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Control Theory & Applications, IET

Issue 1 • Date January 6 2011

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Displaying Results 1 - 25 of 25
  • Delay-dependent l2-L α filter design for stochastic time-delay systems

    Page(s): 1 - 8
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    This study considers the problem of delay-dependent L2-L filter design for a class of stochastic time-delay systems. Attention is focused on the design of an L2-L filter to guarantee a prescribed energy-to-peak performance for the filtering error system. Both full-order and reduced-order filter design approaches are obtained in terms of linear matrix inequalities. Finally, a numerical example is provided to illustrate the effectiveness and improvement of the proposed filter design methods over some existing results. View full abstract»

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  • Simultaneous Hα control for continuous-time descriptor systems

    Page(s): 9 - 18
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (253 KB)  

    This study addresses the simultaneous H control problem for continuous-time descriptor systems, namely, a single controller is sought to stabilise a collection of descriptor systems with a prescribed H norm. First, this problem is transformed equivalently to the strong H stabilisation problem of an augmented system. Then, a sufficient condition of the existence of strongly admissible H controllers is proposed in terms of strict linear matrix inequalities. Finally, numerical examples are presented to show the effectiveness of the proposed method. View full abstract»

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  • Dynamic consensus of linear multi-agent systems

    Page(s): 19 - 28
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (282 KB)  

    This study concerns the consensus of a network of agents with general linear or linearised dynamics, whose communication topology contains a directed spanning tree. An observer-type consensus protocol based on the relative outputs of the neighbouring agents is adopted. The notion of consensus region is introduced, as a measure for the robustness of the protocol and as a basis for the protocol design. For neutrally stable agents, it is shown that there exists a protocol achieving consensus together with a consensus region that is the entire open right-half plane if and only if each agent is stabilisable and detectable. An algorithm is further presented for constructing such a protocol. For consensus with a prescribed convergence speed, a multi-step protocol design procedure is given, which yields an unbounded consensus region and at the same time maintains a favourable decoupling property. Finally, the consensus algorithms are extended to solve the formation control problems. View full abstract»

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  • Stability analysis of digital repetitive control systems under time-varying sampling period

    Page(s): 29 - 37
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (541 KB)  

    Repetitive control is an internal model principle-based technique for tracking periodic references and/or rejecting periodic disturbances. Digital repetitive controllers are usually designed assuming a fixed frequency for signals to be tracked/rejected, its main drawback being a dramatic performance decay when this frequency varies. A common approach to overcome this problem consists of an adaptive change of the sampling time according to the reference/disturbance period variation. Such a structural change may indeed compromise closed-loop stability. Nevertheless, no formal stability proofs are reported in the literature. This study addresses the stability analysis of a digital repetitive control system operating under time-varying sampling period. The procedure adapts the robust control approach introduced by Fujioka and Suh, which treats the time-varying parts of the system description as norm-bounded uncertainties, to the special features of digital repetitive control systems. This results in a conservatism reduction leading to an improvement in the obtained stability intervals. The proposed technique is also applicable to a more general class of systems incorporating a discrete-time dynamic controller. The article is completed with the application of the method to two standard examples in the repetitive control literature. Experimental results confirm the theoretical predictions. View full abstract»

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  • New method of fault-distribution-dependent memory-reliable controller design for discrete-time systems with stochastic input delays

    Page(s): 38 - 46
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (279 KB)  

    A new memory-reliable controller design for a class of discrete-time systems with time-varying input delays is proposed. By assuming that the actuator fault obeys a certain probabilistic distribution, a new practical actuator fault model is presented. Based on this fault model and the known past information, an augmented system with time-varying delay or non-delay, similar to switched systems, is established. By using the Lyapunov-Krasovskii approach, a sufficient condition for the existence of reliable controller is expressed by linear matrix inequalities. An illustrative example is exploited to show the effectiveness of the proposed design procedures. View full abstract»

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  • Stability of networked control systems with packet dropout: an average dwell time approach

    Page(s): 47 - 53
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (166 KB)  

    In this study, the authors discuss the modelling and control for a class of networked control systems (NCSs) with packet dropouts. In cases where there may be packet dropouts in both backward and forward channels in a communication network, the closed-loop NCSs are modelled as a discrete time switched system with four subsystems. By using the average dwell time method, sufficient conditions for the exponential stability of the closed-loop NCSs are presented, and the relation between the packet dropout rate and the stability of the closed-loop NCSs is explicitly established. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed method. View full abstract»

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  • Observer for discrete-time Lipschitz non-linear systems with delayed output

    Page(s): 54 - 62
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (289 KB)  

    This study presents an observer design method for discrete-time non-linear systems which have Lipschitz non-linearity and delayed output. The proposed observer has a chained form that allows us to estimate a system state sequentially from delayed output measurement. Based on an observer design for discrete-time systems without output delay, it is shown that the proposed observer guarantees the exponential convergence to zero of the estimation error in spite of the presence of output measurement delay. Finally, a numerical example is given to verify the effectiveness of our design approach. View full abstract»

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  • Minimum communication cost consensus in multi-agent systems with Markov chain patterns

    Page(s): 63 - 68
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (227 KB)  

    The authors study the problem of optimising the communication cost for multi-agent systems over both undirected topology and directed topology. The authors assume that the two adjacent agents exchange information with a certain probability. Necessary and sufficient conditions for multi-agent systems to achieve the mean square consensus are obtained by using the matrix and graph theories. In particular, the authors formulate a definition of the communication cost function and propose the methods to minimise the proposed cost function. Simulation examples are also given to illustrate the theoretical results. View full abstract»

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  • Fault detection and diagnosis based on parameter set estimation

    Page(s): 69 - 83
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (954 KB)  

    In this study, a fault detection and diagnosis strategy is proposed for the supervision of linearly parametrisable, time-invariant systems subject to abrupt parameter variations, relying on a variation of a set membership identification (SMI) approach. Based on the input-output measurements and the a priori knowledge of the noise bound, the SMI computes a feasible ellipsoidal and its supporting orthotopic parameter set, within which the nominal parameter vector resides. A fault is detected at the time instant when a hyperstrip generated from the measurement data and the noise bound does not intersect with the ellipsoid computed at the previous time instant, or when there is no intersection of the supporting orthotopes. The conditions under which the occurrence of a fault is detected followed by a seamless update of the ellipsoidal set are provided. In the sequel, the fault isolation procedure is accomplished through the computation of the projections of the certainty parameter sets, which contain the new nominal parameter vector. Finally, the fault diagnosis continues with the determination of the size and the type of parameter variation. Simulations studies are used to verify the efficiency of the suggested strategy for the case of multiple faults in a micro-electrostatic actuator. View full abstract»

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  • Design of balanced proportional-integral-derivative controllers based on bilevel optimisation

    Page(s): 84 - 92
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    A bilevel optimisation framework is proposed to find the proportional-integral-derivative (PID) controller with balanced performance in terms of transient response, actuator preservation and robustness. In the lower level problem, the transient performance is optimised so that the balanced controller can be designed with minimal controller output variation in the upper level problem, where the requirement on transient performance is relaxed to a pre-specified extent. The robustness of the system is guaranteed by constraints on the maximum sensitivity in both problems. The trade-off between transient performance and actuator preservation is controlled uniformly for diverse process dynamics by a single parameter, which characterises the uniformness of relaxation in transient performance. By choosing different values of this parameter, tuning rules are provided for first order plus time delay (FOPTD) processes for set point following and load disturbance rejection, respectively. The efficiency of these tuning rules is demonstrated by examples covering the whole plant family set. View full abstract»

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  • Back-stepping sliding mode control for missile systems based on an extended state observer

    Page(s): 93 - 102
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    A novel approach combining the sliding mode control and extended state observer (ESO) is proposed for attitude control of a missile model which is non-linear in aerodynamics. Combining the back-stepping technique, the corresponding sliding mode controller is designed to guarantee the state variables of the closed-loop system to converge to the reference state with the help of the ESO by estimating the unknown variable. Also, simulation results are presented to illustrate the effectiveness of the control strategy. View full abstract»

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  • Hybrid impulsive control for switched singular systems

    Page(s): 103 - 111
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (185 KB)  

    In this study, the authors investigate the control problem of switched singular systems aiming to compress their inconsistent state jumps when switch occurs between two different singular subsystems. The proposed hybrid impulsive controller consists of a feedback controller and an impulsive controller. With introduction of the impulsive controller, the state at each switching instant for the closed-loop system can be changed. Based on the given controller structure, some sufficient conditions are derived under which the closed-loop system is admissible (regular, impulse free and stable) and such a controller has the capability of eliminating or minimising the instantaneous state jumps at switching instants. The validity and advantage of the proposed hybrid impulsive controller are illustrated using two examples. View full abstract»

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  • Disturbance attenuation control of active suspension with non-linear actuator dynamics

    Page(s): 112 - 122
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    This study suggests an approach to design an active suspension controller with non-linear actuator dynamics, which can achieve good ride comfort while respecting safety constraints such as road holding and limited suspension strokes. The procedure includes two steps: design a state feedback & H controller for the linear subsystem with time-domain constraints, and then apply the backstepping technique to deal with non-linear actuator dynamics and to derive the control law. The closed-loop system achieves a bounded disturbance attenuation level (the l2 gain), which gives a measure of ride comfort in the case of general road disturbances. Simulation results are provided to show the effectiveness of the designed controller. View full abstract»

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  • Estimation of free flow speed and critical density in a segmented freeway using missing data and Monte Carlo-based expectation maximisation algorithm

    Page(s): 123 - 130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (467 KB)  

    This study is concerned with the estimation of two key parameters in a stochastic non-linear second-order state-space model of traffic flow using the maximum likelihood approach while employing a recursive Monte Carlo-based filtering and smoothing to solve related expectation maximisation (EM) algorithm. A maximum likelihood (ML) framework is employed in the interests of statistical efficiency. EM algorithm may be used to compute these ML estimates and Monte Carlo approach is used to compute required conditional expectations. Considered parameters, free flow speed and critical density are traffic flow characteristics which are key parameters used for traffic control, ramp metering, incident management etc. A set of field traffic data from the Interstate-494 highway located in Metro Freeway Network Area at Minnesota is used to demonstrate the effectiveness of the proposed approach. View full abstract»

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  • Hα control strategy of motor torque ripple in hybrid electric vehicles: an experimental study

    Page(s): 131 - 144
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (715 KB)  

    In this study, the authors propose a novel control strategy of torque ripple reduction in hybrid electric vehicles (HEVs). By its periodic cycle of power production, the internal combustion engine used in a hybrid vehicle provides a torque that fluctuates constantly. This is problematic for vehicle manufacturers since this torque ripple creates uncomfortable vibrations and mechanical damage. To achieve this active control, the problem is reformulated in complex notation in the frequency domain with respect to the main order of the fluctuations. A permanent magnet synchronous machine is mounted on the crankshaft in order to generate a torque sequence opposing ripple torque. The control strategy is based on a static output feedback synthesis under & H performance specification. A complete modelling of the hybrid propulsion from an experimental test bench is achieved. The model is performed at low speed (900 rpm). In fact, at this speed, the ripple is very restrictive. Experimental results highlight the control approach interest. View full abstract»

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  • Distributed adaptive consensus algorithm for networked Euler-Lagrange systems

    Page(s): 145 - 154
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    Most consensus protocols developed in the past are for linear-integrator systems or deterministic non-linear systems. Here, the authors study the state consensus for non-point, non-linear networked Euler-Lagrange systems with unknown parameters. Specifically, state consensus problems with both coupling time delay and switching topology are investigated. By establishing a unified architecture based on the passivity property, adaptive consensus protocols are developed. It is shown that state consensus is reachable despite the unknown parameters, and the estimation errors of these parameters converge to zero. Furthermore, by introducing the leader-follower architecture, the authors show that each agent will converge its origin. Finally, a numerical example is given to illustrate the effectiveness of the proposed algorithms. View full abstract»

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  • Unified control for Pendubot at four equilibrium points

    Page(s): 155 - 163
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (513 KB)  

    The authors consider the control of an underactuated mechanical system: Pendubot, which has four separated equilibrium points. A unified controller is proposed to stabilise the system at the four equilibrium points. Moreover, the proposed unified control can bring the underactuated link to ideal homoclinic orbits, which cannot be achieved by existing approaches. Simulation results verify the effectiveness of the proposed control. View full abstract»

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  • Time-constant robust analysis of a fractional order [proportional derivative] controller

    Page(s): 164 - 172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    This study discusses fractional order [proportional derivative] (FO[PD]) controller tuning rules for robustness motion control systems. According to the proposed method, the controller is designed simultaneously satisfying the robustness property with respect to time-constant variation and the desired phase margin criteria. In this study, the authors focus on the first-order plus time delay model with an integrator. A systematic tuning rule is developed for the FO[PD] controller. Numerical computation of the tuning formulae and the relationship between design specifications and design parameters are both discussed. For simplifying the computation and achieving online tuning, the crossover frequency has been discussed. Experimental results are included to validate the proposed tuning method. View full abstract»

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  • Observer-based fault diagnosis for a class of non-linear multiple input multiple output uncertain stochastic systems using B-spline expansions

    Page(s): 173 - 187
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    In this study, a high-gain non-linear observer-based fault diagnosis (FD) approach is proposed for a class of non-linear uncertain systems with measurable output probability density functions (PDFs). The objective of the presented FD algorithm is to use the measurable output PDFs and the input of the system to construct an exponential observer-based residual generator such that the fault can be detected and diagnosed. The main result is given in a constructive manner by developing a novel non-linear observer, without resort to any linearisation. By a coordinates transformation, the design of the proposed observer does not need to solve any kind of linear matrix inequalities and its expression is explicitly given. The exponential convergence of the errors in the presence of uncertainties is proved to guarantee the fastness of the proposed FD scheme by employing a class of quadratic Lyapunov functions. Furthermore, the bound of the estimation errors in the presence of faults is minimised by appropriately choosing the parameters of the presented observer. Finally a simulation example is given to illustrate the effectiveness of the proposed FD method. View full abstract»

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  • Multimodel-based techniques for the identification and adaptive control of delayed multi-input multi-output systems

    Page(s): 188 - 202
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (578 KB)  

    This study introduces a novel method to identify each individual delay in multi-input multi-output linear systems with unknown external delays, and then to apply an adaptive control strategy. The solution is based on a multi-model scheme consisting of a set of tentative delay models running in parallel along with a switching mechanism aimed at progressively updating them. Moreover, the time-varying tentative delays are proved to converge to the actual delays under certain persistent excitation-type conditions on the input signals. The presented approach can be regarded as an online implementation of an heuristic optimisation method known as pattern search, very uncommon in control systems applications. Finally, numerical examples showing the effectiveness of the proposed method are included, as well as the convergence proofs and stability properties of the closed loop. View full abstract»

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  • Universal predictive Kalman filter-based fault estimator and tracker for sampled-data non-linear time-varying systems

    Page(s): 203 - 220
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (698 KB)  

    The universal state-space adaptive observer-based fault diagnostics/estimator and the high performance tracker for the sampled-data non-linear slowly time-varying system with unanticipated decay factors in actuators/system states are proposed. The optimal linearisation technique is used to obtain the exact (local) linear model at each operating state for a non-linear system, so that the actuator and state fault detection and performance recovery of a sampled-data non-linear time-varying system can be accomplished. Additionally, an improved Kalman filter-based adaptive observer is proposed to achieve a better estimation-based performance recovery than the conventional one. A residual generation scheme and a mechanism for auto-tuning switched gain is also presented, so that the proposed methodology is applicable for the fault detection and diagnosis (FDD) for actuator and state faults to yield the high tracking performance recovery. For practical implementation, this study also takes advantage of the merit of digital redesign methodology to convert a theoretically well-designed analogue controller/observer with a high-gain property into its corresponding low-gain digital controller/observer without possibly losing the high tracking/estimation as well as FDD performance recovery. Examples are given to illustrate the effectiveness and performances of the provided methodology. View full abstract»

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  • Design of a sliding mode controller for decentralised multi-input systems [Brief Paper]

    Page(s): 221 - 230
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    According to the Lyapunov stability theorem, a design of the multiple-sliding surface (MSS) control scheme for a class of decentralised multi-input perturbed systems is proposed. Some adaptive mechanisms embedded in both the MSS and the robust controller are designed for each subsystem so that the perturbations and the effects of the unknown interconnections can be effectively overcome, and achieve asymptotical stability. This is also achieved without the knowledge of upper bounds of the perturbations except those of the uncertainties in the input gains. Finally, an example of controlling a multimachine is used to demonstrate the feasibility of the proposed methodology. View full abstract»

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  • Consensus control for high-order multi-agent systems [Brief Paper]

    Page(s): 231 - 238
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    In this study, the lth order (l ≥ 2) consensus problem for multi-agent systems is considered, which generalises the existing second-order consensus algorithm. A linear consensus protocol is proposed for solving such a consensus problem, which includes two parts: a feedback controller and interactions from the neighbours. A sufficient and necessary condition for consensus in high-order systems is obtained. As special cases, criteria for second- and third-order systems are given, in which the exact relationship between feedback gain and system parameters is established. Finally, numerical simulations are reported to illustrate the effectiveness of this protocol. View full abstract»

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  • Stability and absolute stability of a general 2-D non-linear FM second model [Brief Paper]

    Page(s): 239 - 246
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (179 KB)  

    This study deals with the stability and absolute stability of the general 2-D non-linear time-invariant Fornasini-Marchesini (FM) second model. At first, a Lyapunov-type stability theorem is presented to sufficiently guarantee the stability and (globally) asymptotical stability of general 2-D non-linear FM second model. Then, for the globally asymptotical stability, it is further improved to lessen the conservatism of the stability theorem. More importantly, the improved theorem can derive global stability criteria which have the form of linear matrix inequalities. Furthermore, based on the two theorems, some absolute stability criteria are obtained for 2-D FM second model with sector-bounded non-linearity. Finally, three numerical examples show the advantage of the improved stability theorem. View full abstract»

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  • Hα consensus control of a class of high-order multi-agent systems

    Page(s): 247 - 253
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (234 KB)  

    This study is devoted to the consensus problems for high-order multi-agent systems with external disturbances. A dynamic neighbour-based protocol is adopted for the agents with the consideration of communication time delay and external disturbances. Sufficient conditions are derived to make all agents reach consensus with H performance. Finally, simulation results are provided for demonstrating the effectiveness of the results presented. View full abstract»

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IET Control Theory & Applications is devoted to control systems in the broadest sense, covering new theoretical results and the applications of new and established control methods.

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