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Control Theory & Applications, IET

Issue 16 • Date November 3 2011

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Displaying Results 1 - 12 of 12
  • Observer design for non-linear systems based on a generalised Lipschitz condition

    Page(s): 1813 - 1818
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (187 KB)  

    The stability-sufficient condition in designing an observer for non-linear Lipschitz systems is extended such that it does not neglect the structure of given non-linearity and can be less conservative in applying to many non-linear systems. A design procedure based on full control problem is then presented to satisfy the extended condition by means of a constant observer gain. Finally, simulation examples are given to exhibit the effectiveness of the proposed condition and design procedure in dealing with some large Lipschitz non-linearities. View full abstract»

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  • Performance-oriented adaptive neural augmentation of an existing flight control system

    Page(s): 1819 - 1828
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (545 KB)  

    Control systems for safety-critical applications, including the ones relying on adaptive elements, have to be certified against strict performance and safety requirements. This study presents a practical approach for the design of a neuro-adaptive element with the specific purpose of safely recovering the performance of a reference model in presence of bounded uncertainties. The boundedness of the tracking error vector within an a-priori specified compact domain is enforced by applying robust invariant set analysis to the uncertain linear plant where the adaptive neural contribution is considered as an amplitude-bounded persistent disturbance. In this framework, tracking error requirements are specified via a set of LMI constraints and maximal allowed amplitudes for the adaptive control are computed using a numerical LMI solver. A specific neural network on-line learning and output confinement algorithm is also proposed to keep the adaptive control within selected amplitudes; as a result, the overall closed loop system has a guaranteed worst-case transient response. The proposed approach has been successfully applied to the design of a multi input multi output (MIMO) augmentation adaptive element that improves the performance of a pre-existing tracking controller for a research aircraft model. View full abstract»

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  • Spectrum-based stability analysis and stabilisation of systems described by delay differential algebraic equations

    Page(s): 1829 - 1842
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    An eigenvalue-based framework is developed for the stability analysis and stabilisation of coupled systems with time-delays, which are naturally described by delay differential algebraic equations. The spectral properties of these equations are analysed and a numerical method for computing characteristic roots and stability assessment is presented, thereby taking into account the effect of small delay perturbations on stability. Subsequently, the design of stabilising controllers with a prescribed structure or order is addressed, based on a direct optimisation approach. The effectiveness of the approach is illustrated with numerical examples. All algorithms have been implemented in publicly available software. View full abstract»

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  • Stabilising slow-switching laws for switched discrete-time linear systems

    Page(s): 1843 - 1858
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1111 KB)  

    For a class of switched discrete-time linear systems, a state-dependent switching law with dwell time is designed to make the overall system asymptotically stable. A main feature is that the Lyapunov-like function may not be monotonically decreasing in both time-driven and state-driven periods, and this feature allows the proposed stabilising switching law being of lower switching frequency in contrast with recent results. An illustrative example is employed to show the effectiveness of the proposed switching law. Furthermore, it is shown that the proposed switching law ensures that a bounded perturbation implies bounded states, and a convergent perturbation implies convergent states. When the system state is not available, an observer-based state-dependent switching law with dwell time is also developed. View full abstract»

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  • Adaptive actuator failure compensation with unknown control gain signs

    Page(s): 1859 - 1867
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (365 KB)  

    This study deals with the problem of adaptive control for a class of non-linear systems with parameterisable time-varying actuator failures. An adaptive output-feedback actuator failure compensation scheme is proposed based on the backstepping technique and the Nussbaum gain approach. The assumption on the control gain signs is removed. The boundedness of all the closed-loop signals and the asymptotic output tracking are guaranteed in spite of the unknown actuator failures. Finally, an example is given to show the effectiveness of the proposed design method. View full abstract»

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  • Adaptive tracking control for a class of pure-feedback non-linear systems including actuator hysteresis and dynamic uncertainties

    Page(s): 1868 - 1880
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (549 KB)  

    In this study, an adaptive neural network dynamic surface control for a class of pure-feedback non-linear systems with dynamic uncertainties and unknown hysteresis is proposed. The hysteresis is described by a saturated-type Prandtl-Ishlinskii (PI) model, which is more applicable than the traditional PI model. The main advantages of the authors scheme are that by introducing an initialising technique, the L performance of the tracking error can be achieved, the assumption on dynamic uncertainties is relaxed, the explosion of the complexity problem when the hysteresis is fused with back-stepping design can be eliminated, which together with the estimation of vector norm of unknown parameters makes the control law be simplified and the computational burden be greatly reduced. Simulation results are presented to demonstrate the efficiency of the proposed scheme. View full abstract»

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  • Consensus of heterogeneous multi-agent systems

    Page(s): 1881 - 1888
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (254 KB)  

    In this study, the consensus problem of heterogeneous multi-agent system is considered. First, the heterogeneous multi-agent system is proposed which is composed of first-order and second-order integrator agents in two aspects. Then, the consensus problem of heterogeneous multi-agent system is discussed with the linear consensus protocol and the saturated consensus protocol, respectively. By applying the graph theory and Lyapunov direct method, some sufficient conditions for consensus are established when the communication topologies are undirected connected graphs and leader-following networks. Finally, some examples are presented to illustrate the theoretical results. View full abstract»

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  • Approximate controllability of stochastic impulsive systems with control-dependent coefficients

    Page(s): 1889 - 1894
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (126 KB)  

    In this study, the authors investigate the approximate controllability of stochastic impulsive systems and stochastic impulsive neutral systems with control-dependent coefficients. Using the Schauder fixed point theorem, the authors derive some sufficient conditions in the form of inequalities for approximate controllability and obtain some useful results of the degenerated systems. By studying the control of the approximate controllability, some conditions for the complete controllability are also obtained. Finally, an example is presented to illustrate the effectiveness of the proposed results. View full abstract»

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  • Adaptive robust control for DC motors with input saturation

    Page(s): 1895 - 1905
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (715 KB)  

    The adaptive robust control (ARC) for DC motors subjected to parametric uncertainties, disturbances and input saturation is considered in this study. To achieve high performance while keeping the control authority within saturation limit, a saturated ARC scheme is proposed. In this scheme, a variable-gain saturation function is introduced for the virtual control law, so that the amplitude of the virtual control and its derivative decrease when the control input approaches to the prescribed bound. Consequently, the virtual control and its derivative will not be excessively large, which is crucial for stabilising the system with a bounded input. We prove that the proposed controller cannot only assure global stability, but also provide desirable control performance, that is, the tracking error can be steered to the neighbourhood of the origin in finite time. Moreover, asymptotic tracking can be achieved in the presence of parametric uncertainties only. Finally, simulation results illustrate the effectiveness of the proposed controller. View full abstract»

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  • Co-design strategy of networked control systems for treacherous network conditions

    Page(s): 1906 - 1915
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (573 KB)  

    This study presents a co-design strategy for networked control systems (NCS) that is effective for treacherous Internet conditions. The co-design is based on two adaptation layers, one on each side of the network, that make the scheme controller-independent. Two different designs based on anticipative control are presented for packet-based NCS. In the first (which is time-based), the controller works asynchronously, but the sensor sends the plant state periodically. The second design is event-based, as the sensor only sends packets when a certain condition is met. Stability results were derived for the time-based approach, and simulation and experimental results demonstrate the efficiency of the proposed design for very long delays and high packet-loss rates. In addition, the event-based approach showed a considerable reduction in network usage. View full abstract»

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  • Time-optimal sliding-mode control of a mobile robot in a dynamic environment

    Page(s): 1916 - 1924
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (385 KB)  

    In this study, an original strategy to control a mobile robot in a dynamic environment is presented. The strategy consists of two main elements. The first is the method for the online trajectory generation based on harmonic potential fields, capable of generating velocity and orientation references, which extends classical results on harmonic potential fields for the case of static environments to the case when the presence of a moving obstacle with unknown motion is considered. The second is the design of sliding-mode controllers capable of making the controlled variables of the robot track in a finite minimum time both the velocity and the orientation references. View full abstract»

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  • H filtering for linear continuous-time systems subject to sensor non-linearities

    Page(s): 1925 - 1937
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (325 KB)  

    In this study, the H filtering problem for linear continuous-time systems subject to sensor non-linearities is considered. First, the global H filtering is addressed by modelling the sensor non-linearities as sector non-linearities. The existence condition for an H filter is derived for such systems by using both the circle criterion theory and Popov criterion theory. In both cases, design methods for H filtering are proposed by means of linear matrix inequalities (LMIs)-based optimisation approach, which enables solutions to be found via efficient interior-point algorithms. To reduce the conservatism in the design of global H filters for linear systems with output saturation non-linearities, the local H filtering problem is considered. Local H filtering refers that the states are within some bounded set while a regional L2 gain is guaranteed. An LMI-based approach is developed to calculate parameter matrices of the local H filter. Numerical examples are given to demonstrate the usefulness of the proposed results. 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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