Showing papers by "Petar V. Kokotovic published in 1992"
••
TL;DR: In this article, the emergence of robust designs for nonlinear 'interval' plants is pointed out, and some of these tools can be made adaptive and applied to nonlinear systems with unknown parameters.
Abstract: It is argued that, for a cautious design, a nonlinear analysis is needed to reveal when and why linear tools fail. Emerging nonlinear tools that can be used to overcome the limitations of nonlinear designs are discussed. It is shown that some of these tools can be made adaptive and applied to nonlinear systems with unknown parameters. The emergence of robust designs for nonlinear 'interval' plants is pointed out. >
852 citations
••
TL;DR: In this paper, a new design procedure for adaptive nonlinear control is proposed in which the number of parameter estimates is minimal, that is, equal to the unknown parameters, and the adaptive systems designed by this procedure possess stronger stability properties than those using overparametrization.
673 citations
••
TL;DR: In this paper, an approximate input-output linearization of nonlinear systems which fail to have a well defined relative degree is studied, and a method for constructing approximate systems that are input output linearizable is provided.
Abstract: Approximate input-output linearization of nonlinear systems which fail to have a well defined relative degree is studied. For such systems, a method for constructing approximate systems that are input-output linearizable is provided. The analysis presented is motivated through its application to a common undergraduate control laboratory experiment-the ball and beam-where it is shown to be more effective for trajectory tracking than the standard Jacobian linearization. >
669 citations
••
TL;DR: In this article, the authors present a set of basic tools which can be used to construct systematic procedures for nonlinear feedback design, including a backstepping procedure for observer-based global stabilization and tracking of a class of nonlinear systems.
268 citations
••
24 Jun 1992TL;DR: Model reference adaptive controllers are designed for plants with unknown dead-zones in which two sets of adjustable parameters, one belonging to a dead-zone inverse and the other to a linear controller, are kept fixed or adaptively updated.
Abstract: Model reference adaptive controllers are designed for plants with unknown dead-zones. Several control strategies are investigated in which two sets of adjustable parameters, one belonging to a dead-zone inverse and the other to a linear controller, are either kept fixed or adaptively updated. The developed adaptive control schemes ensure boundedness of all closed-loop signals and reduce the tracking error.
245 citations
••
TL;DR: In this paper, a direct model-reference adaptive control scheme for a class of single-input, single-output (SISO) nonlinear systems with unknown constant parameters is presented.
Abstract: A direct model-reference adaptive control scheme, which requires only output, rather than full-state, measurement is presented for a class of single-input, single-output (SISO) nonlinear systems with unknown constant parameters. The nonlinearities are not required to satisfy any growth conditions. The assumptions on the linear part of the nonlinear system are the same as in the standard adaptive control problem for linear systems, which appears as a special case of the nonlinear problem that is solved. >
113 citations
••
16 Dec 1992TL;DR: The backstepping procedure as discussed by the authors provides a framework for recursive designs by achieving, at each step, the strict passivity of a virtual system, in addition to boundedness, the systems designed by this procedure also possess strong convergence properties.
Abstract: A major obstacle to the wider use of the passivity concept has been its limitation to systems of relative degree one. The relative degree limitation has been effectively removed by various forms of a recursive procedure called backstepping. It is shown how backstepping is used to design a generation of adaptive controllers for nonlinear systems. The backstepping procedure provides a framework for recursive designs by achieving, at each step, the strict passivity of a virtual system. In addition to boundedness, the systems designed by this procedure also possess strong convergence properties. >
86 citations
••
TL;DR: In this paper, the authors present a backstepping procedure for designing non-dynamic feedback compensators for a class of uncertain nonlinear systems, assuming knowledge of nonlinear growth bounds on the system uncertainties, and requiring that these bounds satisfy a strict feedback condition.
72 citations
••
TL;DR: In this article, a mathematical model of backlash inverse was developed and a parametrization of the error caused by its estimate was given, and an adaptive backlash inverse controller for unknown plants with backlash was designed.
51 citations
••
24 Jun 1992TL;DR: This work presents a new set of tools for adaptive output-feedback control of nonlinear systems that interlace the design of the observer and parameter estimator with theDesign of the feedback control to avoid overparametrization and employ "nonlinear damping" terms.
Abstract: We present a new set of tools for adaptive output-feedback control of nonlinear systems. These tools interlace the design of the observer and parameter estimator with the design of the feedback control. The resulting adaptive controller avoids overparametrization and does not employ "nonlinear damping" terms.
34 citations
••
16 Dec 1992TL;DR: In this article, an approach to adaptive control of linear systems is presented, which foregoes the traditional certainty-equivalence concept, and treats the control of the linear plants with unknown parameters as a nonlinear problem.
Abstract: An approach to adaptive control of linear systems is presented. It foregoes the traditional certainty-equivalence concept, and treats the control of linear plants with unknown parameters as a nonlinear problem. The states of the resulting adaptive system converge to a manifold whose dimensions are smaller than with any previous scheme. The dynamic order of the resulting controllers is not higher (and in most cases is lower) than that of the existing adaptive schemes. A simulation comparison with a standard indirect linear scheme shows that the new nonlinear scheme achieves far superior transient performance without an increase in control effort. >
••
TL;DR: In this article, the adaptive controllers for a class of first-order linear continuous-time plants, with different estimators, and control laws, were examined, and the authors obtained explicit solutions completely describing the nonlinear behavior of the resultant adaptive systems.
Abstract: Examining adaptive controllers for a class of first-order linear continuous-time plants, with different estimators, and control laws, the authors obtain explicit solutions completely describing the nonlinear behavior of the resultant adaptive systems. Some of these adaptive systems exhibit either finite time escapes, or other forms of unbounded behavior, due to a loss of stabilizability of the estimated model. Some fixes for the loss of stabilizability problem are analyzed. Implications of these results for the general indirect adaptive/control case are discussed. >
••
01 Jan 1992TL;DR: It is demonstrated how various integrator backstepping design procedures can be combined to produce new classes of stabilizing controllers for uncertain nonlinear systems.
Abstract: We review various integrator backstepping design procedures for generating globally stabilizing controllers for uncertain nonlinear systems. By way of a case study of a simple planar system, we demonstrate how these procedures can be combined to produce new classes of stabilizing controllers. We present eight different backstepping controllers for the planar system and compare their structural properties and simulated performance.
••
TL;DR: Two new adaptive design tools are presented and it is shown how they can be used to construct systematic design procedures for non-linear systems with incomplete state information.
Abstract: Motivated by several recent adaptive non-linear control results which use either full-state or single-output feedback, we present two new adaptive design tools and show how they can be used to construct systematic design procedures for non-linear systems with incomplete state information. The main features of these procedures are illustrated on a simple third-order system. We also provide the geometric conditions which give a co-ordinate-free characterization of one of the partial-state-feedback forms to which these procedures are applicable.
••
TL;DR: In this paper, a nonlinear adaptive controller for linear plants with unknown parameters is presented. But this controller does not address the problem of linear certainty-equivalence and does not guarantee strict passivity of the adaptation loop.
••
16 Dec 1992TL;DR: In this paper, a parametrized hysteresis model and a robust adaptive law are proposed to update the controller parameters and ensure the global boundedness of the closed-loop signals.
Abstract: The authors present a parametrized hysteresis model and develop a hysteresis inverse. They then design adaptive controllers with an adaptive hysteresis inverse for plants with unknown hystereses. A novel adaptive controller structure is introduced which is capable of achieving a linear parametrization and a linear error model in the presence of a hysteresis nonlinearity. A robust adaptive law updates the controller parameters and ensures the global boundedness of the closed-loop signals. Extensive simulations show that the use of the adaptive hysteresis inverse leads to major improvements in system performance. >
••
01 Jan 1992TL;DR: In this paper, a testbed arc welding installation is used to demonstrate the practicality of the sensitivity methods in control education, beginning with the first course, and the inclusion of sensitivity methods is advocated.
Abstract: Parametric dependence of system responses is an important issue in control system analysis and design. Time domain sensitivity functions provide an efficient, simple and insightful method for evaluating parameters effects. Sensitivity function methods are reviewed, and a testbed arc welding installation is used to demonstrate the practicality of the techniques. Inclusion of sensitivity methods in control education, beginning with the first course, is advocated.