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Control Theory & Applications, IET

Issue 6 • Date June 2008

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Displaying Results 1 - 9 of 9
  • Robust tracking control for switched linear systems with time-varying delays

    Publication Year: 2008 , Page(s): 449 - 457
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (246 KB)  

    Robust tracking control for switched linear systems with time-varying delays is investigated. Sufficient conditions for the solvability of robust tracking control problem are developed. Average dwell-time approach and piecewise Lyapunov functional methods are utilised for the stability analysis and controller design, and with free weighting matrix scheme, switching control laws are obtained such that the weighted Hinfin model reference robust tracking performance is satisfied. By using linear matrix inequalities, the controller design problem can be solved efficiently. A simulation example shows the effectiveness of the proposed switching control laws. View full abstract»

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  • Trajectory tracking of cart-pendulum dynamics using multiple time-delayed feedback

    Publication Year: 2008 , Page(s): 458 - 466
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    A trajectory tracking problem is investigated for a linear time-invariant (LTI) underactuated dynamics using a fixed control law. Differently from the traditional treatment, a possible occurrence of multiple time delays in the feedback control is also considered. It is known that such time-delayed LTI systems may exhibit multiple stable operating zones (pockets) in the space of the delays. The tasks that are undertaken here are the determination of these pockets analytically, the utilisation of them for stabilisation and relevant experimental validation. The practical objective of the study is to accomplish a successful trajectory tracking for an underactuated mechanical system, cart-and-pendulum dynamics, under the presence of multiple and independent time delays. First, the authors model the system as accurately as possible, and select a desirable fixed control law for the non-delayed feedback structure. The authors then investigate the stability map corresponding to this fixed control strategy when unpreventable delays occur in the feedback. This is done using a recent methodology, which is called the cluster treatment of characteristic roots (CTCR). The authors also experimentally verify the analytical findings of CTCR and deploy a counterintuitive control strategy called the 'delay scheduling' based on the knowledge obtained from CTCR. If there is an unavoidable delay composition which renders unstable behaviour, the 'delay scheduling' suggests increasing the delays further in order to recover stability, even for underactuated systems. View full abstract»

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  • Adaptive output feedback sliding-mode manoeuvring and vibration control of flexible spacecraft with input saturation

    Publication Year: 2008 , Page(s): 467 - 478
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (615 KB)  

    A dual-stage control system design scheme for rotational manoeuvre and vibration stabilisation of a flexible spacecraft in the presence of uncertainty/external disturbances as well as control input saturation. More precisely, two separate control loops are designed. The first one uses piezoceramics as sensors and actuators to actively suppress certain flexible modes by designing modified positive position feedback compensators which add damping to flexible structures. The second is designed based on an adaptive output feedback sliding-mode control design where control input saturation is explicitly taken into consideration. The attitude controller has the ability to reject the disturbance, deal with uncertainty and to ensure that the system trajectories globally converge to the sliding mode. A modified version is designed for adapting the unknown upper bounds of the lumped perturbations as well. To study the effectiveness of the corresponding control scheme, the traditional adaptive static output feedback control case is also developed for the control system. Both analytical and numerical results are presented to show the theoretical and practical merits of this approach. View full abstract»

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  • Hierarchical adaptive interacting multiple model algorithm

    Publication Year: 2008 , Page(s): 479 - 487
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (522 KB)  

    When the interacting multiple model (IMM) algorithm is applied to the multiple model estimation problems, more models have to be used to improve the algorithm performance, but the use of too many models can degrade the algorithm performance. In view of this problem, a hierarchical adaptive IMM algorithm is presented. The centre model of each sub-model set is calculated by using the adaptive model set algorithm, of which the model set in the IMM is composed. The resulting output of the algorithm is the data fusion of the model set estimation. The Monte Carlo simulation results show that the performance of the proposed algorithm is superior to the conventional IMM with equivalent computational complexity. View full abstract»

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  • Feedback control of oxygen uptake during stimulated cycle ergometry in subjects with paraplegia

    Publication Year: 2008 , Page(s): 488 - 495
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (190 KB)  

    Regulation of exercise intensity is important for aerobic training and exercise testing. Automatic control of oxygen uptake has potential for exercise prescription and in tests to characterise cardiopulmonary status. Here, the feasibility of closed-loop control of oxygen uptake during stimulated leg-cycling exercise in paraplegia is investigated. A new control structure for this purpose is proposed, consisting of a dynamic feedback controller monitoring target and actual oxygen uptake and adjusting an exercise work rate command signal in real time. A further feedback controller automatically adjusts the stimulation intensity to achieve the commanded work rate. The approach was experimentally evaluated in a subject with paraplegia. Empirical parameter estimation results show considerable day-to-day variability in the oxygen uptake response dynamics. Feedback control tests then demonstrate that the proposed controller provided accurate tracking of the oxygen uptake command profile on separate test days, pointing to an underlying robustness of the feedback design approach against day-to-day variability in the subject's physiological response. The variance of the oxygen uptake response was considerably lower under closed-loop control than in open-loop conditions. The results of the study provide evidence for the feasibility of feedback control of oxygen uptake during stimulated cycle-ergometer exercise in paraplegic subjects. View full abstract»

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  • Discrete-time bilateral teleoperation: modelling and stability analysis

    Publication Year: 2008 , Page(s): 496 - 512
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (926 KB)  

    Discretisation of a stabilising continuous-time bilateral teleoperation controller for digital implementation may not necessarily lead to stable teleoperation. While previous research has focused on the question of passivity or stability of haptic interaction with a discretely simulated virtual wall, here the stability of master-slave teleoperation under discrete-time bilateral control is addressed. Stability regions are determined in the form of conditions involving the sampling period, control gains including the damping introduced by the controller and environment stiffness. Among the obtained stability conditions are lower and upper bounds on the controller damping in addition to upper bounds on the sampling period and the environment stiffness, implying that as the sampling period is increased, the maximum admissible stiffness of the environment with which a slave robot can stably interact is reduced. An outcome of the paper is a set of design guidelines in terms of selection of various control parameters and the sampling rate for stable teleoperation under discrete-time control. Because of the sampling period-environment stiffness tradeoff and the stability-transparency tradeoff, the obtained stability boundaries are of particular importance for hard-contact teleoperation or when the teleoperation system has near-ideal or ideal transparency. The results of the stability analysis are confirmed by a simulation study in which the bilateral controller is realised by z-domain transfer functions while the master, the slave and the environment are simulated in the s-domain. View full abstract»

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  • BIBO stabilisation of Takagi-Sugeno fuzzy systems under persistent perturbations using fuzzy output-feedback controllers

    Publication Year: 2008 , Page(s): 513 - 523
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    Fuzzy output-feedback controllers are designed to achieve a bounded input-bounded output (bibo) stabilisation of takagi-sugeno (t-s) fuzzy systems under persistent perturbations. the designed fuzzy controllers are composed of a fuzzy observer and a static state-feedback controller, both based in the parallel distributed computation method. the design is carried out minimising the induced 1-norm of the t-s system from perturbations to controlled outputs. this design can be formulated in terms of linear matrix inequalities (lmis) and bilinear matrix inequalities (bmis), which are solved using two proposed iterative lmi (ilmi) algorithms. The designed controllers assume that all the premise variables are measurable. finally, this method is applied to an example. View full abstract»

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  • Jensen integral inequality approach to stability analysis of continuous-time systems with time-varying delay

    Publication Year: 2008 , Page(s): 524 - 534
    Cited by:  Papers (21)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (190 KB)  

    The problem of stability analysis for continuous-time systems with time-varying delay is studied. By defining novel Lyapunov functionals and using the Jenson integral inequality, new delay-dependent stability conditions are obtained in terms of linear matrix inequalities. Unlike previous methods, the upper bound of the delay derivative is taken into consideration, and this upper bound is allowed to be greater than or equal to 1. It is proved that the newly proposed criteria may introduce less conservatism than some existing ones. Meanwhile, the computational complexity of the presented stability criteria is reduced greatly since fewer decision variables are involved. Numerical examples are given to illustrate the effectiveness of the proposed methods. View full abstract»

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  • Modelling and control of networked systems via jump system approach

    Publication Year: 2008 , Page(s): 535 - 541
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    The problem of data packet dropout induced by communication channel in networked control systems (NCSs) is studied in this paper. We model the NCSs with data packet dropout as jump linear systems. With a freedom matrix introduced, new equivalently sufficient conditions on the mean square stabilisation of NCSs are obtained in terms of linear matrix inequalities (LMIs). Constant stabilising state-feedback controllers can then be constructed by using the feasible solutions of some LMIs. A numerical example illustrates the effectiveness of the proposed approach. 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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