3,774 research outputs found
Distributed Decision Through Self-Synchronizing Sensor Networks in the Presence of Propagation Delays and Asymmetric Channels
In this paper we propose and analyze a distributed algorithm for achieving
globally optimal decisions, either estimation or detection, through a
self-synchronization mechanism among linearly coupled integrators initialized
with local measurements. We model the interaction among the nodes as a directed
graph with weights (possibly) dependent on the radio channels and we pose
special attention to the effect of the propagation delay occurring in the
exchange of data among sensors, as a function of the network geometry. We
derive necessary and sufficient conditions for the proposed system to reach a
consensus on globally optimal decision statistics. One of the major results
proved in this work is that a consensus is reached with exponential convergence
speed for any bounded delay condition if and only if the directed graph is
quasi-strongly connected. We provide a closed form expression for the global
consensus, showing that the effect of delays is, in general, the introduction
of a bias in the final decision. Finally, we exploit our closed form expression
to devise a double-step consensus mechanism able to provide an unbiased
estimate with minimum extra complexity, without the need to know or estimate
the channel parameters.Comment: To be published on IEEE Transactions on Signal Processin
Systems Structure and Control
The title of the book System, Structure and Control encompasses broad field of theory and applications of many different control approaches applied on different classes of dynamic systems. Output and state feedback control include among others robust control, optimal control or intelligent control methods such as fuzzy or neural network approach, dynamic systems are e.g. linear or nonlinear with or without time delay, fixed or uncertain, onedimensional or multidimensional. The applications cover all branches of human activities including any kind of industry, economics, biology, social sciences etc
On norm-based estimations for domains of attraction in nonlinear time-delay systems
For nonlinear time-delay systems, domains of attraction are rarely studied despite their importance for technological applications. The present paper provides methodological hints for the determination of an upper bound on the radius of attraction by numerical means. Thereby, the respective Banach space for initial functions has to be selected and primary initial functions have to be chosen. The latter are used in time-forward simulations to determine a first upper bound on the radius of attraction. Thereafter, this upper bound is refined by secondary initial functions, which result a posteriori from the preceding simulations. Additionally, a bifurcation analysis should be undertaken. This analysis results in a possible improvement of the previous estimation. An example of a time-delayed swing equation demonstrates the various aspects
Robust Control
The need to be tolerant to changes in the control systems or in the operational environment of systems subject to unknown disturbances has generated new control methods that are able to deal with the non-parametrized disturbances of systems, without adapting itself to the system uncertainty but rather providing stability in the presence of errors bound in a model. With this approach in mind and with the intention to exemplify robust control applications, this book includes selected chapters that describe models of H-infinity loop, robust stability and uncertainty, among others. Each robust control method and model discussed in this book is illustrated by a relevant example that serves as an overview of the theoretical and practical method in robust control
Dynamic Programming and Time-Varying Delay Systems
This thesis is divided into two separate parts. The first part is about Dynamic Programming for non-trivial optimal control problems. The second part introduces some useful tools for analysis of stability and performance of systems with time-varying delays. The two papers presented in the first part attacks optimal control problems with finite but rapidly increasing search space. In the first paper we try it reduce the complexity of the optimization by exploiting the structure of a certain problem. The result, if found, is an optimal solution. The second paper introduces a new general approach of relaxing the optimality constraint. The main contribution of the paper is an extension of the Bellman equality to a double inequality. This inequality is a sufficient condition for a suboptimal solution to be within a certain distance to the optimal solution. The main approach of solving the inequality in the paper is value iteration, which is shown to work well in many different applications. In the second part of the thesis, two analysis methods for systems with time-varying delays are presented in two papers. The first paper presents a set of simple graphical stability (and performance) criteria when the delays are bounded but otherwise unknown. All that is needed to verify stability is a Bode diagram of the closed loop system. For more exact computations, the last paper presents a toolbox for Matlab called Jitterbug. It calculates quadratic costs and power spectral densities of interconnected continuous-time and discrete-time linear systems. The main contribution of the toolbox is to make well known theory easily applicable for analysis of real-time systems
Contributions to Control of Electronic Power Converters
This thesis deals with the control of electronic power converters. In its development
two main parts have been differentiated. On the one hand, the problem of the voltage
balance in the capacitors of the dc-link in a three-level NPC converter is addressed. On
the other hand, given that the techniques used in the first part to model the converters
need to make certain assumptions and, with the intention of avoiding averaged models, in
the second part, switched affine models have been developed to design the control of the
output voltage in DC-DC boost type converters.
In this way, in the first part several control laws have been developed using an averaged
model formulated by duty cycles for each level in each phase. This formulation allows
to consider, in the controllers design stage, the degree of freedom associated with the
homopolar voltage injection. Therefore, the controllers are designed as well as a part of
the modulation, so that control and modulation are integrated in the same stage. In this
way, three controllers have been designed where, apart from the objective of the voltage
balance of the capacitors, other objectives such as the number of commutations or the
quality of the output signal have also been improved.
In the second part of the thesis, four methods have been developed for the design of
control laws taking advantage of the modeling of converters as switched affine systems
given their hybrid behaviour. Thus, the first two laws take advantage of this modeling using
the delta operator to avoid numerical problems when using systems where the sampling
time is very low. The first of these controllers is based on Lyapunov’s function while the
second is independent of this function, thus obtaining less conservative results.
The other two laws developed for switched affine systems use an alternative model to
that performed in the first two controllers, so certain existing disadvantages are avoided
using again a design not based on Lyapunov’s function. Thus, the first law presents a basic control but, even so, improves the results of other existing laws in the literature. Finally, a design method to deal with systems with variations in their parameters has been presented.La presente tesis trata sobre el control de convertidores electrónicos de potencia. En su
desarrollo se han diferenciado dos partes principales. Por un lado, se trata el problema
del balance de tensiones en los condensadores que forman el dc-link en un convertidor
NPC de tres niveles. Por otro lado, dado que las técnicas utilizadas en la primera parte
para modelar los convertidores necesitan realizar determinadas suposiciones y, con la
intención de evitar modelos promediados, en la segunda parte se han desarrollado
modelos afines conmutados para diseñar el control de la tensión de salida en
convertidores DC-DC tipo boost.
De esta forma, en la primera parte se han desarrollado varias leyes de control utilizando
un modelo promediado formulado mediante ciclos de trabajo para cada nivel en cada
fase. Esta formulación permite considerar en la fase de diseño de los controladores, un
grado de libertad asociado a la inyección de tensión homopolar. Por lo tanto, se diseñan
los controladores a la vez que una parte de la modulación, de forma que se integra
control y modulación en una misma fase. De esta forma, se han diseñado tres
controladores donde, a parte del objetivo de balancear la tensión de los condensadores,
se ha ido buscando mejorar también otros objetivos como el número de conmutaciones
o la calidad de la señal de salida.
En la segunda parte de la tesis, se han desarrollado cuatro leyes de control
aprovechando el modelado de convertidores como sistemas afines conmutados dada su
naturaleza híbrida. De esta forma, las dos primeras leyes, aprovechan dicho modelado
usando el operador delta para evitar problemas numéricos al utilizar sistemas donde el
tiempo de muestreo es muy bajo. El primero de dichos controladores está basado en la
función de Lyapunov mientras que el segundo es independiente de dicha función
obteniendo así resultados menos conservadores.
Las otras dos leyes desarrolladas para sistemas afines conmutados utilizan un modelado
alternativo al realizado en las dos primeras, de forma que se evitan ciertas desventajas
existentes y mantienen un diseño no basado en la función de Lyapunov. Así, la primera
ley presenta un control más básico pero que, aun así, mejora los resultados de otras
leyes existentes en la literatura. Por último, se ha presentado un procedimiento de
diseño que hace frente a sistemas con variaciones en sus parámetros
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