a numerical example is provided to show the effectiveness of the proposed control method.     

Adaptive fuzzy decentralised fault-tolerant control for nonlinear large-scale systems with actuator failures and unmodelled dynamics

This paper discusses the adaptive fuzzy decentralised fault-tolerant control (FTC) problem for a class of nonlinear large-scale systems in strict-feedback form. The systems under study contain the unknown nonlinearities, unmodelled dynamics, actuator faults and without the direct measurements of state variables. With the help of fuzzy logic systems identifying the unknown functions and a fuzzy adaptive observer is designed to estimate the unmeasured states. By using the backstepping design technique and the dynamic surface control approach and combining with the changing supply function technique, a fuzzy adaptive FTC scheme is developed. The main features of the proposed control approach are that it can guarantee the closed-loop system to be input–to-state practically stable, and also has the robustness to the unmodelled dynamics. Moreover, it can overcome the so-called problem of ‘explosion of complexity’ existing in the previous literature. Finally, simulation studies are provided to illustrate the effectiveness of the proposed approach.     

考虑执行器故障的不确定线性系统可靠跟踪控制

针对具有不确定性的线性定常系统，提出了考虑执行器故障的可靠跟踪控制器设计问题．在更一般且更实际的执行器故障模型基础上，给出了系统输出渐近跟踪参考输入的可靠跟踪控制存在的充分条件，通过求解LMI完成状态反馈可靠控制器的设计，仿真实例验证了该设计方法的可行性，并且通过与不考虑故障的正常控制系统的比较，进一步说明对系统进行可靠跟踪控制的必要性。     

具有执行器故障的不确定多智能体系统自适应动态面控制

本文研究了一类具有输入量化、未建模动态和执行器故障的非线性多智能体系统的一致跟踪问题.引入一个可量测的动态信号消除未建模动态对系统的影响.利用Young’s不等式和高斯函数的性质,有效地处理了多智能体邻居节点在设计的第一步中对子系统的耦合作用.通过将滞回量化器表示为具有有界系数和有界扰动的输入线性函数,并利用动态面控制方法,提出一种自适应神经网络动态面控制方案,简化了控制器的设计,保证了闭环系统的所有信号都是半全局一致终结有界的,所有跟随者都能实现期望的一致性.最后,仿真结果验证了所提出的自适应控制策略的有效性.     

Reliable guaranteed-cost control for networked systems with randomly occurring actuator failures and fading performance output

This paper is concerned with the reliable guaranteed-cost control problem for a class of time-varying networked systems with randomly occurring actuator failures and fading performance output. The randomly occurring actuator failure, which describes the phenomenon of the actuator failure appearing in a random way, is modelled by a Bernoulli distributed white sequence with a known conditional probability. The fading performance output is characterized by a random variable obeying any discrete-time probability distribution over a known interval. The main purpose is to design a reliable controller over a given finite horizon such that, an optimized upper bound of the predefined quadratic performance index is guaranteed for the addressed systems in the presence of both the randomly occurring actuator failures and the fading performance output. It is shown that the desired controller gain can be obtained in terms of the solution to a Riccati-like difference equation. A numerical example is provided to illustrate the feasibility and effectiveness of the proposed control scheme.     

Fault-tolerant control of delta operator systems with actuator saturation and effectiveness loss

This paper studies the problem of robust fault-tolerant control against the actuator effectiveness loss for delta operator systems with actuator saturation. Ellipsoids are used to estimate the domain of attraction for the delta operator systems with actuator saturation and effectiveness loss. Some invariance set conditions used for enlarging the domain of attraction are expressed by linear matrix inequalities. Discussions on system performance optimisation are presented in this paper, including reduction on computational complexity, expansion of the domain of attraction and disturbance rejection. Two numerical examples are given to illustrate the effectiveness of the developed techniques.     

Switching event-triggered control of switched systems with actuator saturation

This paper focuses on switching event-triggered controller design for switched continuous-time systems with actuator saturation. First, we revisit the switching event-triggered sampled-data mechanism (ETSDM) to adapt it to the state feedback control of switched systems with actuator saturation. Then, by thinking of the ETSDM as a switching between periodic sampling and continuous ETSDM, constructing a switching multiple Lyapunov functions to give the analysis and design, and adopting the sector conditions to deal with the saturation, the sufficient conditions and the initial region ensuring the exponential stability of the switched system are proposed. Furthermore, the corresponding solvable conditions for the switching event-triggered controller and the triggering parameter matrices are established. Finally, a circuit example is given to illustrate the validity of the proposed results.     

Reconfigurable control of piecewise affine systems with actuator and sensor faults: Stability and tracking

A reconfigurable control approach for continuous-time piecewise affine (PWA) systems subject to actuator and sensor faults is presented. The approach extends the concept of virtual actuators and virtual sensors from linear to PWA systems on the basis of the fault-hiding principle that provides the underlying conceptual idea: the fault is hidden from the nominal controller and the fault effects are compensated. Sufficient linear matrix inequality (LMI) conditions for the existence of virtual actuators and virtual sensors are given that guarantee the recovery of closed-loop stability and the tracking of constant reference inputs. Since LMIs are efficiently solvable, this solution leads to a tractable computational algorithm that solves the reconfiguration problem. The approach is proven to be robust against model uncertainties and inaccurate fault diagnosis, and is evaluated using an example system of interconnected tanks.     

Supervisory switching‐based prescribed performance control of unknown nonlinear systems against actuator failures

This article studies the fault‐tolerant control problem for unknown nonlinear strict‐feedback systems subject to actuator failures yet with dynamic redundancies. The prescribed performance control methodology is newly combined with a modification‐based supervisory switching strategy to solve the problem. To implement failure detection, the performance function is properly modified to synthesize a monitoring function to supervise the behavior of an error variable. Once a failure is detected, the current actuator is shut down and the backup actuator is switched in to execute the reconfigured control command. Compared with the existing results, (1) the postfailure and postswitching tracking performance is improved, other than uniform ultimate boundedness and (2) the dependence on extra robust control schemes (eg, adaptive or approximating structures) to deal with model uncertainties or the need to compute analytic derivatives of virtual control signals in the backstepping design is eliminated.     

Bumpless switching control for switched systems with partial actuator failures

This study is concerned with the bumpless transfer problem for switched systems with partial actuator failures, in order to obtain smooth system performance output transition. Taking into account that the system requires a controller switching from current sub-controller to a fault-tolerant sub-controller after actuator fault. And bumpless transfer for control input cannot be traditionally designed when the actuator fault occurs, while performance smoothing can be considered and it is actually the ultimate goal of bumpless transfer. Specifically, the actuator fault model is firstly established and partial actuator fault is considered. Then, the system performance output signal is deemed as the main design variable of bumpless transfer, and closed-loop control systems both previous and after controller switching are constructed. Moreover, by using model matching thought and the adaptive sliding mode control technique, a bumpless transfer compensator design strategy is given to drive the performance output variable (after controller switching) to track the one of reference model. At last, simulation results of numeric and application examples demonstrate the effectiveness of the proposed bumpless transfer strategy.     

Dual-mode predictive control algorithm for constrained Hammerstein systems

In the process industry, there exist many systems which can be approximated by a Hammerstein model. Moreover, these systems are usually subjected to input magnitude constraints. In this paper, a multi-channel identification algorithm (MCIA) is proposed, in which the coefficient parameters are identified by least squares estimation (LSE) together with a singular value decomposition (SVD) technique. Compared with traditional single-channel identification algorithms, the present method can enhance the approximation accuracy remarkably, and provide consistent estimates even in the presence of coloured output noises under relatively weak assumptions on the persistent excitation (PE) condition of the inputs. Then, to facilitate the following controller design, this MCIA is converted into a two stage single-channel identification algorithm (TS-SCIA), which preserves most of the advantages of MCIA. With this TS-SCIA as the inner model, a dual-mode non-linear model predictive control (NMPC) algorithm is developed. In detail, over a finite horizon, an optimal input profile found by solving a open-loop optimal control problem drives the non-linear system state into the terminal invariant set; afterwards a linear output-feedback controller steers the state to the origin asymptotically. In contrast to the traditional algorithms, the present method has a maximal stable region, a better steady-state performance and a lower computational complexity. Finally, simulation results on a heat exchanger are presented to show the efficiency of both the identification and the control algorithms.     

Networked predictive control for Hammerstein systems

This paper is concerned with the problems of design and stability analysis of networked predictive control for Hammerstein systems. The Hammerstein nonlinearity is removed (or partially removed) by inverting it. By predicting the future control sequence, the random network‐induced delay and data dropout are compensated actively. The stability of the closed‐loop system is analyzed by applying the switched Lyapunov function approach. Simulation results are presented to illustrate the validity of the proposed method. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Stabilization of uncertain networked control systems with actuator saturation and probabilistic cyberattacks

This paper investigates the stabilization of uncertain networked control systems (NCSs) with actuator saturation and cyberattacks. The cyberattacks are governed by a set of independent random variables satisfying Bernoulli distribution. To relieve the network bandwidth load effectively, an event-triggered communication strategy is proposed. By employing Lyapunov stability theory and stochastic analysis techniques, a stability criterion is obtained for the system with actuator saturation and cyberattacks. Moreover, the desired controller gain is derived by solving some matrix inequalities. Finally, the validity and applicability of the criteria are verified through numerical examples.     

Event-triggered control for switched systems in the presence of actuator saturation

In this paper, the event-triggered stabilisation problem for a class of switched systems with actuator saturation is investigated. Based on multiple Lyapunov function method and the average dwell time approach, a sufficient condition for exponential stability of such systems under event-triggered state-feedback controller is derived. To avoid Zeno behaviour, it is shown that there exists a positive lower bound for any two consecutive inter-event instants. Finally, two examples are presented to illustrate the effectiveness of the proposed method.     

Adaptive stabilisation of networked control systems tolerant to unknown actuator failures

In this article, adaptive state feedback stabilising controllers for networked adaptive control systems with unknown actuator failures are developed. The problems of networked control systems (NCSs) such as transmission delays and data-packets dropout, induced by the insertion of data networks in the feedback adaptive control loops are also considered. The novelty of this article consists in the combination of different aspects in NCSs: state tracking control of systems with unknown parameters, unknown actuator failures, network-induced delays and data-packets dropout. Normalised adaptive laws are designed for updating the controller parameters. Sufficient conditions for Lyapunov stability are derived in the case of uncertainty due to actuator failures, delays and data-packets dropout. Simulation results are given to illustrate the effectiveness of our design approach.     

Semi‐global containment control for linear systems in the presence of actuator position and rate saturation

This paper studies the semi‐global containment control problem for a group of general linear systems in the presence of actuator position and rate saturation. Both a state feedback containment control algorithm and an output feedback containment algorithm are constructed for each follower agent in the system by using low gain approach. We show that the states of all follower agents will converge to the convex hull formed by the leader agents asymptotically under these control algorithms when the communication topology among follower agents is a connected undirected graph and each leader agent is a neighbor of at least one follower agent. Simulation results illustrate the theoretical results.     

Adaptive output-feedback control for a class of nonlinear systems with actuator failures and input quantisation

In this paper, an adaptive output feedback control technique is proposed for a class of nonlinear systems with unknown parameters, unknown nonlinear functions, quantised input and possible actuator failures up to infinity. A modified backstepping approach is proposed by the use of high-gain K-filters, hyperbolic tangent function property and bound-estimation approach to compensate for the effect of possible number of actuator failures up to infinity, input quantisation and unknown nonlinear functions. It is proved both mathematically and by simulation that with the proposed controller, all the signals of the closed-loop system are globally bounded despite of input quantisation, unknown nonlinear functions and possible number of actuator failures up to infinity.     

A stability guaranteed active fault‐tolerant control system against actuator failures

In this paper, a new strategy for fault‐tolerant control system design has been proposed using multiple controllers. The design of such controllers is shown to be unique in the sense that the resulting control system neither suffers from the problem of conservativeness of conventional passive fault‐tolerant control nor from the risk of instability associated with active fault‐tolerant control in case that an incorrect fault detection and isolation decision is made. In other words, the stability of the closed‐loop system is always ensured regardless of the decision made by the fault detection and isolation scheme. A correct decision will further lead to optimal performance of the closed‐loop system. This paper deals with the conflicting requirements among stability, redundancy, and graceful degradation in performance for fault‐tolerant control systems by using robust control techniques. A detailed design procedure has been presented with consideration of parameter uncertainties. Both total and partial actuator failures have been considered. This new control strategy has been demonstrated by controlling a McDonnell F‐4C airplane in the lateral‐direction through simulation. Copyright © 2004 John Wiley & Sons, Ltd.