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Online ISSN 1751-8652 Print ISSN 1751-8644

IET Control Theory & Applications

Volume 4, Issue 11, November 2010

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Volume 4, Issue 11

November 2010

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  • Regular Papers

    • Improved sliding mode control for discrete-time systems via reaching law
      Quantised robust ℋ∞ output feedback control of discrete-time systems with random communication delays
      • Author(s): F. Rasool  and  S.K. Nguang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2252 –2262
      • DOI:  10.1049/iet-cta.2009.0222
      • Type: Article
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      • p. 2252 –2262 (11)
        In this study, a stability criterion and robust ℋ∞ mode delay-dependent quantised dynamic output feedback controller design problem for discrete-time systems with random communication delays, packet dropouts and quantisation errors are investigated. Random communication delays from the sensor to controller network are modelled using a finite-state Markov chain with a special transition probability. A logarithmic quantiser is used to quantise the measured output. The Lyapunov–Krasovskii (L–K) functional approach is used to derive the stochastic stability criterion for the system with a given attenuation level. Sufficient conditions for the existence of an output feedback controller is formulated in terms of bilinear matrix inequalities (BMIs). Owing to the special transition probability matrix, a new slack matrix is added to BMIs to relax the sufficient conditions for the existence of an output feedback controller. Furthermore, an iterative algorithm is used to convert the BMIs into the quasi-convex optimisation problem which can be solved easily. An example is given to demonstrate the effectiveness of the proposed design.
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      Using a Kalman filter and a Padé approximation to estimate random time delays in a networked feedback control system
      • Author(s): A. Probst ; M.E. Magaña ; O. Sawodny
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2263 –2272
      • DOI:  10.1049/iet-cta.2009.0339
      • Type: Article
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      • p. 2263 –2272 (10)
        This study presents an effective algorithm to handle time delays in a feedback control loop in which both the measurement signals and the control signals are sent through a network where random time delays and packet loss occur. A method is developed to estimate the random time delay when no time stamps are present. Specifically, a Padé approximation is used to model time delay in the frequency domain, which can then be estimated by a Kalman filter. The method is applied to an inverted pendulum, where its effects are illustrated.
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      New approach to H∞ control for Markovian jump singular systems
      • Author(s): J. Zhang ; Y. Xia ; E.K. Boukas
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2273 –2284
      • DOI:  10.1049/iet-cta.2009.0231
      • Type: Article
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      • p. 2273 –2284 (12)
        This study investigates the H∞ control problem for a class of continuous-time Markovian jump singular systems. The authors' attention is focused on the design of state and static output feedback controllers which ensure that the closed-loop system is regular, impulse-free and stochastically stable, and satisfies a prescribed H∞ performance level. To investigate the problem of H∞ performance analysis for the system under consideration, a bounded real lemma (BRL) is provided in terms of linear matrix inequality (LMI) containing equality constraints, which may not be a problem from the theoretical point of view, but may cause great big trouble in checking the conditions numerically. To solve this problem, a new version of BRL is also provided in terms of strict LMIs. Based on this, two approaches are established to solve the problem of state feedback H∞ control, and then, the problem of static output feedback H∞ control is solved, which can also be used for solving the dynamic output feedback control problems. Finally, two numerical examples are given to illustrate the effectiveness of the obtained theoretical results.
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      Chaotic synchronisation using output/full state-feedback polynomial controller
      • Author(s): H.K. Lam
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2285 –2292
      • DOI:  10.1049/iet-cta.2009.0328
      • Type: Article
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      • p. 2285 –2292 (8)
        This study presents the synchronisation of two chaotic systems, namely drive and response chaotic systems, using polynomial controllers. Both output and full state-feedback polynomial controllers are proposed, respectively, to drive the system states of the response system to approach those of the drive one. The system stability of the overall system is investigated by the Lyapunov stability theory. Stability conditions in terms of sum of squares (SOS) are derived to aid the design of the feedback gains of the polynomial controllers. By satisfying the SOS-based stability conditions, chaotic synchronisation is achieved with system performance guaranteed by an H∞ performance function. Simulation examples are given to illustrate the merits of the proposed polynomial control approach.
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      Studies on linear matrix inequality relaxations for fuzzy control systems via homogeneous polynomials
      • Author(s): J.-C. Lo  and  J.-R. Wan
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2293 –2302
      • DOI:  10.1049/iet-cta.2009.0192
      • Type: Article
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      • p. 2293 –2302 (10)
        In this study, the authors investigate a relaxed condition characterised by parameter-dependent linear matrix inequality (PD-LMI) in terms of firing strength belonging to the unit simplex, exploiting the algebraic property of Pólya's theorem to construct a family of finite-dimensional LMI relaxations. The main contribution of this study is that sets of relaxed LMI are parameterised in terms of the polynomial degree d. As d increases, progressively less conservative LMI conditions are generated, being easier satisfied owing to more freedom provided by new variables involved. Another protruding feature is that a verifiable necessary condition is derived. Furthermore, the new relaxation results for PD-LMI is shown to include and generalise all previous results on quadratic (common P) stability approach. Lastly, numerical experiments for illustrating the advantage of relaxation, being less conservative and effective, are provided.
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      H∞ fault detection for linear discrete time-varying systems with delayed state
      • Author(s): H. Zhao ; M. Zhong ; M. Zhang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2303 –2314
      • DOI:  10.1049/iet-cta.2009.0215
      • Type: Article
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      • p. 2303 –2314 (12)
        This study deals with the problem of H∞ fault detection for linear discrete time-varying systems with delayed state in the framework of H∞ filtering. The design of the H∞ fault detection filter (FDF) is firstly converted into the minimum problem of an indefinite quadratic form. After introducing a corresponding Krein space stochastic system and building a relationship with projection, a sufficient and necessary condition on the existence of the minimum is derived by applying innovation analysis. A solution to the H∞-FDF is obtained in terms of matrix difference equations. Numerical examples are given to demonstrate the effectiveness of the proposed method.
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      Piecewise affine model-based H∞ static output feedback control of constrained non-linear processes
      • Author(s): J. Qiu ; T. Zhang ; G. Feng ; H. Liu
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2315 –2330
      • DOI:  10.1049/iet-cta.2009.0235
      • Type: Article
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      • p. 2315 –2330 (16)
        This study develops two efficient static output feedback (SOF) control approaches for a class of constrained non-linear processes represented by uncertain piecewise affine models. The parameter uncertainties in the piecewise affine models are assumed to be time varying and norm bounded. With the aid of the congruence transformation, degenerate ellipsoids-based -procedure, and some bounding inequalities, the piecewise SOF controller can be easily obtained by solving a convex semi-definite programming problem subject to some linear matrix inequalities. The resulting closed-loop system stability can be guaranteed as well as the H∞ control performance, and the stabilising design is less conservative owing to the piecewise quadratic Lyapunov functions. The performance of the proposed control approaches are demonstrated by simulation results on a non-linear benchmark plant.
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      Feedback process scheduling with simple discrete-time control structures
      • Author(s): A. Leva  and  M. Maggio
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2331 –2342
      • DOI:  10.1049/iet-cta.2009.0260
      • Type: Article
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      • p. 2331 –2342 (12)
        This manuscript addresses the problem of process scheduling in a multitasking computing environment. The mainstream feedback-based approach to that problem preserves the existing scheduler, and adapts some of its parameters by means of convenient loops. On the contrary, in this research, the scheduler is entirely replaced by suitable control structures, synthesised and analysed in the discrete-time domain. The proposed approach allows for a clear interpretability of the involved parameters, whereas the complexity of the obtained scheduling solutions is comparable to the existing ones. Simulation examples support the above claims. The focus is here restricted for convenience to the preemptive single-processor case, although several generalisations are possible.
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      Trajectory tracking control design with command-filtered compensation for a quadrotor
      • Author(s): Z. Zuo
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2343 –2355
      • DOI:  10.1049/iet-cta.2009.0336
      • Type: Article
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      • p. 2343 –2355 (13)
        The design of a flight control system capable of not only stabilising attitude but also tracking a trajectory accurately for an under-actuated quadrotor aircraft is quite challenging. This study constructs the relationship between the attitude and linear acceleration of a small quadrotor unmanned aircraft and proposes a trajectory tracking control design algorithm, based on the relationship, using a new command-filtered backstepping technique to stabilise the attitude and a linear tracking differentiator to eliminate the classical inner/outer-loop structure. Finally, the validity and the effectiveness of this algorithm are demonstrated by various numerical simulations under different conditions.
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      Motion control of mobile under-actuated manipulators by implicit function using support vector machines
      • Author(s): Z. Li ; J. Zhang ; Y. Yang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2356 –2368
      • DOI:  10.1049/iet-cta.2009.0200
      • Type: Article
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      • p. 2356 –2368 (13)
        In this study, the authors propose implicit control using least square support vector machines (LS-SVMs) approximation for the motion control of wheeled under-actuated manipulators. For approximating the multi-input and multi-output non-linear system, an LS-SVM matrix operator is proposed. Further, by using implicit function with SVMs, a control is constructed to obtain motion tracking of wheeled under-actuated manipulators. The relative degree of the regulated output is assumed to be known enabling the system feedback linearisable. It is shown that the tracking error can be controlled in a small neighbourhood of zero through Lyapunov's direct method. The methodology is applicable to minimum phase observable and stabilisable systems of unknown but finite dimension, as long as the relative degree is known. The effectiveness of the proposed control method is substantiated by the simulation results.
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      Position-tracking control of underactuated autonomous underwater vehicles in the presence of unknown ocean currents
      • Author(s): F.Y. Bi ; Y.J. Wei ; J.Z. Zhang ; W. Cao
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2369 –2380
      • DOI:  10.1049/iet-cta.2009.0265
      • Type: Article
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      • p. 2369 –2380 (12)
        This study addresses the problem of position-tracking control of underactuated autonomous underwater vehicles (AUVs) in the presence of unknown ocean currents in a horizontal plane. A position-tracking controller and a current observer are presented based on the Lyapunov stability theory by using the backstepping technique, respectively. The final controlled system, which arises from putting together the position-tracking controller and the observer, is proved to be globally K-exponentially stable by stability criteria for cascade system. The trajectories used for the illustration of the proposed control schemes are a circle with constant velocity and a sinusoidal curve that requires time-varying velocity. In order to demonstrate the practicability of the proposed controller, the surge force is assumed to be non-negative, and control input saturations are considered. Simulation results are presented to demonstrate the effectiveness of the proposed control schemes.
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      Isomorphism-based robust right coprime factorisation of non-linear unstable plants with perturbations
      • Author(s): M. Deng  and  N. Bu
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2381 –2390
      • DOI:  10.1049/iet-cta.2009.0297
      • Type: Article
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      • p. 2381 –2390 (10)
        This study is concerned with the robust right coprime factorisation of non-linear plants based on the isomorphism approach. First, the factorisation of the non-linear plant is realised by using the isomorphism approach where the Bezout identity is simply satisfied with the obtained factors. Moreover, the stability of the non-linear feedback system and the output tracking to the reference input are studied. The effectiveness of the proposed method is demonstrated by the simulations.
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      Repetitive controller for time-delay systems based on disturbance observer
      • Author(s): J. Na ; R. Griñó ; R. Costa-Castelló ; X. Ren ; Q. Chen
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2391 –2404
      • DOI:  10.1049/iet-cta.2009.0411
      • Type: Article
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      • p. 2391 –2404 (14)
        A novel continuous time repetitive control design is presented for time-delay systems with periodic references and disturbances. Taking profit of the system model and an appropriate time-delay, an inner positive feedback loop is constructed to establish an internal model for periodic signals, and a simple proportional control is utilised in the outer feedback loop to stabilise the closed-loop system. Thus, the tracking capability can be guaranteed according to internal model principle. In addition, to compensate for the effect of external periodic disturbances, a disturbance observer using the system model and a model-based compensator is introduced inside the proposed internal model such that the tracking and disturbance rejection can be achieved simultaneously. Sufficient stability conditions and the robustness analysis under modelling uncertainties are all studied. Only two parameters are needed to be chosen by the designer. Numerical examples and practical experiments on a motor control system are included to illustrate the feasibility and simplicity of the proposed methods.
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      Global exponential stability criteria for neural networks with probabilistic delays
      • Author(s): M.S. Mahmoud ; S.Z. Selim ; P. Shi
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2405 –2415
      • DOI:  10.1049/iet-cta.2009.0007
      • Type: Article
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      • p. 2405 –2415 (11)
        The problem of global exponential stability analysis for a class of neural networks (NNs) with probabilistic delays is discussed in this paper. The delay is assumed to follow a given probability density function. This function is discretised into arbitrary number of intervals. In this way, the NN with random time delays is transformed into one with deterministic delays and random parameters. New conditions for the exponential stability of such NNs are obtained by employing new Lyapunov–Krasovskii functionals and novel techniques for achieving delay dependence. It is established that these conditions reduce the conservatism by considering not only the range of the time delays, but also the probability distribution of their variation. Numerical examples are provided to show the advantages of the proposed techniques.
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      Agreement over noisy networks
      • Author(s): A.K. Das ; Y. Hatano ; M. Mesbahi
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2416 –2426
      • DOI:  10.1049/iet-cta.2009.0394
      • Type: Article
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      • p. 2416 –2426 (11)
        The authors consider the agreement problem over noisy communication networks. This problem is analysed via a blend of ideas from stochastic stability (supermartingales) and algebraic graph theory (spectra of graph Laplacians). In this venue, the authors show that the noisy agreement protocol has a guaranteed probabilistic convergence, provided that an embedded step size meets a graph theoretic constraint. The authors then proceed to define a pertinent graph parameter and point out the ramifications of having noisy information exchange links in networks that can be modelled as random and random geometric graphs.
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      Design of robust optimal proportional–integral–derivative controller based on new interval polynomial stability criterion and Lyapunov theorem in the multiple parameters' perturbations circumstance
      • Author(s): X.H. Li ; H.B. Yu ; M.Z. Yuan ; J. Wang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2427 –2440
      • DOI:  10.1049/iet-cta.2009.0424
      • Type: Article
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      • p. 2427 –2440 (14)
        Based on the new interval polynomial stability criterion and Lyapunov theorem, a robust optimal proportional–integral–derivative (PID) controller is proposed here to design for different plants that contain the perturbations of multiple parameters. A new stability criterion of the interval polynomial is presented to determine whether the interval polynomial belongs to Hurwitz polynomial. The robust optimal PID controller is acquired through minimising an augmented integral squared error (AISE) performance index. The robust optimal control problem is transformed into a non-linear constraint optimisation (NLCO) problem by applying new polynomial stability criterion and Lyapunov approach. The robust optimal PID parameters are obtained from solving the NLCO problem. The robustness and performances of the proposed method and other different tuning methods are compared. The ability of the proposed PID tuning method and other tuning methods to reject disturbances is discussed as well. The simulation results are presented to demonstrate the effectiveness of the proposed method and show better robustness of the robust optimal PID controller.
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      Decentralised stabilisation of a class of large-scale high-order stochastic non-linear systems
      • Author(s): W. Li ; Y. Jing ; S. Zhang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2441 –2453
      • DOI:  10.1049/iet-cta.2009.0322
      • Type: Article
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      • p. 2441 –2453 (13)
        For a class of large-scale high-order stochastic non-linear systems which are neither necessarily feedback linearisable nor affine in the control input, this study investigates the decentralised stabilisation for the first time. Under some moderate assumptions, smooth decentralised state-feedback controllers are designed, which ensure that the closed-loop system has an almost surely unique solution on [0, ∞), the equilibrium at the origin of the closed-loop system is globally asymptotically stable (GAS) in probability, the states can be regulated to the origin almost surely, and the problem of inverse optimal stabilisation (IOS) in probability is solved. The efficiency of the control scheme is demonstrated by a simulation example.
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      Corrective control of asynchronous machines with uncontrollable inputs: application to single-event-upset error counters
      • Author(s): J.-M. Yang  and  S.W. Kwak
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2454 –2462
      • DOI:  10.1049/iet-cta.2009.0397
      • Type: Article
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      • p. 2454 –2462 (9)
        Corrective control of asynchronous sequential machines is to design a feedback controller so that the behaviour of the closed-loop asynchronous machine matches that of a prescribed model. This study proposes a control scheme for asynchronous machines with uncontrollable external inputs, over which the controlling agent has no influence. The existence condition for an appropriate controller and its design procedure are analytically presented. It is shown that an asynchronous machine must have additional reachability to achieve control objectives against transitions caused by uncontrollable inputs. In particular, the authors apply the proposed control scheme to implementing single-event-upset error counters used by error detection and correction circuits. The authors' result demonstrates that corrective control can be employed in real digital systems.
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      Global asymptotic stability of a class of complex networks via decentralised static output feedback control
      • Author(s): P. Lu  and  Y. Yang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2463 –2470
      • DOI:  10.1049/iet-cta.2009.0416
      • Type: Article
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      • p. 2463 –2470 (8)
        This study deals with the problem of the decentralised static output feedback for a class of dynamic networks with each node being a general Lur'e system. On the basis of the Kalman–Yakubovich–Popov (KYP) lemma, linear matrix inequality (LMI) conditions guaranteeing the stability of such dynamic networks are established. In addition, the following interesting result is derived: the stability problem for the whole Nn-dimensional dynamic networks can be converted into the simple n-dimensional space in terms of only two LMIs. Finally, a concrete application to mutually coupled phase-locked loop networks shows the validity of the proposed approaches.
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      Tracking under additive white Gaussian noise effect
      • Author(s): L. Ding ; H.-N. Wang ; Z.-H. Guan ; J. Chen
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2471 –2478
      • DOI:  10.1049/iet-cta.2009.0449
      • Type: Article
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      • p. 2471 –2478 (8)
        This study investigates the tracking performance of continuous-time, multi-input multi-output, linear time-invariant systems in which the output feedback is subject to an additive white Gaussian noise corruption. The problem under consideration amounts to determining the minimal error in tracking a Brownian motion random process, which emulates a step reference signal in the deterministic setting. The authors consider both the unity feedback and two-parameter control structure. In the former case, they derive an explicit bound, and in the latter an exact expression of the minimal tracking error attainable under the noise effect. Both results demonstrate how the additive white Gaussian noise may degenerate the tracking performance, and how the noise effect may intertwine with unstable poles and non-minimum phase zeros which are intrinsic characteristics of the plant.
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      2-Sliding active and reactive power control of a wind energy conversion system
      • Author(s): F. Valenciaga  and  C.A. Evangelista
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2479 –2490
      • DOI:  10.1049/iet-cta.2009.0437
      • Type: Article
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      • p. 2479 –2490 (12)
        This study presents the control of a variable-speed wind energy conversion system based on a brushless doubly fed reluctance machine. The control objectives are the tracking of the maximum power conversion point and the regulation of the reactive power injected by the generation system into the grid. The control design is approached using multi-input second-order sliding techniques which are specially appropriate to deal with non-linear system models in the presence of disturbances and model inaccuracies. The controller synthesised through this theoretical framework presents very good robustness features, a finite reaching time and a chattering-free behaviour. The performance of the closed-loop system is assessed through representative computer simulations.
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      H∞ design of rotor flux-oriented current-controlled induction motor drives: speed control, noise attenuation and stability robustness
      • Author(s): J.C. Basilio ; J.A. Silva ; L.G.B. Rolim ; M.V. Moreira
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2491 –2505
      • DOI:  10.1049/iet-cta.2009.0377
      • Type: Article
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      • p. 2491 –2505 (15)
        This study deals with the design of H∞ controllers for speed control of rotor flux-oriented current-controlled induction motors. The mixed sensitivity problem (robust stability and performance) is initially revisited, and is shown, based on practical experiments, that when the rotor time constant is the uncertain parameter, it is necessary to deploy conflicting weighting functions, therefore invaliding its application in the design of current-fed induction motors. Two other H∞ problems are addressed: (i) a one-block problem for speed control with tracking and transient performance objectives; and (ii) a two-block problem for speed control with tracking/transient performance and noise attenuation objectives. An important part of H∞ design is the model of the system to be controlled. In this study, the system composed of the inverter, estimator and induction motor will be modelled as a first-order system, and experiments for the identification of the gain and the time constant are proposed. It is also suggested how to properly correct an initial estimation of the rotor time constant in order to make the actual plant (inverter-induction motor) behave as a first-order linear system. The model accuracy and the efficiency of the H∞ controllers are validated by experiments carried out in a real system.
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      Reconfigurable system for real-time embedded control applications
      • Author(s): P. Patel  and  M. Moallem
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2506 –2515
      • DOI:  10.1049/iet-cta.2009.0471
      • Type: Article
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      • p. 2506 –2515 (10)
        This paper discusses the development of embedded controllers on a reconfigurable multiprocessor system using field programmable gate array (FPGA) technology. The system is reconfigurable in hardware and software in the sense that certain components may be reused in different applications, hence allowing rapid development of embedded control systems. Concurrent real-time operation can be achieved by utilising hardware and software modules consisting of dedicated hardware cores and real-time operating systems. For demonstration purposes, we discuss the development of a system consisting of a network-enabled master processor that handles two slave processors each controlling a mechatronic system. The user interface is implemented using an internet browser through the master processor which allows monitoring and supervisory control of the individual systems. A multi-threaded real-time operating system runs on each of the softcore processors which allows flexibility and modularity in software design whereas pre-designed hardware modules on the FPGA chip can be utilised for building comuting hardware for control applications. Experimental results are presented for illustrating how control applications can be developed and deployed using modular components and the hardware/software environment.
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      Adaptive sliding control with self-tuning fuzzy compensation for a piezoelectrically actuated X–Y table
      • Author(s): H.-Y. Chen  and  J.-W. Liang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2516 –2526
      • DOI:  10.1049/iet-cta.2009.0223
      • Type: Article
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      • p. 2516 –2526 (11)
        The piezoelectrically actuated system has non-linear and time-varying behaviour, hence it is difficult to establish an accurate dynamic model for a model-based sliding-mode control design. In this study, a model-free adaptive sliding controller is proposed to control the piezoelectrically actuated system. This control strategy uses the functional approximation (FA) technique to establish the unknown function for releasing the model-based requirement of the sliding-mode control. In addition, a fuzzy scheme with online learning ability is introduced to compensate the FA error for improving the control performance and reducing the implementation difficulty. The important advantages of this approach are to achieve the sliding-mode controller design without the system dynamic model requirement and release the trial-and-error work of selecting approximation function. The update laws for the coefficients of the Fourier series functions and the fuzzy tuning parameters are derived from a Lyapunov function to guarantee the control system stability. This proposed controller is implemented on a piezoelectrically actuated X–Y table. To verify the dynamic performance improvement of inducing a fuzzy compensation in this model-free controller, the dynamic responses of the proposed controller are compared with those of the adaptive sliding controller without fuzzy compensation.
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      Latent space transformation based on principal component analysis for adaptive fault detection
      • Author(s): P.C. Deng ; W.H. Gui ; Y.F. Xie
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2527 –2538
      • DOI:  10.1049/iet-cta.2008.0546
      • Type: Article
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      • p. 2527 –2538 (12)
        Principal component analysis (PCA) has been effectively applied in fault detection and in diagnosis of industrial processes to deal with a large number of variables with high correlations. However, normal changes often occur in real process, which always result in false alarms for a fixed-model approach. The authors' research is focused on the traits of normal process changes, which are classified into three scenarios, including process drifting, enlarging and bias, and then three latent space transformation-based PCA algorithms are proposed to obtain an adaptive model described by a new set of coordinates for adaptive fault detection. Finally, the proposed algorithms are applied to imperial smelting furnace.
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      Redundant adaptive robust tracking of active satellite and error evaluation
      • Author(s): Y.K. Li ; Z.L. Jing ; S.Q. Hu
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2539 –2553
      • DOI:  10.1049/iet-cta.2009.0319
      • Type: Article
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      • p. 2539 –2553 (15)
        An approach to active target satellite tracking is presented. The kinematic models based on differential orbital elements and unbiased converted measurements are adopted to approximate the dynamic orbital relative tracking system, and then followed by the proposed redundant adaptive robust extended Kalman filter (RAREKF). The analysis of working status of robust filters shows that the innovation controlled switching scheme in AREKF fails under the unmodelled non-linear errors that exist all the time in orbital motions, and the loss of filtering optimality will be caused. So, a tunable redundancy factor and a novel compensation function are introduced into the RAREKF by extending the sufficient conditions of stable filtering. To evaluate the result of this tracking method, a meaningful error index is provided by consideration of the errors from both the model and the filter. The simulation shows the superiority of the RAREKF over the AREKF, uncoupled extended Kalman filter (EKF) and the usual EKF. By using the provided index, it also illustrates the lowest error level and best performance of the proposed tracking method in all the compared ones with different models and filters.
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      Passive control for continuous singular systems with non-linear perturbations
      • Author(s): Y. Gao ; G. Lu ; Z. Wang
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2554 –2564
      • DOI:  10.1049/iet-cta.2009.0048
      • Type: Article
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      • p. 2554 –2564 (11)
        This study addresses the passivity analysis and passivity-based control for continuous singular systems with non-linear perturbations. The perturbations are the function of time and system state and satisfy the Lipschitz constraints. The passivity condition, which includes a sufficient condition for the existence-uniqueness of solution to the singular system and exponential stability, is expressed in terms of linear matrix inequalities (LMIs). The state feedback controller based on passivity is designed and the numerical example is presented to demonstrate the effectiveness of the proposed method.
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      Non-linear dual-mode receding horizon control for multiple unmanned air vehicles formation flight based on chaotic particle swarm optimisation
      • Author(s): H.B. Duan  and  S.Q. Liu
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2565 –2578
      • DOI:  10.1049/iet-cta.2009.0256
      • Type: Article
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      • p. 2565 –2578 (14)
        This study presents a non-linear dual-mode receding horizon control (RHC) approach to investigate the formation flight problem for multiple unmanned air vehicles (UAVs) under complicated environments. A chaotic particle swarm optimisation (PSO)-based non-linear dual-mode RHC method is proposed for solving the constrained non-linear systems. The presented chaotic PSO derives both formation model and its parameter values, and the control sequence is predicted in this way, which can also guarantee the global convergence speed. A dual-model control strategy is used to improve the stability and feasibility for multiple UAVs formation flight controller, and the state-feedback control is also adopted, where the model is based on the invariant set theory. Series experimental results show the feasibility and validity of the proposed control algorithm over other algorithms. The proposed approach is also a promising control strategy in solving other complicated real-world problems.
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      Co-ordinated collective motion patterns in a discrete-time setting with experiments
      • Author(s): Y. Cao ; D. Stuart ; W. Ren
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2579 –2591
      • DOI:  10.1049/iet-cta.2009.0338
      • Type: Article
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      • p. 2579 –2591 (13)
        In this study, the authors co-ordinated collective motion patterns for a group of autonomous vehicles with Cartesian co-ordinate coupling in a discrete-time setting and present experimental results to validate the theoretical results. The collective motion patterns include rendezvous, circular patterns and logarithmic spiral patterns. The authors first study the collective motion patterns for a group of autonomous vehicles with single-integrator kinematics in a discrete-time setting when there exists time delay. The conditions on the network topology, the sampling period, the time delay and the Euler angle are presented such that different collective motion patterns can be achieved. The collective motion patterns for a group of autonomous vehicles with double-integrator dynamics in a discrete-time setting in the presence of relative damping are studied. The conditions on the network topology, the sampling period, the damping factor and the Euler angle are presented such that different collective patterns can be achieved. Finally, the theoretical results are experimentally validated on a multi-robot platform.
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      Stability analysis of linear time-delay differential inclusion systems subject to input saturation
      • Author(s): X. Cai ; J. Huang ; L. Liu
      • Source: IET Control Theory & Applications, Volume 4, Issue 11, p. 2592 –2602
      • DOI:  10.1049/iet-cta.2009.0208
      • Type: Article
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      • p. 2592 –2602 (11)
        Stability analysis of linear differential inclusion systems with time-delay and input saturation is devoted in this study. The convex hull Lyapunov function is used to construct Lyapunov–Krasovskii functionals. A continuous state feedback law is designed. By the state feedbacks, sufficient conditions for saturated stabilisation are acquired and the domain of attraction is estimated. Furthermore, disturbance rejection with minimal reachable set is studied under two types of disturbances. Moreover, least L2 gain is obtained under the unit energy disturbances. Finally, two numerical examples are given to illustrate the effectiveness of the proposed design technique.
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