Ricardo A. Rojas

Iterative algorithm for robust performance optimization

This paper proposes an iterative algorithm for achieving robust performance optimization for uncertain linear systems. The objective is to obtain a controller which minimizes the weighted infinity norm of sensitivity for the worst uncertainty scenario. The algorithm seeks the solution to this mini-max problem by solving the associated maximal and minimal problems in an iterative sequence. The paper describes the conceptual basis of the algorithm supported by simulation examples.

Logarithmic root loci for continuous-time loops

We propose that the logarithms of closed-loop poles be drawn instead of the plain poles in root loci for continuous-time linear loops, to help visualize significant closed-loop frequency responses simultaneously at specific values of the changing open-loop parameters. We also promote the splitting of the loci into pairs of graphs showing the imaginary and real parts of the logarithms of the poles as separate functions of the changing parameters, since this allows one to foresee the effects of parameter changes on the frequency responses and, therefore, to build computational environments in which the user may steer the design of feedback control systems.<<ETX>>

Optimal Enforcement of Causality in Non-Parametric Transfer Function Estimation

Traditionally, non-parametric impulse and frequency response functions are estimated by taking the ratio of power spectral density estimates. However, this approach may often lead to non-causal estimates. In this letter, we derive a closed form expression for the impulse response estimator by smoothed empirical transfer function estimate, which allows optimal enforcement of causality on non-parametric estimators based on spectral analysis. The new method is shown to be asymptotically unbiased and of minimum covariance in a positive semidefinite sense among a broad class of linear estimators. Numerical simulations illustrate the performance of the new estimator.

PLL-based digital control with Åstrom-Hägglund tuning

Digital control based on a phase-locked loop technique is presented. The key to this control is up/down counting. A dynamical model is given which links up/down counting with integrative control. The addition of proportional-derivative or similar algorithms is suggested to improve the control performance. A variation of the Astrom-Hagglund methods is developed as a tuning procedure. Some comments are made on the sampling effects

Aportes a la Teoría y la Implementación del Método LSCR

The LSCR method (Leave-out-Sign-dominant-Correlation-Regions) provides confidence regions for the parameters of a system by evaluating a set of correlation functions calculated for the available da ...