This study takes advantage of wide area measurements to propose a centralized nonlinear controller that acts on power system stabilizers, to cooperatively increase the damping of problematic small signal oscillations all over the system. The structure based on decision trees results in a simple, efficient, and dependable methodology that imposes much less computational burden than other nonlinear design approaches, making it a promising candidate for actual implementation by utilities and system operators. Details are given to utilize existing stabilizers while causing minimum changes to the equipment, and warranting improvement or at least no detriment of current system behavior. This enables power system stabilizers to overcome their inherent limitation to act only on the basis of local measurements to damp a single target frequency. This study demonstrates the implications of this new input on mathematical models, and the control functionality that is made available by its incorporation to conventional stabilizers. In preparation of the case of study, a heuristic dynamic reduction methodology is introduced that preserves a physical equivalent model, and that can be interpreted by any commercial software package. The steps of this method are general, versatile, and of easy adaptation to any particular power system model, with the aggregated value of producing a physical model as final result, that makes the approach appealing for industry. The accuracy of the resulting reduced network has been demonstrated with the model of the Central American System. / Ph. D.

Monitoring and protection of power systems is a task that has manifold objectives. Amongst others, it involves performing data mining, optimizing available resources, assessing system stresses, and doing data conditioning. The role of PMUs in fulfilling these four objectives forms the basis of this dissertation. Classification and regression tree (CART) built using phasor data has been extensively used in power systems. The splits in CART are based on a single attribute or a combination of variables chosen by CART itself rather than the user. But as PMU data consists of complex numbers, both the attributes, should be considered simultaneously for making critical decisions. An algorithm is proposed here that expresses high dimensional, multivariate data as a single attribute in order to successfully perform splits in CART. In order to reap maximum benefits from placement of PMUs in the power grid, their locations must be selected judiciously. A gradual PMU placement scheme is developed here that ensures observability as well as protects critical parts of the system. In order to circumvent the computational burden of the optimization, this scheme is combined with a topology-based system partitioning technique to make it applicable to virtually any sized system. A power system is a dynamic being, and its health needs to be monitored at all times. Two metrics are proposed here to monitor stress of a power system in real-time. Angle difference between buses located across the network and voltage sensitivity of buses lying in the middle are found to accurately reflect the static and dynamic stress of the system. The results indicate that by setting appropriate alerts/alarm limits based on these two metrics, a more secure power system operation can be realized. A PMU-only linear state estimator is intrinsically superior to its predecessors with respect to performance and reliability. However, ensuring quality of the data stream that leaves this estimator is crucial. A methodology for performing synchrophasor data conditioning and validation that fits neatly into the existing linear state estimation formulation is developed here. The results indicate that the proposed methodology provides a computationally simple, elegant solution to the synchrophasor data quality problem. / Ph. D.

Over the last decade, power systems have evolved dramatically around the world, owing to higher demand, stringent requirements on quality and environmental concerns that are becoming increasingly critical. With the introduction of new technologies like large-scale renewable energy, wide-area measurement based on phasor measurement units (PMUs) and consumer interaction in the distribution system, the power grid today has become more potent than ever before. Most of the defining features of the smart grid today rest on the integration of advanced communication capabilities into the grid. While communication infrastructure has become a key enabler for the smart grid, it also introduces new and complex control challenges that must be addressed. As we increasingly rely on information transmitted to distant areas over communication networks, it becomes imperative to model the effects of the communication system on the stability of the power grid. Several approaches exist in control theory to study such systems, widely referred to as Networked Control Systems (NCS). Networked control theory provides mathematical tools for system stability analysis and control in the presence of communication delays, packet dropouts and disordering due to transmission of sensor and actuator signals via a limited communication network. In this thesis, a networked control framework for smart grids with integrated commu-nication infrastructure (ICT) is developed. In particular, a networked control systems perspective is developed for two scenarios - wide-area monitoring control, and coordinated control of distributed generation sources. The effects of communication delays and packet dropouts on power system stability are modeled in detail. In the wide-area monitoring control problem, system state measurements are trans-mitted from remote locations through a communication network. The system is modeled as an NCS and a control design approach is presented to damp inter-area oscillations arising from various power system disturbances in the presence of communication constraints. In the coordinated control scenario, a power system with geographically dispersed sources is modeled as an NCS. A networked controller is designed to stabilize the system in the presence of small signal disturbances when system measurements are subject to communication delays and packet dropouts. A realistic output feedback networked control scheme that only uses voltage measurements from PMUs is also developed for practical implementation. The networked controllers designed in this thesis are validated against controllers designed by standard methods, by simulation on standard test systems. The networked controllers are found to enhance power system stability and load transfer capability even in the presence of severe packet dropouts and delays. Several extensions and theoretical problems motivated by this thesis are also proposed.

[ES] Cerca de 3.000 millones de personas en todo el mundo no pueden aprovechar ni siquiera los servicios de conectividad más básicos, ya que la mayoría de ellas viven en zonas rurales o países en vías de desarrollo. Incluso los servicios de mensajería más simples serian de gran ayuda, por ejemplo, para los agricultores que desean conocer el precio de las mercancías que les interesa vender o comprar antes de decidir si se emprende un viaje posiblemente largo, caro y agotador. La tecnología LoRa permite realizar enlaces de larga distancia con un consumo reducido de energía a bajo coste, siendo su principal limitación el escaso ancho de banda que ofrece. Con LoRa, los lugares remotos, como las zonas rurales, pueden beneficiarse de servicios basados en la conectividad que, de otro modo, serían imposibles. Nuestra propuesta entra en la categoría de redes comunitarias, en las que los usuarios construyen su propia red cuando no hay infraestructura comercial disponible. Además de la simple aplicación de mensajería, LoRa puede utilizarse para distribuir información de sensores a las comunidades o para proporcionar alertas de desastres o datos meteorológicos. Presentamos un protocolo flexible basado en la tecnología LoRa que permite la transferencia de "contenido" denominado LoRaCTP, el cual proporciona los mecanismos necesarios para que LoRa sea fiable, introduciendo una configuración de conexión ligera. Hemos diseñado este protocolo también como soporte de comunicación para las soluciones IoT basadas en edge computing, dada su estabilidad, el bajo consumo de energía y la posibilidad de cubrir largas distancias. Integramos una arquitectura que permite la recolección de datos de fuentes externas genéricas. Especialmente las fuentes de audio, apuntando a dos servicios básicos: un sistema de mensajería de voz que permite a los usuarios que no saben leer o escribir, realizar notas de voz, y un servicio de compresión de audio para extraer las principales características de la entrada de audio y utilizarla para desarrollar análisis de audio inteligente basado en Machine Learning. Combinamos IoT y Edge computing en un enfoque de innovación frugal, para proponer una solución "ingeniosa", en términos de utilización mínima de recursos y sostenibilidad, para construir un soporte básico para un sistema IoT en áreas rurales. Incluimos un proxy MQTT para integrar dispositivos de bajo coste y bajo consumo en un sistema de mensajería basado en LoRa. A través de una interfaz REST, mostramos cómo se puede usar nuestra plataforma para distribuir información de sensores de las comunidades rurales. Además, MQTT permite que estos datos se proporcionen a "lagos de datos" externos para que puedan usarse para tareas tales como informes, visualización, análisis avanzado y aprendizaje automático. Describimos una arquitectura genérica de edge/fog, utilizando microservicios, un sistema basado en MQTT que puede recopilar datos de ingreso, manejar su persistencia y coordinar la integración de datos con la nube utilizando un servicio específico llamado agregador. Las estaciones edge tienen un canal dedicado con el agregador que se basa en LoRa para permitir transmisiones de largo alcance con bajo consumo de energía. / [CA] Prop de 3.000 milions de persones a tot el món no poden aprofitar ni tan sols els serveis de connectivitat més bàsics, ja que la majoria d'elles viuen en zones rurals o països en vies de desenvolupament. Fins i tot els serveis de missatgeria més simples serien de gran ajuda, per exemple, per als agricultors que desitgen conèixer el preu de les mercaderies que els interessa vendre o comprar abans de decidir si s'emprèn un viatge possiblement llarg, car i esgotador. La tecnologia LoRa permet realitzar enllaços de llarga distància amb un consum reduït d'energia a baix cost, sent la seua principal limitació l'escassa amplada de banda que ofereix. Amb LoRa, els llocs remots, com les zones rurals, poden beneficiar-se de serveis basats en la connectivitat que, d'una altra manera, serien impossibles. La nostra proposta entra en la categoria de xarxes comunitàries, en les quals els usuaris construeixen la seua pròpia xarxa quan no hi ha infraestructura comercial disponible. A més de la simple aplicació de missatgeria, LoRa pot utilitzarse per a distribuir informació de sensors a les comunitats o per a proporcionar alertes de desastres o dades meteorològiques. Presentem un protocol flexible basat en la tecnologia LoRa que permet la transferència de "contingut" denominat LoRaCTP, el qual proporciona els mecanismes necessaris perquè LoRa siga fiable, introduint una configuració de connexió lleugera. Hem dissenyat aquest protocol també com a suport de comunicació per a les solucions IoT basades en edge computing, donada la seua estabilitat, el baix consum d'energia i la possibilitat de cobrir llargues distàncies. Integrem una arquitectura que permet la recol·lecció de dades de fonts externes genèriques. Especialment, les fonts d'àudio, apuntant a dos serveis bàsics: un sistema de missatgeria de veu que permet als usuaris que no saben llegir o escriure realitzar notes de veu, i un servei de compressió d'àudio per a extraure les principals característiques de l'entrada d'àudio i utilitzar-la per a desenvolupar anàlisi d'àudio intel·ligent basat en Machine Learning. Combinem IoT i Edge computing en un enfocament d'innovació frugal, per a proposar una solució "enginyosa", en termes d'utilització mínima de recursos i sostenibilitat, per a construir un suport bàsic per a un sistema IoT en àrees rurals. Incloem un proxy MQTT per a integrar dispositius de baix cost i baix consum en un sistema de missatgeria basat en LoRa. A través d'una interfície REST, vam mostrar com es pot usar la nostra plataforma per a distribuir informació de sensors de les comunitats rurals. A més, MQTT permet que aquestes dades es proporcionen a "llacs de dades" externes perquè puguen usar-se per a tasques com ara informes, visualització, anàlisi avançada i aprenentatge automàtic. Descrivim una arquitectura genèrica de edge/fog, utilitzant microserveis, un sistema basat en MQTT que pot recopilar dades d'ingrés, manejar la seua persistència i coordinar la integració de dades amb el núvol utilitzant un servei específic anomenat agregador. Les estacions edge tenen un canal dedicat amb el agregador que es basa en LoRa per a permetre transmissions de llarg abast amb baix consum d'energia. / [EN] Nearly 3 billion people around the world are unable to take advantage of even the most basic connectivity services, as most of them live in rural areas or developing countries. Even the simplest messaging services would be of great help, for example, to farmers who want to know the price of goods they are interested in selling or buying before deciding whether to embark on a possibly long, expensive and exhausting journey. LoRa technology enables long-distance links with reduced power consumption at low cost, its main limitation being the low bandwidth it offers. With LoRa, remote locations, such as rural areas, can benefit from connectivity-based services that would otherwise be impossible. Our proposal falls into the category of community networks, where users build their own network when commercial infrastructure is not available. In addition to a simple messaging application, LoRa can be used to distribute sensor information to communities or to provide disaster alerts or weather data. We present a flexible protocol based on LoRa technology that enables the transfer of "content" called LoRaCTP, which provides the necessary mechanisms for LoRa to be reliable, introducing a lightweight connection setup. We have designed this protocol also as a communication support for IoT solutions based on edge computing, given its stability, low power consumption and the possibility of covering long distances. Likewise, we integrated an architecture that allows data collection from generic external sources. Especially audio sources, targeting two basic services: a voice messaging system that allows users who cannot read or write to make voice notes, and an audio compression service to extract the main features of the audio input and use it to develop intelligent audio analytics based on Machine Learning. We combine IoT and Edge computing in a frugal innovation approach, to propose an "ingenious" solution, in terms of minimum resource utilization and sustainability, to build a basic support for an IoT system in rural areas. We include an MQTT proxy to integrate low-cost and low-power devices into a LoRa-based messaging system. Through a REST interface, we show how our platform can be used to distribute sensor information from rural communities. In addition, MQTT allows this data to be provided to external "data lakes" so that it can be used for tasks such as reporting, visualization, advanced analytics, and machine learning. We describe a generic edge/fog architecture, using microservices, an MQTT-based system that can collect ingress data, manage its persistence, and coordinate data integration with the cloud using a specific service called an aggregator. The edge stations have a dedicated channel with the aggregator that is based on LoRa to enable long-range transmissions with low power consumption. / Agradezco al Gobierno de los Estados Unidos Mexicanos a través del Consejo Nacional de Ciencia y Tecnología (CONACYT) y al Gobierno de Chiapas mediante el Consejo de Ciencia y Tecnología del Estado de Chiapas (COCYTECH) por brindarme la oportunidad de mejoramiento profesional y académico por medio del programa de becas “CONACYT - Gobierno del Estado de Chiapas” en la convocatoria del 2017. / Nakamura Pinto, MK. (2022). Diseño de un sistema de mensajería instantánea para redes comunitarias [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/188948

Classically, wide-area synchronized power system monitoring has been an expensive task requiring significant investment in utility communications infrastructures for the service of relatively few costly sensors. The purpose of this research is to demonstrate the viability of power system monitoring from very low voltage levels (120 V). Challenging the accepted norms in power system monitoring, the document will present the use of inexpensive GPS time synchronized sensors in mass numbers at the distribution level. In the past, such low level monitoring has been overlooked due to a perceived imbalance between the required investment and the usefulness of the resulting deluge of information. However, distribution level monitoring offers several advantages over bulk transmission system monitoring. First, practically everyone with access to electricity also has a measurement port into the electric power system. Second, internet access and GPS availability have become pedestrian commodities providing a communications and synchronization infrastructure for the transmission of low-voltage measurements. Third, these ubiquitous measurement points exist in an interconnected fashion irrespective of utility boundaries. This work offers insight into which parameters are meaningful to monitor at the distribution level and provides applications that add unprecedented value to the data extracted from this level. System models comprising the entire Eastern Interconnection are exploited in conjunction with a bounty of distribution level measurement data for the development of wide-area disturbance detection, classification, analysis, and location routines. The main contributions of this work are fivefold: the introduction of a novel power system disturbance detection algorithm; the development of a power system oscillation damping analysis methodology; the development of several parametric and non-parametric power system disturbance location methods, new methods of power system phenomena visualization, and the proposal and mapping of an online power system event reporting scheme. / Ph. D.

A variety of factors such as increasing electrical energy demand, slow expansion of transmission infrastructures, and electric energy market deregulation, are forcing utilities and system operators to operate power systems closer to their design limits. Operating under stressed regimes can have a detrimental effect on the rotor-angle stability of the system. This stability reduction is often reflected by the emergence or worsening of poorly damped low-frequency electromechanical oscillations. Without appropriate measures these can lead to costly blackouts. To guarantee system security, operators are sometimes forced to limit power transfers that are economically beneficial but that can result in poorly damped oscillations. Controllers that damp these oscillations can improve system reliability by preventing blackouts and provide long term economic gains by enabling more extensive utilization of the transmission infrastructure. Previous research in the use of artificial neural network-based intelligent controllers for power system damping control has shown promise when tested in small power system models. However, these controllers do not scale-up well enough to be deployed in realistically-sized power systems. The work in this dissertation focuses on improving the scalability of intelligent power system stabilizing controls so that they can significantly improve the rotor-angle stability of large-scale power systems. A framework for designing effective and robust intelligent controllers capable of scaling-up to large scale power systems is proposed. Extensive simulation results on a large-scale power system simulation model demonstrate the rotor-angle stability improvements attained by controllers designed using this framework.

In the early 1980s, relaying engineers conceived a technology allowing a huge step forward in the monitoring of power system behavior: the synchrophasor, i.e. the estimation of a phasor representation - amplitude and phase - of a sinusoidal waveform at a given point in time thanks to highly accurate time synchronization of a digital relay. By measuring synchrophasors across the power system several times per second, and centralizing the appropriate information in a hierarchical way through a telecommunication network link, it is now possible to continuously monitor the state of very large systems at a high refresh rate. <p><p>At the beginning, the phase angle information of synchrophasors was used to support or improve the performance of classic monitoring applications, such as state estimation and post-mortem analysis. Later, synchrophasors were found to be valuable for the detection and analysis of phenomena that were not monitored previously, such as system islanding and angular stability. This allows a better understanding of system behavior and the design of remedial actions in cases where system security appears to be endangered. Early detection and even prediction of instabilities, as well as validation and improvement of the dynamic models used for studies, have thus become possible.<p><p>However, a power system is rarely stationary and the assumptions behind the definition of “phasor” are not completely fulfilled because the waveforms' frequency and amplitude are not constant over a signal cycle at fundamental frequency. Therefore, accuracy of synchrophasor measurements during dynamic events is an important performance criterion. Furthermore, when discontinuities (phase jumps and high magnitude variations) and harmonics disturb the measured analog signals as a consequence of switching actions or external disturbances, measurements provided to the “user” (the operator or the algorithms that will take decisions such as triggering alarms and remedial actions) require a certain robustness. <p><p>The efforts underpinning this thesis have lead to the development of a method that ensures the robustness of the measurement. This scheme is described and tested in various conditions. In order to achieve a closer alignment between required and actual measurement performance, it is recommended to add an online indicator of phasor accuracy to the phasor data. <p><p>Fast automated corrective actions and closed-loop control schemes relying on synchrophasors are increasingly deployed in power systems. The delay introduced in the measurement and the telecommunication can have a negative impact on the efficiency of these schemes. Therefore, measurement latency is also a major performance indicator of the synchrophasor measurement. <p><p>This thesis illustrates the full measurement chain, from the measurement of analog voltages and currents in the power system to the use of these measurements for various purposes, with an emphasis on real-time applications: visualization, triggering of alarms in the control room or remedial actions, and integration in closed-loop controls. It highlights the various elements along this chain, which influence the availability, accuracy and delay of the data. <p><p>The main focus is on the algorithm to estimate synchrophasors and on the tradeoff between accuracy and latency that arises in applications for which measurements are taken during dynamic events and the data must be processed within a very limited timeframe. <p><p>If both fast phasors and slower, more accurate phasors are made available, the user would be able to select the set of phasors that are the most suitable for each application, by giving priority to either accuracy or a short delay.<p><p>This thesis also tentatively identifies gaps between requirements and typical measurements in order to identify current barriers and challenges to the use of wide area measurement systems. <p><p>A specific application, the continuous monitoring of oscillatory stability, was selected in order to illustrate the benefits of synchrophasors for the monitoring, analysis and control of power system behavior. This application requires a good phasor accuracy but can allow for some measurement delay, unless phasor data are used in an oscillation damping controller. In addition, it also relies on modal estimators, i.e. techniques for the online identification of the characteristics of oscillatory modes from measurements. This field of ongoing research is also introduced in this thesis. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The objective of this dissertation is to investigate the factors that influence the design of wide-area wavelength division multiplexing (WDM) optical networks. Wide-area networks are presented as communication networks capable of transporting voice and data communication over large geographical areas. These networks typically span a whole country, region or even continent.The rapid development and maturation of WDM technology over the last decade have been well-received commercially and warrants the development of skills in the field of optical network design.The fundamental purpose of all communication networks and technologies is to satisfy the demand of end-users through the provisioning of capacity over shared and limited physical infrastructure. Consideration of the business aspects related to communications traffic and the grooming thereof are crucial to developing an understanding of customer requirements in terms of the selection and quality of services and applications. Extensive communication networks require complex management techniques that aim to ensure high levels of reliability and revenue generation.An integrated methodology is presented for the design of wide-area WDM optical networks. The methodology harnesses physical, logical, and virtual topologies together with routing and channel assignment (RCA) and clustering processes to enhance objectivity of the design process. A novel approach, based on statistical clustering using the Ward linkage as similarity metric, is introduced for solving the problem of determining the number and positions of the backbone nodes of a wide-area network, otherwise defined as the top level hub nodes of the multi-level network model. The influence of the geographic distribution of network traffic, and the intra/inter-cluster traffic ratios are taken into consideration through utilisation of modified gravity models and novel network node weighting. / Dissertation (MEng)--University of Pretoria, 2005. / Electrical, Electronic and Computer Engineering / unrestricted

The purpose of this project is to build a working intranet containing core applications that create the framework for a small business intranet. Small businesses may benefit from an intranet because of its ability to effectively streamline the processes for retrieving and distributing information. Intranets are internal networks using TCP/IP protocols, Web server software, and browser client software to share information created in HTML within an organization, and to access company databases.

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