 Electrical and Electronic Engineering  Research Publications
Electrical and Electronic Engineering  Research Publications
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ItemTwo algorithms arising in analysis of polynomial modelsNesic, D (IEEE, 1998)Algorithms for testing observability and forward accessibility of discretetime polynomial systems are presented. The algorithms are based on symbolic computation packages  the Grobner basis method and QEPCAD. The observability test checks observability of general polynomial systems in finite time. Forward accessibility test is applicable to a large class of polynomial systems and also stops in finite time.

ItemOn the use of switched linear controllers for stabilizability of implicit recursive equationsNesic, D (IEEE, 19980101)Stabilizability of implicit recursive equations is investigated. These equations arise naturally in the context of output deadbeat control for systems described by NARMAX models. Due to nonuniqueness of the solutions of these equations a special kind of a constrained stabilizability problem is considered. We take a hybrid switching control approach in testing the existence of a locally stabilizing controller. A method for the design of a stabilizing switching controller is also presented.

ItemObservability for simple Wiener and simple WienerHammerstein systemsNesic, D (IEEE, 19980101)Necessary and sufficient conditions for observability are given for the class of simple WienerHammerstein systems. The obtained observability test resembles the well known result for the series connection of two linear systems but it is subtly different. Observability tests that we present are very easy to use.

ItemStability of high order polynomial dynamics and minimum phase discretetime systemsNešić, D ; Mareels, IMY (IEEE, 19970408)The definition of a minimum phase nonlinear system, as usually found in the literature, is not general enough to be used for some classes of systems. The nonlinearity may yield a variety of different behaviors that are not addressed and analyzed in the literature. We provide a constructive method to test several different minimum phase properties for classes of explicit and implicit discretetime polynomial systems. The method is based on a symbolic computation package called QEPCAD. Our results can also be interpreted as a constructive approach to stability and stabilizability of explicit and implicit discretetime polynomial systems.

ItemAn output dead beat controllability test for a class of odd polynomial systemsNešić, D ; Mareels, IMY (IEEE, 19970408)An output dead beat controllability test that stops after finitely many rational operations is presented for a class of odd polynomial systems. The test is based on the Gröbner basis method but it needs to be facilitated in general with the QEPCAD symbolic computation package. Geometric properties due to which output dead beat controllability may be lost are identified and analysed. The computational requirements are smaller when compared with the known output dead beat controllability tests.

ItemOn some triangular structures and the state deadbeat problem for polynomial systemsNesic, D ; Mareels, IMY (I E E E, 19970101)QEPCAD based controllability testing for polynomial discretetime systems is computationally very expensive and it may lead to nonterminating algorithms. We identify the structure of a large class of polynomial discretetime systems, which reduces the computational cost associated with the deadbeat controllability test and which may lead to finite time controllability tests. For this purpose we use QEPCAD and the Grobner basis method. The structure which we identify encompases several classes of systems for which deadbeat controllability tests exist.

ItemAnalysis of minimum phase properties for nonaffine nonlinear systemsNesic, D ; Skafidas, E ; Mareels, IMY ; Evans, RJ (IEEE, 19970101)A system can be termed nonminimum phase according to some definitions available in the literature and yet the same system may exhibit stable zero output constrained dynamics. We show that for nonaffine nonlinear systems there may not exist a continuous control law which would keep the output identically equal to zero and for which the zero output constrained dynamics are stable, whereas a discontinuous controller which achieves this exists. We give conditions for existence and present a method for design of discontinuous switching controllers which yield stable zero dynamics. In this sense, the results of this paper enlarge the class of nonaffine nonlinear systems that can be termed minimumphase.

ItemA simple controllability test for generalized Hammerstein modelsNesic, D (IEEE, 19970101)Simple necessary and sufficient conditions for deadbeat and complete controllability for a class of discretetime generalized Hammerstein systems are derived. Due to the mild nonlinear structure of the considered systems, only linear algebra is used in the controllability test. A similar result is then proved for continuoustime generalized Hammerstein systems.

ItemNecessary and sufficient conditions for output dead beat controllability for a class of polynomial systemsNesic, D ; Mareels, I ; Bastin, G ; Mahoney, R (I E E E, 19950101)Output dead beat control for a class of non linear discrete time systems, which are described by a single inputoutput polynomial difference equation, is considered. Necessary and sufficient conditions for the existence of output dead beat control (or output controllability in finite time) are presented. A tractable output dead beat controllability test is obtained.

ItemAveraging with respect to arbitrary closed sets: closeness of solutions for systems with disturbancesTeel, AR ; Nesic, D ; Moreau, L (IEEE, 20000101)We consider two different definitions of "average" for systems with disturbances: the "strong" and "weak" averages that were introduced in [7]. Our definitions are more general than those in [7] as we use the distance to an arbitrary closed set A instead of the Euclidean norm for states in the definitions of averages. This generalization allows us to deal with more general cases of averaging for systems with disturbances, such as partial averaging. Under appropriate conditions, the solutions of a timevarying system with disturbances are shown to converge uniformly on compact time intervals to the solutions of the system's average as the rate of change of time increases to infinity.