The detection, prevention and mitigation of cascading outages in the power system

This dissertation studies the causes and mechanism of power system cascading outages and develops new methods and new tools to help detect, prevent and mitigate the outages. Three effective solutions: a steady state control scheme, a transient stability control scheme, and an interactive system-wide and local scheme have been proposed using those new methods and tools. A steady state control scheme can help detect and prevent the possible cascading outage at its initial slow steady state progress stage. It uses new methods and new tools to solve the line overload, congestion or bus high/low voltage problems. New methods, such as vulnerability index (VI), margin index (MI), network contribution factor (NCF), topology processing and selected minimum load shedding (SMLS), and new tools, such as transmission network control based on a network contribution factor (NCF) method, generator control based on a generator distribution factor (GDF) method, and load control based on a load distribution factor (LDF) method have been proposed and developed. A transient stability control scheme can help prevent and mitigate the possible cascading outage at its transient progress stage if there is enough time to take action. It uses one Lyapunov direct method, potential energy boundary surface (PEBS) method, and sensitivity analysis of transient energy margin for fast stabilizing control. The results are verified by the accurate time-domain transient stability analysis method. The interactive scheme takes advantage of accurate system-wide and local information and analysis results, uses some techniques from both steady state control and transient stability control, works at both the system-wide level and local substation level, monitors the system all the time, and takes actions when needed to help detect, prevent and mitigate the possible cascading outage. Comprehensive simulation studies have been implemented using the IEEE 14- bus, 24-bus, 39-bus and 118-bus systems and promising results show the ability of the proposed solutions to help detect, prevent and mitigate cascading outages

Coordination of impedance controllers and flexible power for curative congestion management in real-time applications

As the share of feed-in from renewable energy sources rises in German electricity grids, established preventive congestion management processes are called into question. Curative congestion management may increase the utilization of already existing grid capacity without the large investments necessary for conventional grid expansion. The curative paradigm shift requires fast reacting remedial measures, such as innovative power flow controlling devices, as well as reliable algorithms to determine and activate them in due time. This work shows how an automated system can coordinate distributed FACTS devices, that influence a power line's series reactance, and active power from flexible units to solve line overloads in high voltage grids. First, linear sensitivities for gradual reactance changes are derived. Based on this, an optimization and a heuristic approach for automated curative coordination of both types of remedial measures is conceptualized as well as implemented and tested in simulations. Then, the heuristic approach is implemented within a distributed agent-based control algorithm, along with fallback strategies to be executed if agent communication fails. This system is then tested in a laboratory setup to evaluate its real-time applicability. The laboratory setup consists of multiple (Power) Hardware-in-the-Loop modules to create an experimental environment considering many real-world factors that are usually neglected in software simulations. This way, not just the agent algorithm itself, but also the influence of communication delays, reaction times of real power flow controlling devices as well as the integration into a control center environment are evaluated

Water Quality in Drinking Water Distribution Systems

Safe drinking water is paramount for the health and wellbeing of all human populations. Water is extracted from surface and groundwater sources and treated to comply with drinking water standards. The water is then circulated through the drinking water distribution system (DWDS). Within the DWDS, water quality can deteriorate due to microbiological growth, chemical reactions, interactions with ageing and deteriorating infrastructure, and through maintenance and repair activities. Some DWDS actions may serve to improve water quality; however, these can adversely impact the drinking water system and cause instances of poor water quality or disease outbreaks. We invited papers covering examinations of DWDS design and operational practices and their impact on water quality. We received papers based on practical research in real DWDS and laboratory test facilities. We also received papers on novel modelling approaches. A wide range of water quality aspects was gathered, including temperature, disinfection, bacterial communities and biofilm, (fecal) contamination and QMRA, and the effects of flushing and intermittent supply

The detection, prevention and mitigation of cascading outages in the power system

This dissertation studies the causes and mechanism of power system cascading outages and develops new methods and new tools to help detect, prevent and mitigate the outages. Three effective solutions: a steady state control scheme, a transient stability control scheme, and an interactive system-wide and local scheme have been proposed using those new methods and tools. A steady state control scheme can help detect and prevent the possible cascading outage at its initial slow steady state progress stage. It uses new methods and new tools to solve the line overload, congestion or bus high/low voltage problems. New methods, such as vulnerability index (VI), margin index (MI), network contribution factor (NCF), topology processing and selected minimum load shedding (SMLS), and new tools, such as transmission network control based on a network contribution factor (NCF) method, generator control based on a generator distribution factor (GDF) method, and load control based on a load distribution factor (LDF) method have been proposed and developed. A transient stability control scheme can help prevent and mitigate the possible cascading outage at its transient progress stage if there is enough time to take action. It uses one Lyapunov direct method, potential energy boundary surface (PEBS) method, and sensitivity analysis of transient energy margin for fast stabilizing control. The results are verified by the accurate time-domain transient stability analysis method. The interactive scheme takes advantage of accurate system-wide and local information and analysis results, uses some techniques from both steady state control and transient stability control, works at both the system-wide level and local substation level, monitors the system all the time, and takes actions when needed to help detect, prevent and mitigate the possible cascading outage. Comprehensive simulation studies have been implemented using the IEEE 14- bus, 24-bus, 39-bus and 118-bus systems and promising results show the ability of the proposed solutions to help detect, prevent and mitigate cascading outages

Dynamic operation, efficient calibration, and advanced data analysis of gas sensors : from modelling to real-world operation

This thesis demonstrates the use of dynamic operation, efficient calibration and advanced data analysis using metal oxide semiconductor (MOS) gas sensors as an example – from modeling to real-world operation. The necessary steps for an applicationspecific, selective indoor volatile organic compound (VOC) measurement system are addressed, analyzed and improved. Factors such as sensors, operation, electronics and calibration are considered. The developed methods and tools are universally transferable to other gas sensors and applications. The basis for selective measurement is temperature cyclic operation (TCO). The model-based understanding of a semiconductor gas sensor in TCO for the optimized development of operating modes and data evaluation is addressed and, for example, the tailored and stable detection of short gas pulses is developed. Two successful interlaboratory tests for the measurement of VOCs in independent laboratories are described. Selective measurements of VOCs in the laboratory and in the field are successfully demonstrated. Calibrations using the proposed techniques of randomized design of experiment (DoE), model-based data evaluation and calibration with machine learning methods are employed. The calibrated models are compared with analytical measurements using release tests. The high agreement of the results is unique in current research.Diese Thesis zeigt den Einsatz von dynamischem Betrieb, effizienter Kalibrierung, und fortschrittlicher Datenanalyse am Beispiel von Metalloxid Halbleiter (MOS) Gassensoren – von der Modellierung bis zum realen Betrieb. Die notwendigen Schritte für ein anwendungsspezifisches, selektives Messystem für flüchtige organische Verbindungen (VOC) im Innenraum werden adressiert, analysiert und verbessert. Faktoren wie z.B. Sensoren, Funktionsweise, Elektronik und Kalibrierung werden berücksichtigt. Die entwickelten Methoden und Tools sind universell auf andere Gassensoren und Anwendungen übertragbar. Grundlage für die selektive Messung ist der temperaturzyklische Betrieb (TCO). Auf das modellbasierte Verständnis eines Halbleitergassensors im TCO für die optimierte Entwicklung von Betriebsmodi und Datenauswertung wird eingegangen und z.B. die maßgeschneiderte und stabile Detektion von kurzen Gaspulsen entwickelt. Zwei erfolgreiche Ringversuche zur Messung von VOCs in unabhängigen Laboren werden beschrieben. Selektive Messungen verschiedener VOCs im Labor und im Feld werden erfolgreich demonstriert. Dabei kommen Kalibrierungen mit den vorgeschlagenen Techniken des randomisierten Design of Experiment (DoE), der modellbasierten Datenauswertung und Kalibrierung mit Methoden des maschinellen Lernens zum Einsatz. Die kalibrierten Modelle werden anhand von Freisetzungstests mit analytischen Messungen verglichen. Die hohe Übereinstimmung der Ergebnisse ist einzigartig in der aktuellen Forschung

New tools for improving culture strategies for Hepatocyte differentiation

Tese de mestrado. Biologia (Biologia Molecular e Genética). Universidade de Lisboa, Faculdade de Ciências, 2011O fígado é um órgão de enorme importância fisiológica e metabólica. Os hepatócitos, que constituem cerca de 80% da massa total de fígado, são frequentemente expostos a agentes tóxicos podendo levar à sua perda, limitando a função hepática 1. Apesar da capacidade regenerativa destas células, o recurso ao transplante de fígado é frequente, no entanto, o número de dadores disponíveis é um factor limitante desta terapia. Os hepatócitos primários humanos e dispositivos hepáticos bioartificiais (BAL) podem ser utilizados como alternativa terapêutica. Porém, a reduzida capacidade proliferativa ex vivo dos hepatócitos, a perda do perfil de expressão hepática e da sua funcionalidade limitam o seu potencial terapêutico, aquando mantidos em cultura ao longo do tempo 2. Estas células possuem ainda um enorme potencial no desenvolvimento de novos modelos in vitro para ensaios pré-clínicos, na descoberta de novos fármacos e em testes toxicológicos. Em terapias hepáticas têm sido utilizadas fontes alternativas de células do fígado, nomeadamente, progenitores hepáticos (com capacidade de maturar em hepatócitos e colangiócitos, as principais células presentes no fígado), células estaminais da medula óssea e células estaminais embrionárias (CEEs). Apesar de todas estas fontes alternativas apresentarem limitações na produção de hepatócitos, as células estaminais embrionárias humanas (CEEhs) são consideradas uma potencial fonte ilimitada de células com uma enorme aplicabilidade neste tipo de terapias. Vários estudos têm mostrado a capacidade destas originarem células com características hepáticas3,4. Os processos de diferenciação hepática a partir de CEEhs reflectem o desenvolvimento do fígado in vivo, onde, numa primeira fase, as CEEhs originam células de endoderme definitiva (ED). Estas por sua vez diferenciam-se em progenitores hepáticos que maturam dando origem aos hepatócitos adultos. Têm sido desenvolvidos protocolos que visam melhorar as condições de cultura com posterior optimização da diferenciação, tais como o recurso a factores de crescimento essenciais para a diferenciação ou ao uso de uma matriz extracelular (MEC), que constitui uma rede de macromoléculas que influencia a migração, a polarização e, consequentemente, a funcionalidade das células. Contudo, estes protocolos apresentam duas grandes desvantagens: (1) o número de hepatócitos produzidos a partir de CEEhs durante o processo de diferenciação é insuficiente para posterior aplicação em BAL (para o qual são necessários 10 mil milhões de hepatócitos) e (2) o tipo de células obtido no final da diferenciação não revela um fenótipo caracteristico de hepatócitos maduros, apresentando uma população altamente heterogénea de células indiferenciadas, progenitoras e com carácter maduro. Portanto, o processo de diferenciação hepática necessita de ser optimizado, de modo a aumentar significativamente o rendimento de hepatócitos funcionais e a pureza da população obtida no final do mesmo. Numa perspectiva de optimização, a monitorização de todo o processo de diferenciação é essencial para caracterizar e identificar as células específicas de cada etapa do mesmo, permitindo deste modo avaliar de forma precisa a sua eficiência. Actualmente, as técnicas existentes para esta caracterização são invasivas, morosas e inadequadas quando se pretende definir da melhor forma a optimização do bioprocesso. Como alternativa têm sido desenvolvidas estratégias para modificar geneticamente as CEEhs, como por exemplo, o uso de genes repórter fluorescentes, para marcar especificamente um determinado tipo celular proveniente de CEEhs. A introdução destes genes fluorescentes, sob o controlo de promotores específicos de cada tipo celular torna possível essa marcação específica, tirando partido de técnicas não-invasivas. Um dos genes repórter mais utilizado é a variante da proteína verde fluorescente (eGFP; do inglês, enhanced Green Fluorescent Protein). Ultimamente, têm sido publicados alguns estudos que utilizam esta técnica para identificar e isolar uma linhagem derivada de CEEhs. Apesar da utilidade desta técnica na optimização do processo de diferenciação, continua a ser necessário o desenvolvimento de uma estratégia que monitorize em tempo-real todas as etapas deste processo. Tendo em conta as etapas cruciais durante o desenvolvimento do fígado, é possível visualizar e acompanhar todo o processo recorrendo à expressão de dois genes repórter, controlados por diferentes sequências reguladoras específicas de cada etapa do desenvolvimento. Os métodos mais utilizados para transferência génica são os vectores virais, em particular os vectores lentivirais (VLs) baseados no Vírus da Imunodeficiência Humana (VIH), devido à sua eficiência na transferência génica e expressão estável ao longo do tempo. Estes vectores demonstram também maior resistência ao silenciamento em CEEs, comparativamente aos restantes vectores virais, sendo uma poderosa ferramenta na transferência génica nestas células. Assim, foram desenvolvidos vectores lentivirais inactivados (SIN; do inglês, Self-Inactivating), caracterizados por possuirem uma delecção na região U3 da longa repetição terminal a 3‟ (LTR; do inglês, Long Terminal Repeat) de modo a que a expressão do genoma viral na célula hospedeira seja controlada apenas pelos promotores exogenos, que controlam a expressão dos genes repórter, levando à perca da capacidade replicativa dos vectores lentivirais e tornando-os deste modo seguros. Neste contexto, desenvolveu-se uma nova ferramenta baseada na construção de vectores lentivirais inactivados duplo-repórter (VLs-SIN), que contém dois genes repórter, Cherry e eGFP, controlados por promotores independentes que permitem a monitorização em tempo-real das principais etapas. Inicialmente, para comprovar a presença de duas unidades transcripcionais independentes no sistema desenvolvido, foram clonados dois promotores constitutivos para regularem a expressão dos dois repórteres. A expressão de cada repórter é controlada apenas pelo promotor a montante do mesmo, evidenciando uma expressão independente. Por outro lado, uma célula que ostenta o vector duplo, com os dois genes repórter a serem transcritos por dois promotores independentes mas activos no mesmo espaço temporal (neste caso, promotores de genes constitutivos), co-expressa os dois genes fluorescentes. Após a validação inicial deste sistema e com a produção dos VLs-SIN, a clonagem suplementar de sequências de poliadenilação (uma sequência de poliadenilação sintética seguida de uma sequência espaçadora não codificante) entre as duas unidades transcripcionais levou à optimização do nível da expressão dos dois repórteres, diminuindo a variação da expressão de ambos, quando expressos constitutivamente na população genéticamente modificada. Por outro lado, a desvantagem apresentada pela proteína vermelha fluorescente DsRED em relação às proteínas vermelhas fluorescentes monoméricas, como por exemplo a mCherry, levou-nos à substituição do gene repórter DsRED pelo gene que codifica a proteína mCherry. Esta proteína apresenta uma maior foto-estabilidade, sendo um factor crítico na monitorização ao longo do tempo. No entanto, apesar da diminuição da expressão deste repórter em relação ao nível de expressão apresentado pela DsRED, a conjugação dos repórteres mCherry e eGFP no sistema duplo-repórter mostrou ser a mais promissora. Assim, foram desenvolvidos três VLs-SIN duplo-repórter (mCherry e eGFP) para transferência génica de marcadores específicos das etapas cruciais do processo de diferenciação hepática. Os promotores clonados mostraram especificidade e eficácia na expressão dos repórteres durante o processo de validação numa linha celular de hepatocarcinoma humano HepG2. Esta linha celular é normalmente utilizada como modelo in vitro em estudo de metabolismo de hepatócitos humanos devido à sua capacidade de expressar genes hepáticos fetais. Os resultados obtidos demonstram a capacidade desta nova ferramenta em caracterizar e identificar as células específicas de cada etapa da diferenciação de CEEhs em hepatócitos. Este sistema poderá permitir a monitorização da diferenciação numa linhagem específica, e de uma forma mais eficaz a optimização de todas as condições de cultura para expansão e diferenciação. Por outro lado, esta nova ferramenta desenvolvida mostrou-se promissora quanto à posterior aplicação em estudos do perfil de expressão génica para monitorizar a resposta a determinados estímulos. Assim, este estudo contribuirá futuramente para o progresso no campo da biologia das células estaminais e sua aplicabilidade.Owing the scarcity of human hepatocytes for application in the pre-clinical drug development and bioartificial liver (BAL) devices, human embryonic stem cells (hESCs) presents a great potential for the production of hepatocytes through the hepatic differentiation process. However, this often results in not fully functional final cell type obtained and low-yield, which presently are the main limitations of the differentiation process. Furthermore, the traditional methods for identification of stage-specific cell type are based on time-consuming and invasive methodologies that are not a practical approach when the goal is bioprocess optimization aiming for the generation of well-defined cell populations. The analysis of hESCs differentiation stages would therefore greatly profit from in vivo and real-time monitoring methodologies. In this work, we designed a series of dual-reporter Self-Inactivating Lentiviral Vectors (SIN-LVs) carrying two independent transcriptional units to be expressed in vivo during different stages of hepatocyte differentiation. These SIN-LVs were validated in human hepatocellular liver carcinoma cell line HepG2 suitable as an in vitro model system for the study of human hepatocytes and the promoters‟ specificity were confirmed. This design enables a reliable and efficient visualization and trafficking of stem cells and their derivatives using live imaging non-invasive techniques, contributing for debottlenecking the optimization of hepatocyte differentiation and expansion conditions. Additionally, cells expressing these markers can also be extremely valuable tools for basic studies of stem cell biology and pre-clinical drug development

Advances in Ecohydrology for Water Resources Optimization in Arid and Semi-arid Areas

This Special Issue (SI) aims to investigate the relationships between hydrological and ecological processes and how these interactions can contribute to the optimization of water resources in arid and semi-arid areas. This SI collected 10 original contributions on sustainable land management and the optimization of water resources in fragile environments that are at elevated risk due to climate change. The topics mainly concern transpiration, evapotranspiration, groundwater recharge, deep percolation, and related issues. The collection of manuscripts presented in this SI represents a contribution of knowledge in ecohydrology

An Integrated Security-constrained Model-based Dynamic Power Management Approach for Isolated Microgrid Power Systems

Microgrid power systems draw lots of interests in marine, aerospace, and electric vehicle applications and are drawing increased attention for terrestrial applications. These power systems, however, are prone to large frequency and voltage deviations, when disturbances happen. Therefore, an effective power management method is needed to operate microgrids optimally, while satisfying operating and security constraints. In this dissertation, a new Integrated Security-Constrained Power Management (ISCPM) method is presented for isolated microgrid power systems during normal/alert operating states. The new ISCPM method was formulated as a multi-objective optimal control problem, in which set-points of several system control methods are minimally adjusted, subject to operating and security constraints, over a period in the future. To solve the ISCPM multi-objective optimal control problem, an evolutionary algorithm based on the Nondominated Sorting GA II (NSGA-II) was developed, in which the optimization solver is linked to a fast simulation core. A fuzzy membership based method was developed to identify the best compromise solution. The new power management method was implemented on a notional computer model for an all-electric ship. The NSGA-II was developed in MATLAB, by adapting a general purpose GA toolbox, IlliGAL. To conduct transient simulations during the GA iterations, the simulation core of the TSAT Tool of Tools TM software package was used. The best compromise solution identification method was developed in MATLAB. To illustrate how the new ISCPM method works in the notional all-electric ship model, several case studies were presented. Also, to evaluate the performance of the new ISCPM method, extensive studies were conducted. For these studies, a detailed electromagnetic transient model of the system in PSCAD was used. The performance analysis addressed quality of the new method from power system operation and multi-objective optimization perspectives. The results indicated that the new ISCPM method could effectively operate the system in an overall near-optimal condition, in which security and operating constraints are also satisfied. The application of the new power management method is not limited to all-electric shipboard power systems and it has great potential to be extended to other types of isolated microgrid power systems

The 1995 Goddard Conference on Space Applications of Artificial Intelligence and Emerging Information Technologies

This publication comprises the papers presented at the 1995 Goddard Conference on Space Applications of Artificial Intelligence and Emerging Information Technologies held at the NASA/Goddard Space Flight Center, Greenbelt, Maryland, on May 9-11, 1995. The purpose of this annual conference is to provide a forum in which current research and development directed at space applications of artificial intelligence can be presented and discussed