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Online ISSN 1751-8652 Print ISSN 1751-8644

IET Control Theory & Applications

Volume 5, Issue 6, 14 April 2011

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Volume 5, Issue 6

14 April 2011

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  • Regular Papers

    • Fault and disturbance reconstruction in non-linear systems using a network of interconnected sliding mode observers
      • Author(s): R. Sharma  and  M. Aldeen
      • Source: IET Control Theory & Applications, Volume 5, Issue 6, p. 751 –763
      • DOI:  10.1049/iet-cta.2009.0592
      • Type: Article
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      • p. 751 –763 (13)
        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.
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      Stability analysis of a combined direct and variable structure adaptive control
      • Author(s): M. Stefanello  and  H.A. Gründling
      • Source: IET Control Theory & Applications, Volume 5, Issue 6, p. 764 –774
      • DOI:  10.1049/iet-cta.2010.0010
      • Type: Article
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      • p. 764 –774 (11)
        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 Boškvić (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.
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      Filter designing with finite packet losses and its application for stochastic systems
      • Author(s): Y.G. Liu  and  B.G. Xu
      • Source: IET Control Theory & Applications, Volume 5, Issue 6, p. 775 –784
      • DOI:  10.1049/iet-cta.2010.0178
      • Type: Article
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      • p. 775 –784 (10)
        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.
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      No-weight design of H2 controllers for square plants
      • Author(s): W. Zhang ; S. Gao ; D. Gu
      • Source: IET Control Theory & Applications, Volume 5, Issue 6, p. 785 –794
      • DOI:  10.1049/iet-cta.2009.0072
      • Type: Article
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      • p. 785 –794 (10)
        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.
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      Quantised feedback stabilisation of interconnected discrete-delay systems
      • Author(s): M.S. Mahmoud ; A.Y. Al-Rayyah ; Y. Xia
      • Source: IET Control Theory & Applications, Volume 5, Issue 6, p. 795 –802
      • DOI:  10.1049/iet-cta.2010.0249
      • Type: Article
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      • p. 795 –802 (8)
        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.
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      Data-driven adaptive model-based predictive control with application in wastewater systems
      • Author(s): N.A. Wahab ; R. Katebi ; J. Balderud ; M.F. Rahmat
      • Source: IET Control Theory & Applications, Volume 5, Issue 6, p. 803 –812
      • DOI:  10.1049/iet-cta.2010.0068
      • Type: Article
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      • p. 803 –812 (10)
        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.
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      Adaptive generalised predictive temperature control for air conditioning systems
      • Author(s): Y.-L. Chang  and  C.-C. Tsai
      • Source: IET Control Theory & Applications, Volume 5, Issue 6, p. 813 –822
      • DOI:  10.1049/iet-cta.2010.0085
      • Type: Article
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      • p. 813 –822 (10)
        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.
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