Design and Optimization of Power Delivery and Distribution Systems Using Evolutionary Computation Techniques

Nowadays computing platforms consist of a very large number of components that require to be supplied with diferent voltage levels and power requirements. Even a very small platform, like a handheld computer, may contain more than twenty diferent loads and voltage regulators. The power delivery designers of these systems are required to provide, in a very short time, the right power architecture that optimizes the performance, meets electrical specifications plus cost and size targets. The appropriate selection of the architecture and converters directly defines the performance of a given solution. Therefore, the designer needs to be able to evaluate a significant number of options in order to know with good certainty whether the selected solutions meet the size, energy eficiency and cost targets. The design dificulties of selecting the right solution arise due to the wide range of power conversion products provided by diferent manufacturers. These products range from discrete components (to build converters) to complete power conversion modules that employ diferent manufacturing technologies. Consequently, in most cases it is not possible to analyze all the alternatives (combinations of power architectures and converters) that can be built. The designer has to select a limited number of converters in order to simplify the analysis. In this thesis, in order to overcome the mentioned dificulties, a new design methodology for power supply systems is proposed. This methodology integrates evolutionary computation techniques in order to make possible analyzing a large number of possibilities. This exhaustive analysis helps the designer to quickly define a set of feasible solutions and select the best trade-off in performance according to each application. The proposed approach consists of two key steps, one for the automatic generation of architectures and other for the optimized selection of components. In this thesis are detailed the implementation of these two steps. The usefulness of the methodology is corroborated by contrasting the results using real problems and experiments designed to test the limits of the algorithms.

Pressure management in water distribution systems: current status, proposals, and future trends

Pressure management (PM) is commonly used in water distribution systems (WDSs). In the last decade, a strategic objective in the field has been the development of new scientific and technical methods for its implementation. However, due to a lack of systematic analysis of the results obtained in practical cases, progress has not always been reflected in practical actions. To address this problem, this paper provides a comprehensive analysis of the most innovative issues related to PM. The methodology proposed is based on a case-study comparison of qualitative concepts that involves published work from 140 sources. The results include a qualitative analysis covering four aspects: (1) the objectives yielded by PM; (2) types of regulation, including advanced control systems through electronic controllers; (3) new methods for designing districts; and (4) development of optimization models associated with PM. The evolution of the aforementioned four aspects is examined and discussed. Conclusions regarding the current status of each factor are drawn and proposals for future research outlined

Multiple Input-Output Bidirectional Solid State Transformer Based on a Series Resonant Converter

Las fuentes de alimentación de modo conmutado (SMPS en sus siglas en inglés) se utilizan ampliamente en una gran variedad de aplicaciones. La tarea más difícil para los diseñadores de SMPS consiste en lograr simultáneamente la operación del convertidor con alto rendimiento y alta densidad de energía. El tamaño y el peso de un convertidor de potencia está dominado por los componentes pasivos, ya que estos elementos son normalmente más grandes y más pesados que otros elementos en el circuito. Para una potencia de salida dada, la cantidad de energía almacenada en el convertidor que ha de ser entregada a la carga en cada ciclo de conmutación, es inversamente proporcional a la frecuencia de conmutación del convertidor. Por lo tanto, el aumento de la frecuencia de conmutación se considera un medio para lograr soluciones más compactas con los niveles de densidad de potencia más altos. La importancia de investigar en el rango de alta frecuencia de conmutación radica en todos los beneficios que se pueden lograr: además de la reducción en el tamaño de los componentes pasivos, el aumento de la frecuencia de conmutación puede mejorar significativamente prestaciones dinámicas de convertidores de potencia. Almacenamiento de energía pequeña y el período de conmutación corto conducen a una respuesta transitoria del convertidor más rápida en presencia de las variaciones de la tensión de entrada o de la carga. Las limitaciones más importantes del incremento de la frecuencia de conmutación se relacionan con mayores pérdidas del núcleo magnético convencional, así como las pérdidas de los devanados debido a los efectos pelicular y proximidad. También, un problema potencial es el aumento de los efectos de los elementos parásitos de los componentes magnéticos - inductancia de dispersión y la capacidad entre los devanados - que causan pérdidas adicionales debido a las corrientes no deseadas. Otro factor limitante supone el incremento de las pérdidas de conmutación y el aumento de la influencia de los elementos parásitos (pistas de circuitos impresos, interconexiones y empaquetado) en el comportamiento del circuito. El uso de topologías resonantes puede abordar estos problemas mediante el uso de las técnicas de conmutaciones suaves para reducir las pérdidas de conmutación incorporando los parásitos en los elementos del circuito. Sin embargo, las mejoras de rendimiento se reducen significativamente debido a las corrientes circulantes cuando el convertidor opera fuera de las condiciones de funcionamiento nominales. A medida que la tensión de entrada o la carga cambian las corrientes circulantes incrementan en comparación con aquellos en condiciones de funcionamiento nominales. Se pueden obtener muchos beneficios potenciales de la operación de convertidores resonantes a más alta frecuencia si se emplean en aplicaciones con condiciones de tensión de entrada favorables como las que se encuentran en las arquitecturas de potencia distribuidas. La regulación de la carga y en particular la regulación de la tensión de entrada reducen tanto la densidad de potencia del convertidor como el rendimiento. Debido a la relativamente constante tensión de bus que se encuentra en arquitecturas de potencia distribuidas los convertidores resonantes son adecuados para el uso en convertidores de tipo bus (transformadores cc/cc de estado sólido). En el mercado ya están disponibles productos comerciales de transformadores cc/cc de dos puertos que tienen muy alta densidad de potencia y alto rendimiento se basan en convertidor resonante serie que opera justo en la frecuencia de resonancia y en el orden de los megahercios. Sin embargo, las mejoras futuras en el rendimiento de las arquitecturas de potencia se esperan que vengan del uso de dos o más buses de distribución de baja tensión en vez de una sola. Teniendo eso en cuenta, el objetivo principal de esta tesis es aplicar el concepto del convertidor resonante serie que funciona en su punto óptimo en un nuevo transformador cc/cc bidireccional de puertos múltiples para atender las necesidades futuras de las arquitecturas de potencia. El nuevo transformador cc/cc bidireccional de puertos múltiples se basa en la topología de convertidor resonante serie y reduce a sólo uno el número de componentes magnéticos. Conmutaciones suaves de los interruptores hacen que sea posible la operación en las altas frecuencias de conmutación para alcanzar altas densidades de potencia. Los problemas posibles con respecto a inductancias parásitas se eliminan, ya que se absorben en los Resumen elementos del circuito. El convertidor se caracteriza con una muy buena regulación de la carga propia y cruzada debido a sus pequeñas impedancias de salida intrínsecas. El transformador cc/cc de puertos múltiples opera a una frecuencia de conmutación fija y sin regulación de la tensión de entrada. En esta tesis se analiza de forma teórica y en profundidad el funcionamiento y el diseño de la topología y del transformador, modelándolos en detalle para poder optimizar su diseño. Los resultados experimentales obtenidos se corresponden con gran exactitud a aquellos proporcionados por los modelos. El efecto de los elementos parásitos son críticos y afectan a diferentes aspectos del convertidor, regulación de la tensión de salida, pérdidas de conducción, regulación cruzada, etc. También se obtienen los criterios de diseño para seleccionar los valores de los condensadores de resonancia para lograr diferentes objetivos de diseño, tales como pérdidas de conducción mínimas, la eliminación de la regulación cruzada o conmutación en apagado con corriente cero en plena carga de todos los puentes secundarios. Las conmutaciones en encendido con tensión cero en todos los interruptores se consiguen ajustando el entrehierro para obtener una inductancia magnetizante finita en el transformador. Se propone, además, un cambio en los señales de disparo para conseguir que la operación con conmutaciones en apagado con corriente cero de todos los puentes secundarios sea independiente de la variación de la carga y de las tolerancias de los condensadores resonantes. La viabilidad de la topología propuesta se verifica a través una extensa tarea de simulación y el trabajo experimental. La optimización del diseño del transformador de alta frecuencia también se aborda en este trabajo, ya que es el componente más voluminoso en el convertidor. El impacto de de la duración del tiempo muerto y el tamaño del entrehierro en el rendimiento del convertidor se analizan en un ejemplo de diseño de transformador cc/cc de tres puertos y cientos de vatios de potencia. En la parte final de esta investigación se considera la implementación y el análisis de las prestaciones de un transformador cc/cc de cuatro puertos para una aplicación de muy baja tensión y de decenas de vatios de potencia, y sin requisitos de aislamiento. Abstract Recently, switch mode power supplies (SMPS) have been used in a great variety of applications. The most challenging issue for designers of SMPS is to achieve simultaneously high efficiency operation at high power density. The size and weight of a power converter is dominated by the passive components since these elements are normally larger and heavier than other elements in the circuit. If the output power is constant, the stored amount of energy in the converter which is to be delivered to the load in each switching cycle is inversely proportional to the converter’s switching frequency. Therefore, increasing the switching frequency is considered a mean to achieve more compact solutions at higher power density levels. The importance of investigation in high switching frequency range comes from all the benefits that can be achieved. Besides the reduction in size of passive components, increasing switching frequency can significantly improve dynamic performances of power converters. Small energy storage and short switching period lead to faster transient response of the converter against the input voltage and load variations. The most important limitations for pushing up the switching frequency are related to increased conventional magnetic core loss as well as the winding loss due to the skin and proximity effect. A potential problem is also increased magnetic parasitics – leakage inductance and capacitance between the windings – that cause additional loss due to unwanted currents. Higher switching loss and the increased influence of printed circuit boards, interconnections and packaging on circuit behavior is another limiting factor. Resonant power conversion can address these problems by using soft switching techniques to reduce switching loss incorporating the parasitics into the circuit elements. However the performance gains are significantly reduced due to the circulating currents when the converter operates out of the nominal operating conditions. As the input voltage or the load change the circulating currents become higher comparing to those ones at nominal operating conditions. Multiple Input-Output Many potential gains from operating resonant converters at higher switching frequency can be obtained if they are employed in applications with favorable input voltage conditions such as those found in distributed power architectures. Load and particularly input voltage regulation reduce a converter’s power density and efficiency. Due to a relatively constant bus voltage in distributed power architectures the resonant converters are suitable for bus voltage conversion (dc/dc or solid state transformation). Unregulated two port dc/dc transformer products achieving very high power density and efficiency figures are based on series resonant converter operating just at the resonant frequency and operating in the megahertz range are already available in the market. However, further efficiency improvements of power architectures are expected to come from using two or more separate low voltage distribution buses instead of a single one. The principal objective of this dissertation is to implement the concept of the series resonant converter operating at its optimum point into a novel bidirectional multiple port dc/dc transformer to address the future needs of power architectures. The new multiple port dc/dc transformer is based on a series resonant converter topology and reduces to only one the number of magnetic components. Soft switching commutations make possible high switching frequencies to be adopted and high power densities to be achieved. Possible problems regarding stray inductances are eliminated since they are absorbed into the circuit elements. The converter features very good inherent load and cross regulation due to the small output impedances. The proposed multiple port dc/dc transformer operates at fixed switching frequency without line regulation. Extensive theoretical analysis of the topology and modeling in details are provided in order to compare with the experimental results. The relationships that show how the output voltage regulation and conduction losses are affected by the circuit parasitics are derived. The methods to select the resonant capacitor values to achieve different design goals such as minimum conduction losses, elimination of cross regulation or ZCS operation at full load of all the secondary side bridges are discussed. ZVS turn-on of all the switches is achieved by relying on the finite magnetizing inductance of the Abstract transformer. A change of the driving pattern is proposed to achieve ZCS operation of all the secondary side bridges independent on load variations or resonant capacitor tolerances. The feasibility of the proposed topology is verified through extensive simulation and experimental work. The optimization of the high frequency transformer design is also addressed in this work since it is the most bulky component in the converter. The impact of dead time interval and the gap size on the overall converter efficiency is analyzed on the design example of the three port dc/dc transformer of several hundreds of watts of the output power for high voltage applications. The final part of this research considers the implementation and performance analysis of the four port dc/dc transformer in a low voltage application of tens of watts of the output power and without isolation requirements.

Evaluation of the applicability of FRA for inter-turn fault detection in stator windings

In this paper, the applicability of the FRA technique is discussed as a method for detecting inter-turn faults in stator windings. Firstly, this method is tested in an individual medium-voltage stator coil with satisfactory results. Secondly, the tests are extended to a medium-voltage induction motor stator winding, in which inter-turn faults are performed in every coil end of one phase. Results of the frequency response in case of inter-turn faults are evaluated in both cases for different fault resistance values. The experimental setup is also described for each experiment. The results of the application of this technique to the detection of inter-turn faults justify further research in optimizing this technique for preventive maintenance.

Validation of a novel approach to subjective quality evaluation of conventional and 3D broadcasted video services

Transmission errors are the main cause of degradation of the quality of real broadcasted video services. Therefore, knowing their impact on the quality of experience of the end users is a crucial issue. For instance, it would help to improve the performance of the distribution systems, and to develop monitoring tools to automatically estimate the quality perceived by the end users. In this paper we validate a subjective evaluation approach specifically designed to obtain meaningful results of the effects of degradations caused by transmission errors. This methodology has been already used in our previous works with monoscopic and stereoscopic videos. The validation is done by comparing the subjective ratings obtained for typical transmission errors with the proposed methodology and with the standard method Absolute Category Rating. The results show that the proposed approach could provide more representative evaluations of the quality of experience perceived by end users of conventional and 3D broadcasted video services.

Tratamientos avanzados de agua potable para eliminación de materia orgánica disuelta : aplicación del BAC

Los procesos de biofiltración por carbón activo biológico se han utilizado desde hace décadas, primeramente en Europa y después en Norte América, sin embargo no hay parámetros de diseño y operación específicos que se puedan utilizar de guía para la biofiltración. Además, el factor coste a la hora de elegir el carbón activo como medio de filtración impacta en el presupuesto, debido al elevado coste de inversión y de regeneración. A la hora de diseñar y operar filtros de carbón activo los requisitos que comúnmente se buscan son eliminar materia orgánica, olor, y sabor de agua. Dentro de la eliminación de materia orgánica se precisa la eliminación necesaria para evitar subproductos en la desinfección no deseados, y reducir los niveles de carbono orgánico disuelto biodegradable y asimilable a valores que consigan la bioestabilidad del agua producto, a fin de evitar recrecimiento de biofilm en las redes de distribución. El ozono se ha utilizado durante años como un oxidante previo a la biofiltración para reducir el olor, sabor, y color del agua, oxidando la materia orgánica convirtiendo los compuestos no biodegradables y lentamente biodegradables en biodegradables, consiguiendo que puedan ser posteriormente eliminados biológicamente en los filtros de carbón activo. Sin embargo la inestabilidad del ozono en el agua hace que se produzcan ácidos carboxilos, alcoholes y aldehídos, conocidos como subproductos de la desinfección. Con esta tesis se pretende dar respuesta principalmente a los siguientes objetivos: análisis de parámetros requeridos para el diseño de los filtros de carbón activo biológicos, necesidades de ozonización previa a la filtración, y comportamiento de la biofiltración en un sistema compuesto de coagulación sobre un filtro de carbón activo biológico. Los resultados obtenidos muestran que la biofiltración es un proceso que encaja perfectamente con los parámetros de diseño de plantas con filtración convencional. Aunque la capacidad de eliminación de materia orgánica se reduce a medida que el filtro se satura y entra en la fase biológica, la biodegradación en esta fase se mantienen estable y perdura a lo lago de los meses sin preocupaciones por la regeneración del carbón. Los valores de carbono orgánico disuelto biodegradable se mantienen por debajo de los marcados en la literatura existente para agua bioestable, lo que hace innecesaria la dosificación de ozono previa a la biofiltración. La adición de la coagulación con la corrección de pH sobre el carbón activo consigue una mejora en la reducción de la materia orgánica, sin afectar a la biodegradación del carbón activo, cumpliendo también con los requerimientos de turbidez a la salida de filtración. Lo que plantea importantes ventajas para el proceso. Granular activated carbon filters have been used for many years to treat and produce drinking water using the adsorption capacity of carbon, replacing it once the carbon lost its adsorption capacity and became saturated. On the other hand, biological activated carbon filters have been studied for decades, firstly in Europe and subsequently in North America, nevertheless are no generally accepted design and operational parameters documented to be used as design guidance for biofiltration. Perhaps this is because of the cost factor; to choose activated carbon as a filtration media requires a significant investment due to the high capital and regeneration costs. When activated carbon filters are typically required it is for the reduction of an organic load, removal of colour, taste and / or odour. In terms of organic matter reduction, the primary aim is to achieve as much removal as possible to reduce or avoid the introduction of disinfection by products, the required removal in biodegradable dissolved organic carbon and assimilable organic carbon to produce a biologically stable potable water which prohibits the regrowth of biofilm in the distribution systems. The ozone has historically been used as an oxidant to reduce colour, taste and odour by oxidizing the organic matter and increasing the biodegradability of the organic matter, enhancing the effectiveness of organic removal in downstream biological activated carbon filters. Unfortunately, ozone is unstable in water and reacts with organic matter producing carboxylic acids, alcohols, and aldehydes, known as disinfection by products. This thesis has the following objectives: determination of the required parameters for the design of the biological activated filters, the requirement of ozonization as a pre-treatment for the biological activated filters, and a performance assessment of biofiltration when coagulation is applied as a pretreatment for biological activated carbon filters. The results show that the process design parameters of biofiltration are compatible with those of conventional filtration. The organic matter removal reduces its effectiveness as soon as the filter is saturated and the biological stage starts, but the biodegradation continues steadily and lasts for a long period of time without the need of carbon regeneration. The removal of the biodegradable dissolved organic carbon is enough to produce a biostable water according to the values shown on the existing literature; therefore ozone is not required prior to the filtration. Furthermore, the addition of coagulant and pH control before the biological activated carbon filter achieves a additional removal of organic matter, without affecting the biodegradation that occurs in the activated carbon whilst also complying with the required turbidity removal.

Response threshold models, stochastic learning automata and ant colony optimization-based decentralized self-coordination algorithms for heterogeneous multi-tasks distribution in multi-robot systems

In recent decades, there has been an increasing interest in systems comprised of several autonomous mobile robots, and as a result, there has been a substantial amount of development in the eld of Articial Intelligence, especially in Robotics. There are several studies in the literature by some researchers from the scientic community that focus on the creation of intelligent machines and devices capable to imitate the functions and movements of living beings. Multi-Robot Systems (MRS) can often deal with tasks that are dicult, if not impossible, to be accomplished by a single robot. In the context of MRS, one of the main challenges is the need to control, coordinate and synchronize the operation of multiple robots to perform a specic task. This requires the development of new strategies and methods which allow us to obtain the desired system behavior in a formal and concise way. This PhD thesis aims to study the coordination of multi-robot systems, in particular, addresses the problem of the distribution of heterogeneous multi-tasks. The main interest in these systems is to understand how from simple rules inspired by the division of labor in social insects, a group of robots can perform tasks in an organized and coordinated way. We are mainly interested on truly distributed or decentralized solutions in which the robots themselves, autonomously and in an individual manner, select a particular task so that all tasks are optimally distributed. In general, to perform the multi-tasks distribution among a team of robots, they have to synchronize their actions and exchange information. Under this approach we can speak of multi-tasks selection instead of multi-tasks assignment, which means, that the agents or robots select the tasks instead of being assigned a task by a central controller. The key element in these algorithms is the estimation ix of the stimuli and the adaptive update of the thresholds. This means that each robot performs this estimate locally depending on the load or the number of pending tasks to be performed. In addition, it is very interesting the evaluation of the results in function in each approach, comparing the results obtained by the introducing noise in the number of pending loads, with the purpose of simulate the robot's error in estimating the real number of pending tasks. The main contribution of this thesis can be found in the approach based on self-organization and division of labor in social insects. An experimental scenario for the coordination problem among multiple robots, the robustness of the approaches and the generation of dynamic tasks have been presented and discussed. The particular issues studied are: Threshold models: It presents the experiments conducted to test the response threshold model with the objective to analyze the system performance index, for the problem of the distribution of heterogeneous multitasks in multi-robot systems; also has been introduced additive noise in the number of pending loads and has been generated dynamic tasks over time. Learning automata methods: It describes the experiments to test the learning automata-based probabilistic algorithms. The approach was tested to evaluate the system performance index with additive noise and with dynamic tasks generation for the same problem of the distribution of heterogeneous multi-tasks in multi-robot systems. Ant colony optimization: The goal of the experiments presented is to test the ant colony optimization-based deterministic algorithms, to achieve the distribution of heterogeneous multi-tasks in multi-robot systems. In the experiments performed, the system performance index is evaluated by introducing additive noise and dynamic tasks generation over time.

Study of the temperature distribution in Si nanowires under microscopic laser beam excitation

The use of laser beams as excitation sources for the characterization of semiconductor nanowires (NWs) is largely extended. Raman spectroscopy and photoluminescence (PL) are currently applied to the study of NWs. However, NWs are systems with poor thermal conductivity and poor heat dissipation, which result in unintentional heating under the excitation with a focused laser beam with microscopic size, as those usually used in microRaman and microPL experiments. On the other hand, the NWs have subwavelength diameter, which changes the optical absorption with respect to the absorption in bulk materials. Furthermore, the NW diameter is smaller than the laser beam spot, which means that the optical power absorbed by the NW depends on its position inside the laser beam spot. A detailed analysis of the interaction between a microscopic focused laser beam and semiconductor NWs is necessary for the understanding of the experiments involving laser beam excitation of NWs. We present in this work a numerical analysis of the thermal transport in Si NWs, where the heat source is the laser energy locally absorbed by the NW. This analysis takes account of the optical absorption, the thermal conductivity, the dimensions, diameter and length of the NWs, and the immersion medium. Both free standing and heat-sunk NWs are considered. Also, the temperature distribution in ensembles of NWs is discussed. This analysis intends to constitute a tool for the understanding of the thermal phenomena induced by laser beams in semiconductor NWs.

Application of self-organizing techniques for the distribution of heterogeneous multi-tasks in multi-robot systems

This paper focuses on the general problem of coordinating of multi-robot systems, more specifically, it addresses the self-election of heterogeneous and specialized tasks by autonomous robots. In this regard, it has proposed experimenting with two different techniques based chiefly on selforganization and emergence biologically inspired, by applying response threshold models as well as ant colony optimization. Under this approach it can speak of multi-tasks selection instead of multi-tasks allocation, that means, as the agents or robots select the tasks instead of being assigned a task by a central controller. The key element in these algorithms is the estimation of the stimuli and the adaptive update of the thresholds. This means that each robot performs this estimate locally depending on the load or the number of pending tasks to be performed. It has evaluated the robustness of the algorithms, perturbing the number of pending loads to simulate the robot’s error in estimating the real number of pending tasks and also the dynamic generation of loads through time. The paper ends with a critical discussion of experimental results.

Response threshold models and stochastic learning automata for self-coordination of heterogeneous multi-task distribution in multi-robot systems.

This paper focuses on the general problem of coordinating multiple robots. More specifically, it addresses the self-selection of heterogeneous specialized tasks by autonomous robots. In this paper we focus on a specifically distributed or decentralized approach as we are particularly interested in a decentralized solution where the robots themselves autonomously and in an individual manner, are responsible for selecting a particular task so that all the existing tasks are optimally distributed and executed. In this regard, we have established an experimental scenario to solve the corresponding multi-task distribution problem and we propose a solution using two different approaches by applying Response Threshold Models as well as Learning Automata-based probabilistic algorithms. We have evaluated the robustness of the algorithms, perturbing the number of pending loads to simulate the robot’s error in estimating the real number of pending tasks and also the dynamic generation of loads through time. The paper ends with a critical discussion of experimental results.

A voltage disturbances prototype for testing electrical generators connected to microgrids

The search for new energy models arises as a necessity to have a sustainable power supply. The inclusion of distributed generation sources (DG) allows to reduce the cost of facilities, increase the security of the grid or alleviate problems of congestion through the redistribution of power flows. In remote microgrids it is needed in a particular way a safe and reliable supply, which can cover the demand for a low cost; due to this, distributed generation is an alternative that is being widely introduced in these grids. But the remote microgrids are especially weak grids because of their small size, low voltage level, reduced network mesh and distribution lines with a high ratio R/X. This ratio affects the coupling between grid voltages and phase shifts, and stability becomes an issue of greater importance than in interconnected systems. To ensure the appropriate behavior of generation sources inserted in remote microgrids -and, in general, any electrical equipment-, it is essential to have devices for testing and certification. These devices must, not only faithfully reproduce disturbances occurring in remote microgrids, but also to behave against the equipment under test (EUT) as a real weak grid. This also makes the device commercially competitive. To meet these objectives and based on the aforementioned, it has been designed, built and tested a voltage disturbances generator, in order to provide a simple, versatile, full and easily scalable device to manufacturers and laboratories in the sector.