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Control Theory & Applications, IET

Issue 9 • Date June 16 2011

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Displaying Results 1 - 10 of 10
  • Improved sufficient condition for the controllability of dependent siphons in system of simple sequential processes with resources

    Page(s): 1059 - 1068
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (373 KB)  

    Ezpeleta et al. defined a class of Petri nets called system of simple sequential processes with resources, S3PR for short, which can well model some flexible manufacturing systems (FMSs) and present a deadlock prevention policy based on strict minimal siphons (SMS). However, the number of SMS grows exponentially with net size, thereby making the liveness-enforcing supervisor very complex. Li and Zhou proposed an improved policy that allows one to design a much simpler supervisor. They partitioned SMS into dependent and elementary ones, and control dependent ones by controlling elementary ones only. They give a sufficient condition to decide whether a dependent SMS is controlled by its elementary ones. However, this condition is so loose that in most cases the controllability of a dependent SMS cannot be determined although it is actually controlled. The authors propose an improved condition based on a more detailed relationship between dependent and elementary SMS. Finally, an FMS example is used to illustrate the advantage of the proposed condition. View full abstract»

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  • An improved maximally permissive deadlock prevention policy based on the theory of regions and reduction approach

    Page(s): 1069 - 1078
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    The theory of regions has been recognised as the powerful method of deadlock prevention policy for obtaining maximally permissive controllers. It is well known that all legal and live maximal behaviour of Petri net models can be preserved by using marking/transition-separation instances (MTSIs) or event-state-separation-problem (ESSP) methods. However, they encountered great difficulties in solving all sets of inequalities that is an extremely time-consuming problem. Moreover, the number of linear programming problems (LPPs) of legal markings is also exponential with net size when a plant net grows exponentially. This work proposes a novel methodology to reduce the number of MTSIs, ESSPs and LPPs. To do so, the reachability condition equations in the theory of region can be reduced under the reduction approach. The problem of LPPs can then be reduced. Additionally, crucial marking/transition-separation instances is developed in our deadlock prevention policy that allows designers to employ few MTSIs to deal with deadlocks. The advantage of the proposed policy is that a maximally permissive controller can be obtained with drastically reduced computation. Finally, experimental results infer that our proposed policy seems to be the most efficient policy among existing methods. View full abstract»

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  • Static output feedback controller design for uncertain polynomial systems: an iterative sums of squares approach

    Page(s): 1079 - 1084
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (203 KB)  

    This study examines the problem of designing a static output feedback controller for uncertain polynomial systems via an iterative sums of squares (SOS) approach. The derivation of the static output feedback controller is given in terms of the solvability conditions of state-dependent bilinear matrix inequalities (BMIs). An iterative algorithm based on the SOS decomposition is proposed to solve these state-dependent BMIs. Finally, numerical examples are provided at the end of the study as to demonstrate the validity of the proposed design technique. View full abstract»

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  • Robust H filter design for singular systems with time-varying uncertainties

    Page(s): 1085 - 1091
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (247 KB)  

    This article deals with the design of robust H<;sub>;∞<;/sub>; filter for singular systems in general form, subject to bounded time-varying uncertainties. The aim is to design linear admissible descriptor filters that ensure a guaranteed bound on the &Lscr;<;sub>;2<;/sub>; gain of the operator from the noise signals to the estimation error signal, irrespective of the time-varying uncertain parameters. A strict linear matrix inequality based method is proposed to the robust H<;sub>;∞<;/sub>; filter design employing affine Lyapunov functions. A numerical example is presented to show the efficiency of the proposed method. View full abstract»

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  • Invariant-set-based fault tolerant control using virtual sensors

    Page(s): 1092 - 1103
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (495 KB)  

    In this study an invariant-set approach to sensor FDI is employed together with control system reconfiguration based on the use of a virtual sensor. In the proposed FDI approach, invariant sets are specified for each considered healthy/faulty situation in the system's sensor structure. The detection mechanism is based on the separation between the computed invariant sets and 'transition' sets where appropriate residual variables 'jump' when faults occur. The closed-loop system is then reconfigured by means of a virtual sensor which is adapted to the detected fault. Furthermore, conditions are derived in terms of bounds on reference signals, noise and disturbances which guarantee the stability of the closed-loop system under the resulting fault tolerant control scheme for all considered fault situations. Simulation results of the proposed scheme on a longitudinal car following scenario and experimental results on a laboratory scale magnetic levitation system confirm the validity of the approach under realistic conditions. View full abstract»

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  • Switched stable control design methodology applied to vehicle rollover prevention based on switched suspension settings

    Page(s): 1104 - 1112
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    In this study a recent result on the quadratic stability of switched linear time-invariant systems is applied to the problem of vehicle rollover prevention based on selectively switching between two suspension settings. The suggested switching control scheme reduces the transient magnitude of the load transfer ratio (LTR), which is the rollover detection metric, when and if it is above a certain threshold by switching to a stiffer suspension setting from a default soft one. In this way, the controller activates only when the potential for rollover is significant as measured by the LTR. The switching suspension parameters are chosen in a way that results in closed-loop switched roll dynamic response that is guaranteed to be quadratically stable under arbitrary switching. Moreover, a spectral condition is given that allows checking the stability of the switched roll dynamics that is subject to actuator uncertainty when the upper and lower bounds of the uncertain parameters are known. Numerical simulations demonstrate the efficacy of the suggested switched control approach. View full abstract»

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  • Observability and observer design for a class of switched systems

    Page(s): 1113 - 1119
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    This study investigates the observability and observer design for a class of single output switched systems with high frequency switching, where classical observers cannot be applied directly since the high frequency switching signals are not derivable. By assuming that these signals are integrable in the less restrictive way, and defining a new output, this study shows that algebraic observer can be adopted to estimate the states of the studied switched systems. Although the main idea is explained via normal forms, it can be easily extended to treat generic switched systems with high frequency switching. View full abstract»

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  • Distributed six degree-of-freedom spacecraft formation control with possible switching topology

    Page(s): 1120 - 1130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (487 KB)  

    This work studies distributed six degree-of-freedom spacecraft formation control with possible switching topology. By rearranging the combined translational and rotational dynamics into a unified Euler-Lagrange formulation, the developed controllers can be applied directly to maintain formation as well as desired relative attitudes. Based on a novel adaptive control architecture, distributed controllers are developed, which allow for parameter uncertainties and unknown external disturbances. By using the Lyapunov theory and a non-linear switching system theory, it is proved that arbitrary desired formation and relative attitudes among spacecrafts can be obtained with either fixed or switching communication topology. Simulations are provided that demonstrate the effectiveness of our theoretical results. View full abstract»

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  • Brief paper - Adaptive discrete-time iterative learning control for non-linear multiple input multiple output systems with iteration-varying initial error and reference trajectory

    Page(s): 1131 - 1139
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (669 KB)  

    Most of the available results in iterative learning control (ILC) hitherto have considered the ILC systems with fixed initial error and iteration-invariant reference trajectory. An adaptive discrete-time ILC scheme is presented to deal with the ILC problem of non-linear multiple input multiple output systems with iteration-varying initial error and reference trajectory. The designed adaptive ILC law learns parametric system dynamics and pursues the iteration-varying reference trajectory tracking from iteration to iteration. It can drive the ILC tracking error to zero asymptotically beyond the initial time step, and keep all adjustable parameters and system signals bounded as the number of iteration approaches infinity. Numerical example is given to illustrate the effectiveness of the adaptive ILC scheme. View full abstract»

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  • Attitude control of a quadrotor aircraft subject to a class of time-varying disturbances

    Page(s): 1140 - 1146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (347 KB)  

    Here, the attitude control of a quadrotor aircraft subject to a class of disturbances is studied. Unlike disturbances mentioned in most of the existing literature, the disturbance considered here is time varying and non-vanished. An extended observer is designed to estimate the disturbance by treating it as a new unknown state. Based on the estimation, a feedback controller with a sliding mode term is designed to stabilise the attitude of the quadrotor. Furthermore, to avoid the discontinuity of the control law caused by the sliding mode term, a modified sliding mode term is designed. The resulting continuous feedback controller makes the attitude error uniformly ultimate bounded. Theoretical results are confirmed by numerical simulations. 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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