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    Item type:Publication, Access status: without files ,
    A hybrid approach to the synthesis of simply structured robust and gain-scheduled controllers
    (Elsevier, 2011-09)
    Chughtai, Saulat S.
    ;
    Werner, Herbert
    Frequently in engineering applications, simply structured controllers are required for plants whose dynamics are either not fully known or varies with time. The problem of designing such structurally constrained controllers is known to be NP-hard. This paper presents a method for designing such controllers for both continuous-time and discrete-time uncertain or linear parameter varying (LPV) systems. The method relies on sufficient linear matrix inequalities (LMI) conditions also presented here. These LMIs are used to evaluate performance of a given controller in terms of the worst-case induced L2-norm for complete operational envelope. The strength of this LMI formulation lies in the fact that the robust performance evaluation condition is less conservative than standard results because it is based on a parameter-dependent Lypunov function and full block multipliers which allows to consider a bound on the rate of change in parameters. The LMI conditions are used in a hybrid evolutionary-LMI algorithm. The proposed algorithm employs evolutionary search to span the solution space and LMI solvers to find the worst case performance. The algorithm is independent of the controller structure, which allows to design simply structured controllers for complex systems in a systematic way. To illustrate the approach, two applications are presented: a distillation column and a spark ignition (SI) engine. For the distillation column, simple PI controllers with first order pre-filters are designed to achieve time and frequency domain control objectives in the presence of 20% input uncertainty. For the SI engine example, gain-scheduled PID controllers are designed and tuned. these examples illustrate that the proposed approach can be used to systematically design simply structured low-order controllers, while satisfying all performance requirements in terms of the worst-case induced L2-norm.
    Publicationtype: Journal Article
      17
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    Distributed control for a class of spatially interconnected discrete-time systems
    (Elsevier, 2008)
    Chughtai, Saulat S.
    ;
    Werner, Herbert
    This paper considers the analysis and synthesis of a spatially distributed controller for discrete-time spatially interconnected parameter-varying system. The system under consideration has both discrete time and space dynamics. The concept of quadratic separators (Iwasaki and Shibata, 2001), (Chughtai and Werner, 2007) has been extended to compute a measure of worst-case performance for such systems by solving an LMI problem. The use of quadratic separator allows a systematic search for a parameter dependent Lyapunov function, thus resulting in less conservative controllers. The problem of synthesizing controllers leads to a nonlinear matrix inequality, and a hybrid evolutionary-LMI approach to solving this problem, based on LMI solvers and genetic algorithms, is proposed in this paper. A design example illustrates the efficiency of the proposed method.
    Publicationtype: Conference Paper
      15
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    New dilated LMIs to synthesize controllers for a class of spatially interconnected systems
    (Elsevier, 2008)
    Chughtai, Saulat S.
    ;
    Werner, Herbert
    This paper presents sufficient conditions based on dilated LMIs to analyze and synthesize controllers that minimize the L-2-norm of the the closed-loop system for spatially varying interconnected polytopic systems. The approach presented here searches for a parameter dependent Lyapunov function (PDLF) by dilating the original LMIs. This dilation not only helps in the search for a PDLF but also introduces extra degrees of freedom which may result in further reduction of conservatism. Approaches to synthesize full-order polytopic controllers and reduced-order, reduced-structure controllers are also presented here.
    Publicationtype: Conference Paper
      23