A real-time algorithm is developed for the detection of series dc arc faults in a grid-tie solar photovoltaic (PV) installation. The sensed dc bus current, which is sampled using an analog-to-digital converter with Galvanic isolation, is filtered using a wavelet-based, two-level filter bank. The filter bank, referred to as the post-processing filter, improves the robustness of the algorithm to any false tripping by rejecting power converter harmonics that are added to the dc bus current. To determine if a fault has occurred, the algorithm calculates the variance of the filter bank output and sees if the calculated variance exceeds an upper threshold value. If the upper threshold is exceeded, and the dc bus voltage falls below a predefined lower limit for a set number of instances, the algorithm trips. The algorithm can detect a series arc fault in under two seconds and does not rely on machine learning techniques to process the sensed signal. The detection algorithm is implemented on a commercial microcontroller using C code, and the filter bank convolutions are implemented using 32-bit floating point variables. / Master of Science / A device is developed for the detection of series dc arc faults in solar photovoltaic installations. Dc arc faults that result from loose connections or worn cable insulation can go unnoticed by most conventional fault detectors. Once it has ignited, the series arc can generate considerable amounts of heat and poses a significant fire risk. By contributing to the development of a dc arc fault detection system, the intention is that dc renewable energy distribution systems, most notably solar photovoltaic installations, can gain even more widespread adoption. This would make a significant impact towards decarbonizing the energy sector and tackling the threat to society posed by climate change.

The injection of varying fuel-air mixtures into a vitiated, high-speed crossflow is investigated at five atmosphere chamber pressure in this work. The experimental facility has two combustion stages: a headend stage to create the vitiated crossflow and an axial stage injected into an optically accessible test section. The crossflow entered the test section at a velocity of 76 m/s and a temperature of 1750 K. The axial jet mixtures were first investigated at lean equivalence ratio conditions with hydrogen fuel mole fractions up to 100% to study hydrogen enrichment at lower reactivity. Separately, axial hydrogen fuel content was increased at a constant flame temperature of about 1770K to better understand the jet behavior at temperature conditions relevant to power generation industry combustors. The jet velocity for these cases is maintained at 120 m/s to investigate an increased momentum flux ratio. High-speed chemiluminescence was utilized to examine the flame behavior of the reacting jets. Additionally, emissions measurements were taken to quantify the increase in NOx emissions that is expected to occur with larger hydrogen fuel contents. Particle image velocimetry (PIV) imaging was taken for select points to obtain information on the flow field dynamics. For the methane air jets, increasing premixing led to reduced flame stability within the test section viewing window at the equivalence ratios tested Increasing jet hydrogen fraction leads to greater stabilization of the leeward jet flame near the axial injector location the tested equivalence ratios, and the stabilization of a windward flame not present in the methane jets at these velocities. Higher levels of NOx emissions were found to occur with increased equivalence ratio and reduced premixing, which are tied to reduced flame liftoff height, and when a scaling factor is applied higher jet hydrogen levels also led to increased emissions.

Yes / The advent of smart meter technology has enabled periodic monitoring of consumer energy consumption. Hence, short term energy forecasting is gaining more importance than conventional load forecasting. An Accurate forecasting of energy consumption is indispensable for the proper functioning of a virtual power plant (VPP). This paper focuses on short term energy forecasting in a VPP. The factors that influence energy forecasting in a VPP are identified and an artificial neural network based energy forecasting model is built. The model is tested on Sydney/ New South Wales (NSW) electricity grid. It considers the historical weather data and holidays in Sydney/ NSW and forecasts the energy consumption pattern with sufficient accuracy.

[ES] Esta tesis evalúa ciclos de producción de oxígeno que usan membranas en tres contextos industriales, enfatizando en la producción de potencia operando bajo oxicombustión. La principal motivación es reducir las emisiones contaminantes sin afectar el desempeño del sistema. Se ha realizado un análisis termoeconómico de un ciclo de producción de oxígeno basado en membranas para evaluar la viabilidad de estas instalaciones en una planta de cerámica. El ciclo se impulsa por gases reciclados de la planta y usa turbogrupos e intercambiadores de calor para comprimir y calentar el aire para extraer su oxígeno. Dos configuraciones han sido estudiadas, encontrándose un costo óptimo de producción de 31e/t, competitivo cuando se considera un precio medio de mercado de 50e/t. Comparado con otros métodos de producción de oxígeno, este ciclo es competitivo en lo que respecta a la pureza y producción del oxígeno y el consumo energético. Esto motivó el estudio de configuraciones similares operando en dos contextos de generación de potencia que usan con oxicombustión: una planta de generación eléctrica y un motor de encendido provocado. En el primer contexto, se compara el desempeño de dos métodos de producción de oxígeno, operando en una planta de generación eléctrica (Ciclo Graz), que usa separación criogénica de aire como fuente de oxígeno, siendo el caso base del análisis. Se consideran dos configuraciones de membrana: de tres y cuatro entradas, cuya fuente de energía es un flujo de temperatura media dentro del ciclo de potencia. La configuración con una membrana de tres entradas mejora la eficiencia del caso base en un 0.61 %, y la de cuatro entradas en un 2.3 %. La producción de oxígeno requiere un menor consumo energético que en el caso base en las configuraciones de membrana, aumentando la salida de potencia neta del caso base. Por tanto, la producción de oxígeno con membranas muestra un desempeño prometedor, con una posible integración con una planta de producción de potencia que trabaja con oxicombustión. En el segundo contexto, el ciclo de membrana se acopla a un motor de encendido provocado. Distintas condiciones de operación son evaluadas en términos del consumo de combustible y disponibilidad de energía para la producción de oxígeno. La fuente de energía del ciclo de membrana es el flujo de gases de escape del motor. Primeramente, distintas concentraciones de oxígeno y relaciones de compresión del motor son estudiadas a un régimen medio, comparando el desempeño con la operación convencional del motor. Una concentración media (30 %) fue hallada como óptima en el estudio, cuyas condiciones de operación permiten un aumento considerable de la relación de compresión del motor. En segundo lugar, se realiza un estudio de plena carga del motor en un rango amplio de regímenes de giro del motor. El motor de oxicombustión alcanza una operación sostenible en los regímenes estudiados, alcanzando los valores de referencia de plena carga. Se han obtenido consumos de combustible similares al caso convencional más eficiente cuando la relación de compresión es elevada en el caso de oxicombustión. En tercer lugar, se han encontrado límites operativos en cargas parciales y altitud. La tendencia de consumo de combustible del caso con oxicombustión es similar a un motor convencional sobrealimentado a cargas parciales, mejorando el desempeño de un motor de aspiración natural. La menor carga alcanzable esta entre 40-50% de la máxima carga, dependiendo de la relación de compresión del motor. Por otro lado, el sistema muestra un desempeño adecuado hasta los 4000 m de altitud. Se concluye que el ciclo de producción de oxígeno basado en membranas de separación de aire muestra flexibilidad para operar en un amplio rango de energía disponible, mostrando un desempeño adecuado de acuerdo con los requerimientos del sistema. Adicionalmente, se encuentran posibles ventajas en cuanto al consumo de energía y costos operativos realizando un diseño cuidadoso. / [CA] Aquesta tesi avalua cicles de producció d'oxigen que usen membranes en tres contextos industrials, emfatitzant en la producció de potencia operant amb oxicombustió. La principal motivació es reduir les emissions contaminants sense afectar el funcionament del sistema.S'ha realitzat una anàlisi termoeconómico d'un cicle de producció d'oxigen basat en membranes per a avaluar la viabilitat d'aquestes instal·lacions en una planta de ceràmica. El cicle s'impulsa per gasos reciclats de la planta i usa turbogrupos i intercanviadors de calor per a comprimir i calfar l'aire per a extraure el seu oxigen. Dues configuracions han sigut estudiades i s'ha trobat un cost òptim de producció d'oxigen de 31e/t, que es competitiu quan es considera un preu de mercat de 50e/t. Comparat amb altres mètodes de producció d'oxigen, aquest cicle mostra un comportament competitiu pel que fa a puresa d'oxigen, producció i consum energètic. Això va motivar l'estudi de configuracions similars operant en dos contexts diferents de generació de potencia que operen amb oxicombustió: una planta de generació elèctrica i un motor d'encesa provocada.En el primer context, s'ha comparat el funcionament de dos mètodes de producció d'oxigen diferents, operant amb una planta de generació elèctrica (cicle Graz), que usa separació criogènica d'aire com a font d'oxigen, sent el cas base de l'anàlisi. S'han considerat dues configuracions de membrana: de tres i quatre entrades, la font d'energia de les quals és un flux de temperatura mitjana dins del cicle de potència. La configuració amb una membrana de tres entrades millora l'eficiència del cas base amb un 0.61 %, mentre que la de quatre entrades comporta una millora d'un 2.3 %. La producció d'oxigen requerix menys consum energètic que en el cas base en les dues configuracions de membrana, augmentant l'eixida de potencia neta del cas base. Per tant, la producció d'oxigen amb membranes mostra un funcionament prometedor, amb una possible integració amb una planta de producció de potencia que treballa amb oxicombustió.En el segon context, el cicle de membrana s'acobla a un motor d'encesa provocada. Diferents condicions d'operació han sigut avaluades en termes de consum de combustible i disponibilitat d'energia per a la producció d'oxigen. La font d'energia per a la producció d'oxigen es el flux de gasos d'escapament del motor. Primerament, diferents concentracions d'oxigen i relacions de compressió del motor han sigut estudiades a un regim mitja, comparant el funcionament amb el d'un motor convencional. Una concentració mitjana (30%) va ser trobada com a òptima en l'estudi, les condicions d'operació del qual permeten un augment considerable de la relació de compressió del motor. En segon lloc, s'ha realitzat un estudi a plena carrega del motor en un rang ampli de règims de gir del motor. El motor d'oxicombustió aconseguix una operació sostenible en els règims estudiats, aplegant als valors de referencia a plena carrega. S'han obtingut consums de combustible similars al cas d'operació convencional mes eficient quan la relació de compressió es elevada en el cas d'oxicombustió.En tercer lloc, s'han trobat límits operatius referents a l'operació a carregues parcials i altitud. La tendència de consum de combustible del cas amb oxicombustió es similar a la d'un motor convencional sobrealimentat a carregues parcials, mentre que millora el funcionament d'un motor d'aspiració natural. La menor carrega assolible esta entre 40-50% de la màxima carrega, depenent de la relació de compressió del motor. Per una altra banda, el sistema mostra un funcionament adequat fins als 4000m d'altitud. Es pot dir que el cicle de producció d'oxigen basat en membranes de separació d'aire mostra flexibilitat per a operar en un rang ampli d'energia disponible, mostrant un funcionament adequat d'acord amb els requeriments del sistema. Addicionalment, es poden trobar posibles avantatges en consum d'energia i costs operatius realitzant un disseny cuidadós. / [EN] This thesis assesses oxygen production cycles based on membranes in three industrial situations, emphasizing power production operating under oxycombustion. The primary motivation is the reduction of pollutant emissions while not affecting the system's thermal efficiency.Thus, a thermoeconomic analysis of a membrane-based oxygen production cycle is performed to assess the viability of these facilities in the context of a ceramic plant. The cycle is driven by recycling gases within the plant and uses turbochargers and heat exchangers to compress and heat the air for oxygen obtention. Two configurations were studied, finding an optimum oxygen production cost of 31e/t was found, being competitive when compared with an average wholesale market price of 50e/t. Compared with other oxygen production methods, this cycle exhibits a competitive behavior regarding oxygen purity, production, and energy consumption. The promising results of this analysis motivate the study of similar configurations working in two oxycombustion contexts: a power plant and a spark-ignition engine. Two oxygen production methods operating with a power production plant (Graz cycle) are compared in the first context. The power plant uses cryogenic air separation as its oxygen source, the baseline in this analysis. Therefore, two membrane configurations are considered: three-end and four-end membranes. A medium-temperature stream within the power production cycle is the energy source to drive the membrane cycles. Both cases are compared with the baseline Graz cycle operation. The three-end membrane-based cycle improves the baseline efficiency by 0.61% and the four-end by 2.30 %. The oxygen production requires less power consumption in the membrane cases than in the baseline, increasing the net power output. Thus, membrane-based cases display a promising performance, with possible integration within an oxycombustion power plant. In the second context, the membrane-based cycle is coupled within an oxycombustion spark-ignition engine, where different operation conditions are evaluated regarding fuel consumption and energy availability for oxygen production. The energy source to drive the membrane-based cycle is the exhaust gases stream. As a first step, different oxygen concentrations and engine compression ratios are studied at medium speed, comparing the performance with the engine's conventional operation. Medium oxygen concentration (30 %) was found to be optimum. This concentration allows the operation at a high engine compression ratio. Secondly, a full-load study in a wide range of engine speeds is made. The oxycombustion engine achieves a sustainable operation at the studied speeds, reaching the reference full-load power values. Similar fuel consumptions regarding the most efficient conventional case are achieved when the engine compression ratio is elevated under oxycombustion. Thirdly, operative limits regarding part-load and altitude operation are found. The fuel consumption behavior of the oxycombustion case is similar to a conventional turbocharged engine at part-load while improving a naturally aspirated engine operation. The minimum achievable load is between 40 to 50% of the maximum load, depending on the engine compression ratio. The membrane cycle operation is affected at lower loads. On the other hand, the system shows a suitable performance up to 4000 m. Thus, it can be concluded that the membrane-based oxygen production cycle exhibits flexibility to work in a wide range of available energy, displaying a suitable performance according to the requirements. Additionally, possible advantages in energy consumption and operative costs could be found when a careful design is performed. / The author would like to acknowledge the financial support received through contract ACIF/2020/246 of the Conselleria d’Innovació, Universitats, Ciència i Societat Digital. / Gutiérrez Castro, FA. (2023). Assessment of highly turbocharged oxygen production cycles coupled with power generation systems working under oxycombustion [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/200173

As traditional solar technologies approach theoretical efficiency limits, novel approaches are necessary to continue to improve the power generation capacity of photovoltaics. Two complementary multiexcitonic processes, singlet fission (SF) and triplet-triplet annihilation upconversion (TTA-UC), show great promise in this field, allowing access to regions of the solar spectrum inefficiently harvested by silicon cells. In designing and optimizing systems for SF and TTA-UC, macromolecular scaffolds are particularly attractive, enabling the simultaneous tuning of electronic coupling between chromophores as well as their intermolecular packing. The high modularity of these scaffolds allows for easy adjustment of component ratios or the introduction of new units to further adjust dynamics or morphology. As such, macromolecular systems have also been employed in various condensed and solid phase systems which may more readily be incorporated into photovoltaics. Herein, we expand the scope of macromolecular architectures to new domains for SF and TTA-UC. In Chapter 1, we summarize the guiding principles for the optimization of these processes, and follow with a discussion of existing oligomeric, macromolecular, and self-assembled systems. In Chapter 2, an amphiphilic block copolymer (BCP) is introduced to explore SF in self-assembled micelles. We find that SF dynamics can be controlled by modifying BCP block ratios, as well as by co-assembly with a variety of dopants. In Chapter 3, this amphiphilic BCP scaffold is adapted to TTA-UC, and we highlight the importance of micellar swelling in enabling this process. In Chapter 4, electron donors are incorporated into polymers alongside pendent SF chromophores to explore both intra- and intermolecular charge transfer. We observe the formation of long-lived charge separated states prompted by SF, with dynamics tunable by solvent polarity, donor strength, and mode of interaction. And in Chapter 5, a series of hetero-oligomers are presented to explore SF at interfaces between classic acenes and the less-studied dipyrrolonaphthyridinedione. We reinforce the essential role of charge transfer states in mediating or deactivating singlet fission in a tunable fashion based on chromophore energetics. In sum, this work further demonstrates the essential role macromolecular engineering will play in the continued development of SF and TTA-UC.

Made available in DSpace on 2014-07-29T15:08:18Z (GMT). No. of bitstreams: 1 Previsao de Vazoes Naturais Diarias.pdf: 3835466 bytes, checksum: f927e5c8c3a89c73430512243b55c36c (MD5) Previous issue date: 2012-09-05 / The forecast of natural flows to hydroelectric plant reservoirs is an essential input to the planning and programming of the SIN´s operation. Various computer models are used to determine these forecasts, including physical models, statistical models and the ones developed with the RNA´s techniques. Currently, the ONS performs daily forecasts of natural flows to the UHE Tucuruí based on the univariate stochastic model named PREVIVAZH, developed by Electric Energy Research Center - Eletrobras CEPEL. Throughout the last decade, several papers have shown evolution in the application of neural networks methodology in many areas, specially in the prediction of flows on a daily, weekly and monthly basis. The goal of this dissertation is to present and calibrate a model of natural flow forecast using the RNA´s methodology, more specifically the NSRBN (Non-Linear Sigmoidal Regression Blocks Networks) (VALENCA; LUDERMIR, 2001), on a time lapse from 1 to 12 days forward to the Tucuruí Hydroelectric Plant, considering the hydrometric stations data located upstream from it s reservoir. In addition, a comparative analysis of results found throughout the calibrated neural network and the ones released by ONS is performed. The results show the advantage of the methodology of artificial neural networks on autoregressive models. The Mean Absolute Percentage Error - MAPE values obtained were, on average, 48 % lower than those released by the ONS. / A previsão de vazões naturais aos reservatórios das usinas hidrelétricas é insumo fundamental para o planejamento e operação do SIN. Diversos modelos são utilizados na determinação dessas previsões, entre os quais podem ser citados os modelos físicos, os estatísticos e aqueles baseados na técnica de Redes Neurais Artificiais. Atualmente, o ONS realiza as previsões diárias de vazões naturais para a Usina Hidrelétrica Tucuruí com base no modelo estocástico univariado denominado PREVIVAZH, desenvolvido pelo CEPEL. Ao longo da última década, muitos trabalhos têm mostrado a evolução da aplicação da metodologia de Redes Neurais Artificiais em diversas áreas e em particular na previsão de vazões naturais, para intervalos de tempo diários, semanais e mensais. O objetivo deste trabalho foi calibrar e avaliar um modelo de previsão de vazões naturais, utilizando a metodologia de RNA, mais especificamente as redes construtivas do tipo NSRBN(Non-Linear Sigmoidal Regression Blocks Networks) (VALENCA; LUDERMIR, 2001), no horizonte de 1 até 12 dias à frente, para a Usina Hidrelétrica Tucuruí, considerando as informações advindas de postos hidrométricos localizados à montante do seu reservatório. Adicionalmente, foi realizada uma análise comparativa dos resultados encontrados pela rede neural calibrada e aqueles obtidos e divulgados pelo ONS. Os resultados obtidos mostram a vantagem da metodologia de redes neurais artificiais sobre os modelos auto-regressivos. Os valores do Erro Percentual Médio Absoluto - MAPE foram, em média, 48% inferiores aos divulgados pelo ONS.

Concerns about climate change brought about by the increasing usage of fossil fuels has made it imperative to develop sustainable energy usage based on renewable sources. Micro-hydel plants are an important source of renewable energy that can be exploited to supply requirements of local loads in remote locations while operating as an isolated source, or the larger network when operating in grid connected mode. The focus of this research is to develop an alternative topology to the one currently in use in micro-hydel power plants. While existing plants are based on a ballast-controlled, fixed-speed, operator-supervised model, the proposed work introduces a ballast-free, variable-speed generator capable of unsupervised operation. Conventional micro-hydel generators use o-the-shelf machines with the purported aim of reducing costs. They run at a fixed speed, maintaining constant electrical load by switch-ing a plant-situated ballast load to compensate for consumer load changes. Although the intention is to have a simplified control scheme and reduced costs, the conventional plants end up being expensive since the balance-of-system costs are increased. The plant re-quires supervision by a trained operator and frequent maintenance, failing which the reliability suers. The cost and maintenance reduction possible is analysed by comparing the proposed topology with a typical well designed conventional micro-hydel plant. The proposed topology takes the characteristics of the turbine into account, and by running at variable speed, ensures that only as much power is generated as required by the consumer load. This eliminates the ballast load and associated problems present in conventional plants. The generator can be connected to the grid, if present, enabling the available power to be fully utilized. The behavior of a hydraulic turbine operating at a fixed head and discharge rate with no flow control is analyzed. Based on the turbine characteristics, a generator topology is developed, which operates in a speed range dictated by the characteristics of the turbine. Continual supervision is unnecessary since the operation of the generator is within safe limits at all times. A simple emulator that can mimic the steady state and dynamic behaviour of the turbine is developed to test the proposed generator. The two-machine wound rotor generator proposed has an auxiliary exciter similar to a conventional brushless alternator with the additional provision for bidirectional power transfer. The shaft mounted rotor side electronics facilitate brushless operation, and to-gether with the stator side controllers form an embedded system that does away with having to tune the plant in-situ. The control scheme is evaluated for expected perfor-mance in dierent operating modes. The thesis also discusses an optimization of the synchronous speed of the generator with respect to the turbine characteristics. This minimizes the bidirectional slip power transfer requirements of the rotor side converters and leads to the lowest rating for the auxiliary machine. The proposed generator can then operate like a conventional synchronous gen-erator in the grid connected mode with a simplified control scheme.

Attempts to reduce greenhouse gas emissions are promising with the recent dramatic increase of installed renewable energy sources (RES) capacity. Integration of large intermittent renewable resources affects smart grid systems in several significant ways, such as transient and voltage stability, existing protection scheme, and power leveling and energy balancing. To protect the grid from threats related to these issues, utilities impose rigorous technical requirements, more importantly, focusing on fault ride through requirements and active/reactive power responses following disturbances. This dissertation is aimed at developing and verifying the advanced and algorithmic methods for specification of protection schemes, reactive power capability and power control requirements for interconnection of the RESs to the smart grid systems. The first findings of this dissertation verified that the integration of large RESs become more promising from the energy-saving, and downsizing perspective by introducing a resistive superconducting fault current limiter (SFCL) as a self-healing equipment. The proposed SFCL decreased the activation of the conventional control scheme for the wind power plant (WPP), such as dc braking chopper and fast pitch angle control systems, thereby increased the reliability of the system. A static synchronous compensator (STATCOM) has been proposed to assist with the uninterrupted operation of the doubly-fed induction generators (DFIGs)-based WTs during grid disturbances. The key motivation of this study was to design a new computational intelligence technique based on a multi-objective optimization problem (MOP), for the online coordinated reactive power control between the DFIG and the STATCOM in order to improve the low voltage ride-through (LVRT) capability of the WT during the fault, and to smooth low-frequency oscillations of the active power during the recovery. Furthermore, the application of a three-phase single-stage module-integrated converter (MIC) incorporated into a grid-tied photovoltaic (PV) system was investigated in this dissertation. A new current control scheme based on multivariable PI controller, with a faster dynamic and superior axis decoupling capability compared with the conventional PI control method, was developed and experimentally evaluated for three-phase PV MIC system. Finally, a study was conducted based on the framework of stochastic game theory to enable a power system to dynamically survive concurrent severe multi-failure events, before such failures turn into a full blown cascading failure. This effort provides reliable strategies in the form of insightful guidelines on how to deploy limited budgets for protecting critical components of the smart grid systems.

No description available.

Master of Science / Department of Electrical and Computer Engineering / Anil Pahwa / The unusual weather events during the polar vortex of 2014 illuminated the needs for fuel diversity for power generation in order to allow reliable operation of the electricity grid. A system wide reliability assessment for winter months should be undertaken in addition to the summer months to ensure reliable operation of the electricity grid throughout the year. Severe weather conditions that lead to equipment malfunction during the polar vortex should be thoroughly investigated and remediations to ensure satisfactory future performance of the grid must be undertaken. Environmentally unfriendly emissions from power plants must be minimized but diversity of generation fuel must be maintained. Future energy policies must be formulated with consideration that approximately 14 GW of coal generation in Pennsylvania Jersey Maryland Regional Transmission Organization’s control area available during the polar vortex will be retired by 2015 and replaced with plants that utilize fuel types other than coal.