Showing papers by "Petar V. Kokotovic published in 1988"

Feedback linearization of sampled-data systems

Abstract: It is shown that feedback linearizability of a continuous-time system can be destroyed through the introduction of the usual sample-and-hold devices. A method whereby a feedback linearizable discrete-time model can be recovered is given. >

An integral manifold approach to reduced order dynamic modeling of synchronous machines

Abstract: The concept of integral manifolds is used to create systematically improved reduced-order models of synchronous machines. The approach is illustrated through a detailed example of a single machine connected to an infinite bus. The example shows the advantages of the manifold approach and clarifies several issues regarding such models. The basic objective of the method is to include the effects of more complex models without including the additional differential equations. This is illustrated for the effects of stator transients and damper windings on the swing equation. >

Feedback linearization in the presence of uncertainties

Abstract: After a brief review of feedback linearization, several approaches to the problem of parametric uncertainty are outlined, and the adaptive approach to both SISO and MIMO plants is discussed in detail. Based on experience with adaptive control of linear plants, two parameter update laws are chosen for nonlinear plants according to their relative degrees. The simpler of the two adaptive laws is applicable to plants with relative degree one. For plants with higher relative degree the adaptive scheme is more complex, but a simple update law can still be employed in the special case when the state diffeomorphism, required for linearization, does not depend on uncertain parameters. The simpler adaptive scheme is shown to be robust with respect to unmodelled dynamics.

Adaptive Regulation of Nonlinear Systems with Unmodeled Dynamics

Abstract: Conditions are given for global stability of an adaptive control law designed for the reduced order model of a class of higher order nonlinear plants. In the presence of unmodeled dynamics. which account for the difference between the model and the plant, the regulation property is preserved in a stability region. The size of the region is estimated via a set of bounds that not only proves robustness, but also allows a comparison between adaptive and nonadaptive nonlinear controls.

Tracking and disturbance rejection in nonlinear systems: the integral manifold approach

Abstract: The authors study the tracking and disturbance rejection problem of a class of time-invariant nonlinear systems which are linear equivalent to controllable linear systems By using a nonlinear feedback control and a slowly varying integral control, the closed-loop system asymptotically tracks a reference input and rejects disturbances which are both unknown and slowly varying The integral manifold concept is used to design a nonlinear controller >

Optimal control in singularly perturbed systems: the integral manifold approach

Abstract: With the integral manifold approach, the authors prove the unique existence of a lower order optimal problem whose optimal control and optimal trajectory are the same as that of a singularly perturbed linear-quadratic optimal problem for some initial conditions. A second-order example is used to illustrate the idea. >

On a boundedness conjecture for output error adaptive algorithms

Abstract: A boundedness conjecture is presented which states that all signals within a specified adaptive system including the output error and parameter estimates remain globally bounded for all time despite any locally unstable behavior. Results suggested by computer simulations are verified by an exact analysis of a linearized periodic version of the adaptive system. >