Design and experimental implementation of a hysteresis algorithm to optimize the maximum power point extracted from a photovoltaic system

In the several last years, numerous Maximum Power Point Tracking (MPPT) methods for photovoltaic (PV) systems have been proposed. An MPPT strategy is necessary to ensure the maximum power efficiency provided to the load from a PV module that is subject to external environmental perturbations such as radiance, temperature and partial shading. In this paper, a new MPPT technique is presented. Our approach has the novelty that it is a MPPT algorithm with a dynamic hysteresis model incorporated. One of the most cited Maximum Power Point Tracking methods is the Perturb and Observer algorithm since it is easily implemented. A comparison between the approach presented in this paper and the known Perturb and Observer method is evaluated. Moreover, a new PV-system platform was properly designed by employing low cost electronics, which may serve as an academical platform for further research and developments. This platform is used to show that the proposed algorithm is more efficient than the standard Perturb and Observer method.Peer ReviewedPostprint (published version

A comprehensive review of electricity storage applications in island systems

Electricity storage is crucial for power systems to achieve higher levels of renewable energy penetration. This is especially significant for non-interconnected island (NII) systems, which are electrically isolated and vulnerable to the fluctuations of intermittent renewable generation. This paper comprehensively reviews existing literature on electricity storage in island systems, documenting relevant storage applications worldwide and emphasizing the role of storage in transitioning NII towards a fossil-fuel-independent electricity sector. On this topic, the literature review indicates that the implementation of storage is a prerequisite for attaining renewable penetration rates of over 50% due to the amplified requirements for system flexibility and renewable energy arbitrage. The analysis also identifies potential storage services and classifies applicable storage architectures for islands. Amongst the available storage designs, two have emerged as particularly important for further investigation; standalone, centrally managed storage stations and storage combined with renewables to form a hybrid plant that operates indivisibly in the market. For each design, the operating principles, remuneration schemes, investment feasibility, and applications discussed in the literature are presented in-depth, while possible implementation barriers are acknowledged. The literature on hybrid power plants mainly focuses on wind-powered pumped-hydro stations. However, recently, PV-powered battery-based hybrid plants have gained momentum due to the decreasing cost of Li-ion technology. On the other hand, standalone storage establishments rely heavily on battery technology and are mainly used to provide flexibility to the island grid. Nevertheless, these investments often suffer from insufficient remunerating frameworks, making it challenging for storage projects to be financially secure.Comment: 55 pages, 10 figure

Energy storage systems and grid code requirements for large-scale renewables integration in insular grids

This thesis addresses the topic of energy storage systems supporting increased penetration of renewables in insular systems. An overview of energy storage management, forecasting tools and demand side solutions is carried out, comparing the strategic utilization of storage and other competing strategies. Particular emphasis is given to energy storage systems on islands, as a new contribution to earlier studies, addressing their particular requirements, the most appropriate technologies and existing operating projects throughout the world. Several real-world case studies are presented and discussed in detail. Lead-acid battery design parameters are assessed for energy storage applications on insular grids, comparing different battery models. The wind curtailment mitigation effect by means of energy storage resources is also explored. Grid code requirements for large-scale integration of renewables are discussed in an island context, as another new contribution to earlier studies. The current trends on grid code formulation, towards an improved integration of distributed renewable resources in island systems, are addressed. Finally, modeling and control strategies with energy storage systems are addressed. An innovative energy management technique to be used in the day-ahead scheduling of insular systems with Vanadium Redox Flow battery is presented.Esta tese aborda a temática dos sistemas de armazenamento de energia visando o aumento da penetração de energias renováveis em sistemas insulares. Uma visão geral é apresentada acerca da gestão do armazenamento de energia, ferramentas de previsão e soluções do lado da procura de energia, comparando a utilização estratégica do armazenamento e outras estratégias concorrentes. É dada ênfase aos sistemas de armazenamento de energia em ilhas, como uma nova contribuição no estado da arte, abordando as suas necessidades específicas, as tecnologias mais adequadas e os projetos existentes e em funcionamento a nível mundial. Vários casos de estudos reais são apresentados e discutidos em detalhe. Parâmetros de projeto de baterias de chumbo-ácido são avaliados para aplicações de armazenamento de energia em redes insulares, comparando diferentes modelos de baterias. O efeito de redução do potencial de desperdício de energia do vento, recorrendo ao armazenamento de energia, também é perscrutado. As especificidades subjacentes aos códigos de rede para a integração em larga escala de energias renováveis são discutidas em contexto insular, sendo outra nova contribuição no estado da arte. As tendências atuais na elaboração de códigos de rede, no sentido de uma melhor integração da geração distribuída renovável em sistemas insulares, são abordadas. Finalmente, é estudada a modelação e as estratégias de controlo com sistemas de armazenamento de energia. Uma metodologia de gestão de energia inovadora é apresentada para a exploração de curto prazo de sistemas insulares com baterias de fluxo Vanádio Redox

Smart operation of transformers for sustainable electric vehicles integration and model predictive control for energy monitoring and management

The energy transmission and distribution systems existing today are stillsignificantly dependent on transformers,despite beingmore efficient and sustainable than those of decadesago. However, a large numberof power transformers alongwith other infrastructures have been in service for decades and are considered to be in their final ageing stage. Anymalfunction in the transformerscouldaffect the reliability of the entire electric network and alsohave greateconomic impact on the system.Concernsregardingurban air pollution, climate change, and the dependence on unstable and expensive supplies of fossil fuels have lead policy makers and researchers to explore alternatives to conventional fossil-fuelled internal combustion engine vehicles. One such alternative is the introduction of electric vehicles. A broad implementation of such mean of transportation could signify a drastic reduction in greenhouse gases emissions and could consequently form a compelling argument for the global efforts of meeting the emission reduction targets. In this thesis the topic of a high penetration of electric vehicles and their possible integration in insular networksis discussed. Subsequently, smart grid solutions with enabling technologies such as energy management systems and smart meters promote the vision of smart households, which also allows for active demand side in the residential sector.However, shifting loads simultaneously to lower price periods is likely to put extra stress on distribution system assets such as distribution transformers. Especially, additional new types of loads/appliances such as electric vehicles can introduce even more uncertaintyon the operation of these assets, which is an issue that needs special attention. Additionally, in order to improve the energy consumption efficiencyin a household, home energy management systems are alsoaddressed. A considerable number ofmethodologies developed are tested in severalcasestudies in order to answer the risen questions.Os sistemas de transmissão e distribuição de energia existentes hoje em dia sãosignificativamente dependentes dos transformadores, pese embora sejammais eficientes e sustentáveis do que os das décadas passadas. No entanto, uma grande parte dos transformadores ao nível dadistribuição, juntamente com outras infraestruturassubjacentes, estão em serviço há décadas e encontram-se nafasefinal do ciclo devida. Qualquer defeito no funcionamento dos transformadorespode afetara fiabilidadede toda a redeelétrica, para além de terum grande impactoeconómico no sistema.Os efeitos nefastos associadosàpoluição do arem centro urbanos, asmudançasclimáticasea dependência de fontes de energiafósseis têm levado os decisores políticos e os investigadores aexplorar alternativas para os veículos convencionais de combustão interna. Uma alternativa é a introdução de veículos elétricos. Umaampla implementação de tal meio de transporte poderia significar uma redução drástica dos gases de efeito de estufa e poderiareforçar os esforços globais para ocumprimento das metas de redução de emissõesde poluentes na atmosfera.Nesta tese é abordado o tema da elevada penetração dos veículos elétricose a sua eventual integração numarede elétricainsular. Posteriormente, são abordadas soluções de redeselétricasinteligentes com tecnologias específicas, tais como sistemas de gestão de energia e contadores inteligentes que promovamo paradigmadas casas inteligentes, que também permitem a gestão da procura ativano sector residencial.No entanto, deslastrando significativamente as cargaspara beneficiar de preçosmais reduzidosé suscetíveldecolocarconstrangimentosadicionaissobre os sistemas de distribuição, especialmentesobre ostransformadores.Osnovos tipos de cargas tais como os veículos elétricospodem introduzir ainda mais incertezassobre a operação desses ativos, sendo uma questão que suscitaespecial importância. Além disso, com ointuitode melhorar a eficiência do consumo de energia numa habitação, a gestão inteligente daenergia é um assunto que também éabordadonesta tese. Uma pletora de metodologias é desenvolvida e testadaemvários casos de estudos, a fim de responder às questões anteriormente levantadas

ENHANCING LOW VOLTAGE RIDE THROUGH CAPABILITY IN UTILITY GRID CONNECTED SINGLE PHASE SOLAR PHOTOVOLTAIC SYSTEM

The steady rise in utility grid penetration of single phase solar photovoltaic system has contributed to the mandatory requirement of Low Voltage Ridethrough (LVRT) capability. LVRT capability provides stable grid integration during transient conditions. A seamless LVRT capability operation in a single phase photovoltaic system using peak value based fault detection and Orthogonal Signal Generation (OSG) based voltage sag detection is conducted. In this paper, two controllers are employed for two different operations. The PQ theory controller is used for power control operation and Proportional–Resonant (PR) with Harmonic Compensation (HC) controller is used for current control operation in LVRT. MATLAB/Simulink verifies the LVRT operation mode as per the grid code requirements to ride through voltage sag during fault condition. It is observed that the system is in operation during transient conditions and provides reactive support to ride through the fault

micro vs MEGA: trends influencing the development of the power system

publishedVersio

Modelling and simulation of an insular grid with the presence of High Voltage Direct Current

Insular electrical grids, usually isolated from larger mainland grids, are more prone to having stability issues. These are usually weak and have limited resources in regards to power sources, which adds up with the fact that this type of grids usually lack access to the electricity market. High Voltage Direct Current (HVDC) technology presents the possibility of long distance overseas connections that alleviate the effects of these issues. Use of HVDC technology is on the rise, its main focus being long distance transport of power. Its effciency and the stability it provides to grids, paired with the aforementioned need for overseas connections and off-shore wind generation have helped it become as common as it is nowadays. The aim of this thesis is to study the behaviour of an insular grid with the presence of HVDC and the needed power converter for the HVDC connection. The behaviour of the system with and without the converter's frequency support will be analyzed. A case based on the Majorcan 220kV grid (Balearic Islands, Spain) with an HVDC connection representing a link with the mainland is used to analyze the behaviour of an insular grid with and without the frequency support. HVDC presence in the grid is represented by a converter modelled as seen in ”Active and Reactive Power Control of Grid Connected Distributed Generation Systems” [1]. The tools used for modelling and simulating are MatLab® 2015b and PSCAD 4.6 EDU. MatLab® is used for running steady state simulations of the grid's behaviour and for initial modelling of the VSC converter. For the first, the MATPOWER X.Y package is used. In regards to the former, the Simulink environment is used. PSCAD is used for dynamic analysis of the grid, with and without the power converter's grid frequency support. Comparison of the MatLab® 2015b and PSCAD 4.6 EDU simulations show that the dynamic model behaves as it is expected from it. There are no relevant differences from the dynamic and the static models' results. The study of the dynamic behaviour of the system in front of a fault shows that the HVDC connection's grid frequency support alleviates the negative impact that said events have on the grid's frequency. This is done while also reducing the amount of power that needs to be generated with the limited local resources

Mitigation of Power System Oscillation in a DFIG-Wind Integrated Grid: A Review

The continuous rise in demand for power supply has made researchers and power system engineers seek alternatives through renewable energy sources to complement the power supply in the power system grid. Wind energy conversion system (WECS) which is the means of harnessing power generation through wind is reportedly one of the most widely installed renewable alternative sources globally. Integrating WECS into the conventional power system grid results in a complex power system grid. Thus, during a disturbance or a fault period on the grid, if proper control measures are not put in place, power system instability due to power system oscillations arises. One such control measure is the damping controller which is coupled to the generating plant through its excitation system. Damping controllers help to dampen power system oscillations, but due to the dynamic nature of the power system and uncertainties inherent in a wind-integrated power grid system, fixed damping controller parameters cannot effectively dampen power system oscillations. Hence, damping controller design becomes an optimization problem. This research reviews damping controller design in a wind-integrated system using optimization techniques