Oumar Diene

Adaptive filtering algorithms designed using control Liapunov functions

The standard conjugate gradient (CG) method uses orthogonality of the residues to simplify the formulas for the parameters necessary for convergence. In adaptive filtering, the sample-by-sample update of the correlation matrix and the cross-correlation vector causes a loss of the residue orthogonality in a modified online algorithm, which, in turn, results in loss of convergence and an increase of the filter quadratic mean error. This letter extends a recently proposed control Liapunov function analysis of the CG method viewed as a dynamic system in the standard feedback configuration to the case of adaptive filtering.

A Petri Net Diagnoser for Discrete Event Systems Modeled by Finite State Automata

We propose in this paper a Petri net approach to online diagnosis of discrete event systems (DESs) modeled by finite state automata. The diagnosis method is based on the construction of a Petri net diagnoser (PND) which is constructed in polynomial time and requires less memory than other methods proposed in the literature. We also present methods for the conversion of the PND to both sequential function chart and ladder diagram for implementation on a programmable logic controller (PLC). Implementation issues are also addressed in the paper.

Conjugate gradient and steepest descent constant modulus algorithms applied to a blind adaptive array

Multi-user mobile communication systems use adaptive and linearly constrained adaptive filters for blind and non-blind adaptive interference cancelation, multipath reduction, equalization, and adaptive beamforming. A conjugate gradient and a steepest descent method for real-time processing are proposed and applied to blind adaptive array processor. Simulations show that the proposed algorithms have performance comparable to those of algorithms proposed earlier.

Analysis and verification of the diagnosability of Hybrid Systems

The diagnosability analysis proposed for Discrete Event Systems (DES) can be extended to Hybrid Systems (HS) which are systems with combined discrete and continuous behavior. In this paper, an approach for the diagnosability analysis of hybrid systems is proposed, based on the combination of the diagnosability of the underlying DES and the distinguishability of the continuous modes of the HS. The main idea is to build an observer of the underlying DES enriched with new events associated to the distinguishability of the continuous variables. A definition of diagnosability of HS and a method to verify if a HS is diagnosable, using a hybrid diagnoser called clustered diagnoser, are also introduced.

Analysis of Noncharacteristic Harmonics Generated by Voltage-Source Converters Operating Under Unbalanced Voltage

This paper deals with an analytical model to evaluate the noncharacteristic harmonics that are generated by three-phase three-wire voltage-source converters (VSCs) operating under unbalanced sinusoidal voltage conditions. This model permits the calculation of the oscillating current on the VSC dc side by considering the unbalanced voltages on its ac side. It can be used to prove that the use of dc voltage control techniques to eliminate VSC dc-side double frequency voltage ripple necessarily creates three-phase currents with undesirable low-frequency harmonic components on the VSC ac side. In this paper, the attention is directed to the instantaneous oscillating real power component at twice the line frequency, rather than to other power components. The noncharacteristic current components analyzed in this paper, such as the fundamental negative sequence and third-order harmonic components of positive and negative sequences are calculated using the proposed model in time-domain simulations. A simple model to calculate the dc-side capacitor to mitigate these noncharacteristic harmonic problems is presented.

A Study of the Robustness of Iterative Methods for Linear Systems

Numerical methods are implemented in digital computers using finite precision arithmetics, in which real/complex numbers are represented by finite length words. This representation results in truncating/rounding off the numbers, which leads to numerical errors in the algorithms. The numerical errors can result in the loss of some properties of the numerical methods (for example, the orthogonality of the residues of the conjugate gradient), which, in turn, cause numerical instability. In this paper, a new model of the perturbations resulting from the use of finite precision arithmetic is proposed, based on a combination of the floating point model with the usual model of multiplicative perturbations at the input of a plant. This control perspective, applied to the classical problem of numerical perturbations due to finite precision, allows application of the well known small gain theorem of robust control theory in order to determine measures of the robustness or numerical stability of numerical algorithms.

Revisiting the maximum power transfer for linear n-ports with uncoupled loads and applications to power systems

Summary This paper revisits three classical results of circuit theory: the Thevenin theorem, the maximum power transfer theorem, and Bodes bilinear theorem, as well as its multilinear generalization due to Lin. Combining these results, it proposes a new measurement-based approach that provides a practical new version of the ‘maximum’ power transfer theorem for n-ports terminated with uncoupled loads, in the sense that it allows a functional algebraic description of the entire power hypersurface as a function of the chosen port parameters. This is more useful than merely computing port parameters for maximum power transfer, because the power hypersurface can be used along with constraints on port parameters, such as voltages, to find their values for optimal viable power transfer. An example of maximum power transfer to two chosen load buses is given for the IEEE-30 bus system, with voltage constraints, in order to show applicability to practical cases. Copyright

Non-characteristic harmonics and DC side capacitor calculation in VSC connected to a distribution system with unbalanced voltage

This paper presents a model of typical three-phase, three-wire and two-level PWM controlled voltage-source converters (VSC) suitable to investigate the non-characteristic harmonic generation at dc- and ac-side of the converter under sinusoidal unbalanced voltage condition, e.g., third order current harmonic component of positive-sequence in the VSC ac-side current. The proposed model, based on instantaneous power as well as switching functions concepts, permits to evaluate the oscillating voltage that appears on the VSC dc-side. The effect of the negative-sequence voltage component is considered on the dc capacitance calculation which consequently enables to size the dc capacitor accurately in order to keep the dc voltage ripple under pre-defined limits. The model also shows the exact dc-side voltage ripple due to the VSC ac-side negative-sequence voltage component. The dc capacitor size and the non-characteristic harmonics obtained based on the proposed model are assessed using time-domain simulation in the PSCAD program.

Computational methods for diagnosability verification of hybrid systems

Modern industrial systems are real time controlled and supervised by means of automatic computer-based control systems, combining discrete and continuous behaviors, and are best modeled as hybrid systems (HS). In this paper, two methods for the verification of the diagnosability of hybrid systems are proposed. The first method is based on the construction of a diagnoser automaton, that can also be straightforwardly used for online diagnosis, and the second method is based on a verifier automaton that, although cannot be used for online diagnosis, can be constructed in polynomial time, leading to a smaller computational complexity for the verification of the diagnosability of HS than the method using diagnoser automata. The main idea of the second method is to build a verifier of the underlying discrete-event system (DES), taking into account the distinguishability of the system modes based on the continuous state models of the HS.

Computation of Minimal Diagnosis Bases of Discrete-Event Systems Using Verifiers: Method of the Ambiguous Cyclic Paths

Abstract In order to diagnose the occurrence of a fault event of a Discrete-Event System (DES), it is first necessary to verify if the language of the system is diagnosable with respect to an observable event set and a fault event set. If the language of the system is diagnosable, then a diagnoser can be implemented. In some cases, the language of the system remains diagnosable even if some events of the observable event set become unobservable. This leads to a reduction in the number of sensors used in the diagnosis, therefore reducing the cost of the system. Another possibility is to exploit the redundancy of some sensors in order to obtain a more reliable and robust diagnosis. In this work, we propose an algorithm to find, in a systematic way, all minimal subsets of the observable event set that ensure the diagnosability of the DES (minimal diagnosis bases). The method is based on the construction of verifiers and has lower computational complexity than another method recently presented in the literature.