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Control Theory & Applications, IET

Issue 6 • Date April 14 2011

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Displaying Results 1 - 9 of 9
  • Fault and disturbance reconstruction in non-linear systems using a network of interconnected sliding mode observers

    Page(s): 751 - 763
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (473 KB)  

    A new technique for fault diagnosis and estimation of unknown inputs in a class of non-linear systems is presented in this study. The novelty of the approach is based on utilisation of a network of two interconnected sliding mode observers, the first is used for fault diagnosis and the second is used for estimation of unknown inputs. The two observers exchange information about their respective reconstructed signals online and in real time. Conditions and proofs of conversion are presented. A salient feature of the proposed approach is that the state trajectories do not leave the sliding manifold even in presence of unknown disturbances and faults. This allows for faults and unknown inputs to be reconstructed based on information retrieved from the equivalent output error injection signal. View full abstract»

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  • Stability analysis of a combined direct and variable structure adaptive control

    Page(s): 764 - 774
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    This study presents the proofs of robust stability of a direct adaptive controller with a variable structure (VS) parcel. The control law parameters are adjusted based on a method proposed by Narendra and Boškvič (1990). In this approach, two sets of parameters must be obtained. One set is used to attain the control objective which is, in this case, to track the output of a reference model as closely as possible. The other set is of VS type, which is used to improve performance and robustness. A slight modification of the adaptive law for the VS parameters with proofs of robust stability is proposed here. With this modified law, all mathematical proofs already existing in the literature for robust direct adaptive controllers can be extended to the case under study. The combined controller is applied to a single input single output linear time invariant (SISO LTI) plant with unmodelled dynamics of multiplicative and additive types. It is proven that the combined controller can arbitrarily improve the convergence of the error while keeping the system robustness, if compared to the non-combined case. Simulation results illustrate the efficiency of the proposed control strategy. View full abstract»

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  • Filter designing with finite packet losses and its application for stochastic systems

    Page(s): 775 - 784
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    Packet losses are a general problem in networked control system and wireless sensor networks (WSNs). In order to increase estimation accuracy and reliability, a filter with finite packet losses called minimum variance filter (MVF) is designed for stochastic systems. The authors develop a packet loss model, and design a novel MVF based on the orthogonal analysis approach. The proposed filters rely only on the packet arrival probability at each time instant and do not need to know whether the measurement is received at a particular time instant. However, the proposed MVF is not applicable to non-linear cases. So an extended MVF is derived for stochastic non-linear systems and applied to track a moving target in WSNs. Simulation results show that, compared to existing methods, the proposed MVFs have superior performance. View full abstract»

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  • No-weight design of H2 controllers for square plants

    Page(s): 785 - 794
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (254 KB)  

    In this study, a reduced complexity design procedure for H2 control problems of square plants is presented. First, all stabilising controllers are parameterised. Second, a modified inner-outer factorisation is defined for unstable plants and analytical formulas are developed. Third, the unique optimal controller is analytically derived by utilising the proposed parameterisation and the modified inner-outer factorisation. Finally, a simple tuning rule is developed for quantitative performance and robustness. The proposed procedure has three features: First, it is a no-weight design. The designer is not required to choose a weight. Second, this is an analytical design. The designer can directly use the developed design formulas and thus the design procedure is significantly simplified. Third, this is a quantitative design. The designer can design the controller for quantitative performance such as overshoot or stability margin. Numerical examples are given to illustrate the proposed method. View full abstract»

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  • Quantised feedback stabilisation of interconnected discrete-delay systems

    Page(s): 795 - 802
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (497 KB)  

    The authors investigate in this study the problem of designing decentralised quantised H feedback control for a class of linear interconnected discrete-time systems. The system has unknown-but-bounded couplings and interval delays. The quantiser has an arbitrary form that satisfies a quadratic inequality constraint. A linear matrix inequality (LMI)-based method using a decentralised quantised output-feedback controller is designed at the subsystem level to render the closed-loop system delay dependent asymptotically stable with guaranteed γ-level. To show the generality of the authors' approach, it is established that several cases of interest are readily derived as special cases. The authors illustrate the theoretical developments by numerical simulations. View full abstract»

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  • Data-driven adaptive model-based predictive control with application in wastewater systems

    Page(s): 803 - 812
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (501 KB)  

    This study is concerned with the development of a new data-driven adaptive model-based predictive controller (MBPC) with input constraints. The proposed methods employ subspace identification technique and a singular value decomposition (SVD)-based optimisation strategy to formulate the control algorithm and incorporate the input constraints. Both direct adaptive model-based predictive controller (DAMBPC) and indirect adaptive model-based predictive controller (IAMBPC) are considered. In DAMBPC, the direct identification of controller parameters is desired to reduce the design effort and computational load while the IAMBPC involves a two-stage process of model identification and controller design. The former method only requires a single QR decomposition for obtaining the controller parameters and uses a receding horizon approach to process input/output data for the identification. A suboptimal SVD-based optimisation technique is proposed to incorporate the input constraints. The proposed techniques are implemented and tested on a fourth order non-linear model of a wastewater system. Simulation results are presented to compare the direct and indirect adaptive methods and to demonstrate the performance of the proposed algorithms. View full abstract»

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  • Adaptive generalised predictive temperature control for air conditioning systems

    Page(s): 813 - 822
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (555 KB)  

    This study presents an adaptive stable generalised predictive control (ASGPC) for temperature control of a class of air-conditioning systems. The proposed ASGPC method is more general and practical than the approaches presented by Rossiter et al. and Kouvaritakis et al. A real-time stable generalised predictive control (GPC) control algorithm along with a recursive least-squares parameter estimator is proposed to control the rotational speed of the water chiller pump, thereby adjusting the rate of heat exchange in a refrigeration circulation system in order to achieve temperature set-point tracking. Computer simulations are conducted to verify effectiveness of the proposed control method. Through experimental results, the proposed control method is shown capable of giving satisfactory temperature set-point tracking performance and disturbance rejection capability. View full abstract»

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  • Consensus problems for linear time-invariant multi-agent systems with saturation constraints

    Page(s): 823 - 829
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    A class of networked multi-agent systems is studied in this study where each agent has an identical dynamics of a simple integrator and the topology of the connections is fixed. It is proved that, when there are saturation constraints, a general consensus protocol widely used in the literatures for this class of multi-agent systems remains valid. As an extension, a `bang-bang` type of consensus protocol is proposed to achieve the finite-time consensus, which relaxes the previous undirected connection assumption. View full abstract»

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  • Adaptive output-feedback control for trajectory tracking of electrically driven non-holonomic mobile robots

    Page(s): 830 - 838
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (335 KB)  

    In this study, the authors propose an adaptive output-feedback controller for trajectory tracking of electrically driven non-holonomic mobile robots in the presence of parametric uncertainties. A new adaptive observer using the transformation matrices is developed to estimate the unmeasured velocities of the mobile robot. By using the transformation matrices, the designed adaptive observer can deal with quadratic velocity terms caused by the Coriolis matrix in the mobile robot dynamics as well as uncertain parameters in quadratic velocity terms. Based on the designed adaptive observer, a simple tracking controller at the actuator level is induced from the dynamic surface design methodology. Using the Lyapunov stability theory, the authors prove that all errors in a closed-loop system are uniformly ultimately bounded and converge to an adjustable neighbourhood of the origin. 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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