Η παρούσα διπλωματική εργασία πραγματεύεται τη κατασκευή μιας διάταξης αυτομάτου ελέγχου. Η διάταξη αυτή ελέγχει τη λειτουργία ηλεκτρικών κινητήρων με τη βοήθεια ηλεκτρονόμων και ενός προγραμματιζόμενου λογικού ελεγκτή. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Η εργασία περιλαμβάνει την κατασκευή δύο συστημάτων αυτομάτου ελέγχου. Το ένα βασιστηκε στις μεθοδους του κλασσικού αυτοματισμού και το άλλο σε πιο σύγχρονες μεθοδους αυτομάτου ελέγχου όπως είναι η χρήση προγραμματιζόμενου λογικού ελεγκτή Σκοπός είναι η δημιουργία μιας κατασκευής που θα χρησιμοποιηθεί για εργαστηριακούς σκοπούς και θα περιλαμβάνει όλα τα στοιχειά που συνθέτουν ένα σύγχρονο κύκλωμα αυτοματισμού. Μεσα από τη λειτουργία αυτής της διαταξης γινονται σαφή τα πλεονεκτήματα αλλά και οι διαφορές των δυο μεθόδων, δηλαδή του κλασσίκου αυτοματισμού και του προγραμματιζόμενου λογικού ελεγκτη. Η διάταξη που θα περιγράφει αποτελεί εξέλιξη της ήδη υπάρχουσας διάταξης αυτομάτου ελέγχου που βρίσκεται στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας. Ο προορισμός της κατασκευής για εκπαιδευτική χρήση έπαιξε σημαντικό ρολό στις επιλογές που έγιναν καθώς στόχος είναι η παρουσίαση βασικών στοιχείων και εννοιών του βιομηχανικού αυτοματισμού στον φοιτητή. Αρχικά παρουσιάζεται η ήδη υπάρχουσα διάταξη αυτομάτου ελέγχου που βρίσκεται στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών και γίνεται μια καταγραφή των ιδεών που οδήγησαν τη μελέτη και τον σχεδιασμό της κατασκευής που υλοποιήθηκε στα πλαίσια της παρουσας διπλωματικής εργασίας. Στη συνέχεια καταγράφονται τα στοιχεία ελέγχου που θα χρησιμοποιηθούν και αναλύεται ο τρόπος λειτουργίας των. Κατόπιν παρουσιάζονται οι διατάξεις προς έλεγχο και το μηχανικό κομμάτι της κατασκευής. Το επόμενο βήμα και αφού παρατεθεί το αναγκαίο θεωρητικό υπόβαθρο, είναι η εξαγωγή του σχεδίου του κυκλώματος αυτοματισμού και η καταγραφή του επιθυμητού τρόπου λειτουργίας των διατάξεων. Αυτό μας οδήγησε και στο τελικό στάδιο που ήταν η κατασκευή η οποία βασίστηκε στα όσα έχουν περιγραφεί Τέλος γίνεται παράθεση όλων των ηλεκτρολογικών σχεδίων, πινάκων καλωδιώσεων και το πρόγραμμα σύμφωνα με το οποίο λειτουργεί το λογισμικό του προγραμματιζόμενου λογικού ελεγκτή / The present diplomatic work is about the manufacture of provision of automatic control. This provision checks the operation of electric engines with the help of relays and programmed logical controller. This work was worked out in the Laboratory of electromechanic Transformation of Energy in the Department of Electronic and electrical Engineering of Polytechnic Faculty of University of Patras. The work includes the manufacture of two systems of automatic control. One it was based on the methods of classic automation and the other in more modern methods of automatic control such as the use of programmed logical controller

La transmisión asistida por relay o transmisión cooperativa es una nueva técnica de diversidad espacial donde aparece un elemento nuevo (un relay o un usuario cooperativo) en la tradicional transmisión punto a punto (fuente a destino). Ahora en la comunicación intervienen tres enlaces: fuente-relay, relay-destino y fuente-destino. El relay, además de asistir a la fuente en la transmisión de un mensaje, permite combatir las degradaciones que puede sufrir el canal como el shadowing y el pathloss. Aunque esta técnica está basada en el trabajo realizado en los 70 por Van der Meulen, Cover y El Gamal, ha sido en los últimos años cuando se han vuelto a considerar el uso de relays. En realidad, la transmisión asistida por un relay puede verse como un sistema virtual multi-antena (virtual MIMO) donde las antenas están distribuidas en diferentes terminales. Sin embargo, al contrario de los sistemas multi-antena y debido a la limitación de la actual tecnología radio, el relay debe trabajar en modo half-duplex, ya que no puede transmitir y recibir simultáneamente en la misma banda. Este hecho, motiva que la transmisión deba realizarse en dos fases ortogonales en función del modo del relay (recibiendo datos - relay-receive phase o transmitiendo datos - relay-transmit phase). Estas fases pueden implementarse en el dominio de la frecuencia o el tiempo.Esta tesis investiga protocolos y estrategias para la transmisión asistida por relay para mejorar la eficiencia espectral y homogeneizar el servicio para todos los usuarios en un sistema de comunicación celular. La introducción del relay en la comunicación implica la redefinición de muchas técnicas y protocolos considerados en las comunicaciones punto a punto y en los sistemas multi-antena, situados en la capa física y/o superiores.En primer lugar se presentan los achievable rates obtenidos por la transmisión asistida por relay en función del rol del relay (amplifica y retransmite o decodifica y retransmite), el tipo de transmisión (siempre transmite, incremental o selectiva), los datos transmitidos por el relay (repite los símbolos recibidos o son independientes) y el tipo del protocolo half duplex. En función de los terminales activos en cada fase de la comunicación (fuente, destino o relay), existen hasta cuatro protocolos. Otro aspecto considerado es la asignación de recursos (resource allocation) para cada fase de la comunicación, la cual puede estar fijada de antemano o puede ser ajustada dinámicamente en función de los canales de los diferentes enlaces. En el caso de que todos los coeficientes del canal se conocieran perfectamente, los terminales podrían transmitir síncronamente, mejorando la comunicación gracias a la ganancia debida a técnicas de pre-codificación por medio de los autovectores del canal (con antenas distribuidas).Además dos técnicas de transmisión asistida por relay son evaluadas cuando existen múltiples relays por destino. Ambas dependen del tipo de mensajes transmitidos a cada relay (mensajes independientes o uno común). La asignación de recursos para ambas técnicas puede verse como un problema convexo.Tres escenarios resumen diferentes tipos de transmisión asistida por relay para múltiples fuentes y un solo destino: RMAC (Relay-assisted Multiple Access Channel), UC (User Cooperation) and MARC (Multiple Access Relay Channel). Su diferencia se basa en el tipo de relay half- duplex considerado. La transmisión puede hacerse síncrona o asíncronamente. Las fuentes y los relays están limitados en potencia y el acceso de ellos en cada fase de la comunicación pude hacerse por medio de TDMA (time division multiple access), FDMA (frequency division multiple access) or SC (superposition coding multiple access). La asignación de recursos puede ser formulada como un problema convexo en algunos casos y la solución óptima puede ser encontrada. Seguidamente la transmisión asistida por relay y duplexada en tiempo es aplicada a un sistema celular centralizado basado en TDMA en el downlink. Con el objetivo de mejorar la eficiencia espectral se propone el reuso espacial de un slot temporal para las transmisiones de los relays hacia sus respectivos destinos (slot de relay), generando interferencia para todos los restantes destinos activos. Un algoritmo de control de potencia basado en la teoría de juegos es propuesto para combatir la interferencia generada. Bajo esa configuración, un algoritmo de scheduling investiga las posibles ganancias debidas al multi-user gain y mide el overhead introducido.Otra forma de tratar con la interferencia es la de controlar el rate de nuestra transmisión (rate control management). Bajo ciertas condiciones es posible modelar la función de densidad de probabilidad de la potencia interferente. En ese caso, la fuente ajusta el rate para maximizar el throughput de la comunicación. Esta solución es extendida para el caso en el que cada destino es asistido por varios relays. Las dos soluciones propuestas son capaces de proporcionar mejores resultados que la transmisión directa, a pesar de la interferencia existente en el slot de relay. Finalmente, se investiga el control dinámico del enlace para la transmisión asistida por relay con dos diferentes tipos de conocimiento sobre el canal: conocimiento estadístico (statistical knowledge of the channel state) o conocimiento del canal instantáneo (actual information about the current channel state).Estos dos tipos de conocimiento derivan en diferentes estrategias a utilizar para seleccionar la modulación y el esquema de codificación (MCS). En el primer caso, los rates seleccionados no están adaptados al canal actual, por lo que el destino puede recibir erróneamente los mensajes. Los protocolos de retransmisión de mensajes (ARQ - automatic repeat request) son los encargados de asegurarse la correcta recepción y son redefinidos para la transmisión asistida por relay.. En este trabajo, se especifica los códigos espacio-tiempo distribuidos, la codificación en al fuente y el relay y la longitud de las retransmisiones. Cuando la fuente conoce algún parámetro del canal instantáneo puede adaptar el MCS para esa realización del canal. En ese caso se investiga la predicción del error en las transmisiones asistidas por relay, y con ello es posible diseñar el MCS para que maximice la cantidad de información transmitida para una probabilidad de pérdida de paquete o que maximice el throughput. / The relay-assisted or cooperative transmission is a relatively new class of spatial diversity technique where a new element comes up in the conventional source-destination or point-to point communication: an assisting relay or cooperating user. The relay assists to the source in transmitting a message to the destination and allows dealing with the channel impairments like shadowing and pathloss. Although the seminal works were issued in the 70's by van der Meulen, Cover and El Gamal, it has been during the last years when it has re-gained more attention by the researchers. In fact, the relay-assisted transmission can be seen as a virtual MIMO (Multiple Input Multiple Output) with distributed antennas. In contrast to MIMO systems, the transmission requires the use of additional channel resources because of the limitation of the current radio technology: the relay terminal is constrained to work in half-duplex mode, which motivates that the transmission must be carried out in two orthogonal phases (relay-receive and relay-transmit phase), duplexed in time or frequency domains.This dissertation investigates protocols and strategies for the relay-assisted transmission which improve the spectral efficiency and homogenize service in the cellular communication systems. The new element present in the communication, the relay terminal, imposes a redefinition of many techniques and protocols commonly used in the point-to-point and MIMO systems, which are placed at the physical and upper layers.First, achievable rates using the relay-assisted transmission are provided which depend on the role of the relay (amplify-and-forward or decode-and-forward), the type of the transmission (persistent transmission, incremental or selective relaying), the data transmitted by the relays (repetition or unconstrained coding) and the type of half-duplex protocol. There are up to four protocol definition depending on the activity of the terminals on each phase. An additional aspect addressed is the resource allocation for each phase, that is, either it is fixed beforehand (static) or it is adjusted dynamically (dynamic) as a function of the channel quality. For the single-user relay- assisted transmission the resources can be allocated based on the channel quality of the different links. Moreover, if there is complete channel state information about all channel coefficients, source and relay can transmit synchronously enhancing the transmission thanks to the (distributed) eigenvector precoding techniques.Two relay-assisted transmission techniques are evaluated when a destination is assisted by multiple relays. Both depend on the messages intended to each assisting relay (independent or common messaging). The resource allocation for both techniques is shown to be convex. Additionally, three different scenarios illustrate the multi-user relay-assisted transmission with a single destination and different types of half-duplex relays: RMAC (Relay-assisted Multiple Access Channel), UC (User Cooperation) and MARC (Multiple Access Relay Channel). The relay-assisted transmission can be done synchronously or asynchronously. The sources and relays are power limited and access in each phase of the communication by TDMA (time division multiple access), FDMA (frequency division multiple access) or SC (superposition coding multiple access). For those scenarios the allocation of transmitted power and time resources can be formulated as a convex problem under some circumstances, evaluating the optimal solution.Afterwards, the relay-assisted transmission duplexed in time is applied to a centralized cellular system based on TDMA in the downlink. The reuse of one time slot for the transmissions done from the relays to destinations (relay slot) is proposed to improve the spectral efficiency. This solution produces interference for all the destinations active in that time slot. A power control algorithm (at the relays) based on game theory is proposed to combat the generated interference. Under that configuration a scheduler algorithm explores the multi-user gain for the relay-assisted transmission, measuring the introduced overhead.Another way of dealing with the interference is by rate control management. Under some circumstances it is possible to model the probability density function (pdf) of the interfering power. In such a case, the source can tune the transmission rate in order to maximize the throughput. This solution is extended to the case where each destination is assisted by multiple relays. In spite of the interfering power, both proposed solutions are able to provide significant gains over the direct transmission.Finally, the dynamic link control of the relay assisted transmission is investigated under two different assumptions on the knowledge about the channel: statistical knowledge of the channel state and actual information about the current channel state. Both types of knowledge lead to different transmission strategies, in terms of selecting the modulation and coding scheme (MCS). Under the first case, the transmission rates are not adapted to the current channel realization and the destination can decode wrongly the messages. The Automatic Repeat reQuest (ARQ) protocols are redefined for the relayassisted transmission to cope with these events. In this work we specify the (distributed) space-time codes, the coding at the source and relay and the length of the retransmissions. When there is actual information about the channel state the MCS can be adapted to the current channel realization. In such a case, the link error prediction for the relay-assisted transmission is investigated, and thus the MCS can be designed for maximizing the information rate for a given probability of packet loss or maximizing the throughput.

Protective relays are important parts of the power system. The protection guards valuable equipment, and protective relays play a vital role in performing the task. The relay detects fault conditions within an assigned area, opens and closes output contacts to cause the operation of other devices under its control. The relay acts to operate the appropriate circuit breakers to prevent damage to personnel and property. To ensure consistent reliability and proper operation, protective relay equipment must be evaluated and tested. The importance of the relay evaluation issue is linked to capability to test the relays and relaying systems using very accurate waveform representation of a fault event. The purpose of testing protective relays is to ensure correct operation of the relay for all possible power system conditions and disturbances. To fulfill this purpose, relay testing in varying network configurations and with different fault types is required. There are a variety of options that have different performance potentials and implementation constraints. Use of digital simulators to test protective relays has proven to be an invaluable mean to evaluate relay performance under realistic conditions. This thesis describes a new methodology that attempts to improve the existing practices in testing relays by using advanced digital simulator hardware, different software packages for network modeling, and new software tools for generating and replaying test waveforms. Various types of microprocessor relays are tested and evaluated through the set of scenarios. New methodology that combines different software packages to facilitate particular testing objectives is applied.

In this thesis we formulate joint cell, channel and power allocation problems within wireless communication networks. The objectives are to maximize the user with mini- mum data throughput (Shannon capacity) or to maximize the total system throughput, referred to as the max-min and max-sum problem respectively. The complexity is stud- ied together with proposed optimization- and heuristic-based approaches. In the first paper an overall joint cell, channel and power allocation max-min prob- lem is formulated. We show that the decision problem is NP-hard and that the op- timization problem is not approximable unless P is equal to NP, for instances with a sufficiently large number of channels. Further, it follows that for a feasible binary cell and channel allocation, the remaining continuous power allocation optimization problem is still not approximable unless P is equal to NP. In addition, it is shown that first-order optimality conditions give global optimum of the single channel power al- location optimization problem, although the problem is in general not convex. In the following two papers heuristics for solving the overall problem are proposed. In the second paper we consider the single channel problem with convex combinations of the max-min and the max-sum objective functions. This variable utility provides the ability of tuning the amount of fairness and total throughput. The third paper investi- gates the multiple channel setting. On a system with three cells, eight mobile users and three channels, we perform an exhaustive search over feasible cell and channel alloca- tions. The exhaustive search is then compared to the less computationally expensive heuristic approaches, presenting potential earnings to strive for. A conclusion is that several of the proposed heuristics perform very well. The final paper incorporates fixed relay stations into the overall joint cell, channel and power allocation max-min problem. The complexity is inherited from the formula- tion without relay stations. Further, we propose a heuristic channel allocation approach that shows good performance, compared to an optimization based approach, in numer- ical simulations on the relay setting. / Financial support by the Swedish Foundation for Strategic Research (SSF) QC 20110915

Thesis (M.S.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Massive multiple-input multiple-output is a promising technique for the next generation of wireless communication systems which addresses most of the critical challenges associated with concurrent relaying systems, such as digital signal processing complexity, long processing delay, and low latency wireless communications. However, the deployment of conventional fully digital beamforming methods, dedicates one radio frequency (RF) chain to each antenna, is not viable enough due to the high fabrication/implementation cost and power consumption. In this thesis, we envision to address this critical issue by reducing the number of RF chains in a viable analog/digital configuration paradigm which is usually referred to hybrid structure. From another viewpoint, the development of fifth generation enabling technologies brings new challenges to the design of power amplifiers (PAs). In particular, there is a strong demand for low-cost, nonlinear PAs which, however, introduce nonlinear distortions. On the other hand, contemporary expensive PAs show great power efficiency in their nonlinear region. Inspired by this trade-off between nonlinearity distortions and efficiency, finding an optimal operating point is highly desirable, and this is the second key contribution of this thesis.

Este trabalho apresenta um estudo de viabilidade de um Sistema de Monitoramento de Baixo Custo (SMBC), por meio da observação de ganhos operacionais no caso de serem agregadas funções de monitoramento e controle aos relés eletrônicos dos protetores (equipamentos religadores do sistema de distribuição reticulado), visando a melhoria da qualidade no fornecimento de energia elétrica através da redução dos tempos de reação das concessionárias às falhas, do aumento da vida útil dos equipamentos e redução dos custos operacionais. Um relé para protetores de rede com características apropriadas foi desenvolvido pela empresa Futura, testado nos laboratórios do IEE/USP e instalado em campo, dentro do Programa de Pesquisa e Desenvolvimento da ANEEL com a concessionária Companhia Energética de Brasília. A operação foi acompanhada por 13 meses avaliando as novas possibilidades de operação remota, os benefícios para a concessionária e os ganhos sociais. Os benefícios do uso do sistema, os ganhos operacionais, gerenciais e sociais, são relatados constatando a viabilidade técnica e econômica da adoção do sistema. Ao final, recomendações para a continuidade da pesquisa são feitas / This work presents a viability study for a Low-cost Monitoring System (SMBC), through the examination of the operational improvements on electrical network distribution systems when new functions are added to network protectors relays allowing remote monitoring and control using typical automation protocols. The improvements on energy supply quality by reducing response times to failures, extension of equipment life and pro-active actions are also evaluated. A network protector relay with the new features have been developed by Futura Automação and tested in the IEE/USP laboratories, within a Research & Development program promoted by the national electrical energy regulator, ANEEL, and the utility Companhia Energética de Brasília (CEB). The 7 new relays have been installed for field operation and for evaluation of the new possibilities of operation and possible gains for the utility took place in 13 months of continuous operation. The benefits, operational improvements, management and social gains are described assuring the technical and economical viability of the system. Recommendations for future research are made