Estudo sobre a interação de métodos anti-ilhamento para sistemas fotovoltaicos conectados à rede de distribuição de baixa tensão com múltiplos inversores.

Este trabalho estuda a interação entre os métodos anti-ilhamento aplicados em sistemas fotovoltaicos residenciais, operando simultaneamente em uma rede de distribuição de baixa tensão. Os sistemas fotovoltaicos em geral interagem entre si, com a rede de distribuição da concessionária e com outras fontes de geração distribuída. Uma consequência importante dessa interação é a ocorrência do ilhamento, que acontece quando as fontes de geração distribuída fornecem energia ao sistema elétrico de potência mesmo quando esta se encontra eletricamente isolada do sistema elétrico principal. A função anti-ilhamento é uma proteção extremamente importante, devendo estar presente em todos os sistemas de geração distribuída. Atualmente, são encontradas diversas técnicas na literatura. Muitas delas oferecem proteção adequada quando um inversor está conectado à linha de distribuição, mas podem falhar quando dois ou mais funcionam simultaneamente, conectados juntos ou próximos entre si. Dois destes métodos são analisados detalhadamente nesse estudo, avaliados em uma rede de distribuição residencial de baixa tensão. Os resultados obtidos mostram que a influência de um método sobre o outro é dependente da predominância de cada um deles dentro do sistema elétrico. Contudo, nas condições analisadas o ilhamento foi detectado dentro do limite máximo estabelecido pelas normas pertinentes.

Impacts of distributed generation on low-voltage distribution network protection

This paper reports work of a MEng student final year project, which looks in detail at the impacts that distributed generation can have on existing low-voltage distribution network protection systems. After a review of up-to-date protection issues, this paper will investigate several key issues that face distributed generation connections when it comes to network protection systems. These issues include, the blinding of protection systems, failure to automatically reclose, unintentional islanding, loss of mains power and the false tripping of feeders. Each of these problems impacts on protection systems in its own way. This study aims to review and investigate these problems via simulation demonstrations on one representative network to recommend solutions to practices.

Hybrid Power System Intelligent Operation and Protection Involving Plug-in Electric Vehicles

Two key solutions to reduce the greenhouse gas emissions and increase the overall energy efficiency are to maximize the utilization of renewable energy resources (RERs) to generate energy for load consumption and to shift to low or zero emission plug-in electric vehicles (PEVs) for transportation. The present U.S. aging and overburdened power grid infrastructure is under a tremendous pressure to handle the issues involved in penetration of RERS and PEVs. The future power grid should be designed with for the effective utilization of distributed RERs and distributed generations to intelligently respond to varying customer demand including PEVs with high level of security, stability and reliability. This dissertation develops and verifies such a hybrid AC-DC power system. The system will operate in a distributed manner incorporating multiple components in both AC and DC styles and work in both grid-connected and islanding modes. The verification was performed on a laboratory-based hybrid AC-DC power system testbed as hardware/software platform. In this system, RERs emulators together with their maximum power point tracking technology and power electronics converters were designed to test different energy harvesting algorithms. The Energy storage devices including lithium-ion batteries and ultra-capacitors were used to optimize the performance of the hybrid power system. A lithium-ion battery smart energy management system with thermal and state of charge self-balancing was proposed to protect the energy storage system. A grid connected DC PEVs parking garage emulator, with five lithium-ion batteries was also designed with the smart charging functions that can emulate the future vehicle-to-grid (V2G), vehicle-to-vehicle (V2V) and vehicle-to-house (V2H) services. This includes grid voltage and frequency regulations, spinning reserves, micro grid islanding detection and energy resource support. The results show successful integration of the developed techniques for control and energy management of future hybrid AC-DC power systems with high penetration of RERs and PEVs.

Proteção em sistemas elétricos com geração distribuída utilizando a transformada wavelet

A typical electrical power system is characterized by centr alization of power gene- ration. However, with the restructuring of the electric sys tem, this topology is changing with the insertion of generators in parallel with the distri bution system (distributed gene- ration) that provides several benefits to be located near to e nergy consumers. Therefore, the integration of distributed generators, especially fro m renewable sources in the Brazi- lian system has been common every year. However, this new sys tem topology may result in new challenges in the field of the power system control, ope ration, and protection. One of the main problems related to the distributed generati on is the islanding formation, witch can result in safety risk to the people and to the power g rid. Among the several islanding protection techniques, passive techniques have low implementation cost and simplicity, requiring only voltage and current measuremen ts to detect system problems. This paper proposes a protection system based on the wavelet transform with overcur- rent and under/overvoltage functions as well as infomation of fault-induced transients in order to provide a fast detection and identification of fault s in the system. The propo- sed protection scheme was evaluated through simulation and experimental studies, with performance similar to the overcurrent and under/overvolt age conventional methods, but with the additional detection of the exact moment of the fault.

Utilização da transformada de wavelet para detecção de variações anormais de tensão em sistemas elétricos com geração distribuída

The increasing demand in electricity and decrease forecast, increasingly, of fossil fuel reserves, as well as increasing environmental concern in the use of these have generated a concern about the quality of electricity generation, making it well welcome new investments in generation through alternative, clean and renewable sources. Distributed generation is one of the main solutions for the independent and selfsufficient generating systems, such as the sugarcane industry. This sector has grown considerably, contributing expressively in the production of electricity to the distribution networks. Faced with this situation, one of the main objectives of this study is to propose the implementation of an algorithm to detect islanding disturbances in the electrical system, characterized by situations of under- or overvoltage. The algorithm should also commonly quantize the time that the system was operating in these conditions, to check the possible consequences that will be caused in the electric power system. In order to achieve this it used the technique of wavelet multiresolution analysis (AMR) for detecting the generated disorders. The data obtained can be processed so as to be used for a possible predictive maintenance in the protection equipment of electrical network, since they are prone to damage on prolonged operation under abnormal conditions of frequency and voltage.

Integración de dispositivos electrónicos inteligentes en Smart Grid

El sector eléctrico está experimentando cambios importantes tanto a nivel de gestión como a nivel de mercado. Una de las claves que están acelerando este cambio es la penetración cada vez mayor de los Sistemas de Generación Distribuida (DER), que están dando un mayor protagonismo al usuario a la hora de plantear la gestión del sistema eléctrico. La complejidad del escenario que se prevé en un futuro próximo, exige que los equipos de la red tenga la capacidad de interactuar en un sistema mucho más dinámico que en el presente, donde la interfaz de conexión deberá estar dotada de la inteligencia necesaria y capacidad de comunicación para que todo el sistema pueda ser gestionado en su conjunto de manera eficaz. En la actualidad estamos siendo testigos de la transición desde el modelo de sistema eléctrico tradicional hacia un nuevo sistema, activo e inteligente, que se conoce como Smart Grid. En esta tesis se presenta el estudio de un Dispositivo Electrónico Inteligente (IED) orientado a aportar soluciones para las necesidades que la evolución del sistema eléctrico requiere, que sea capaz de integrase en el equipamiento actual y futuro de la red, aportando funcionalidades y por tanto valor añadido a estos sistemas. Para situar las necesidades de estos IED se ha llevado a cabo un amplio estudio de antecedentes, comenzando por analizar la evolución histórica de estos sistemas, las características de la interconexión eléctrica que han de controlar, las diversas funciones y soluciones que deben aportar, llegando finalmente a una revisión del estado del arte actual. Dentro de estos antecedentes, también se lleva a cabo una revisión normativa, a nivel internacional y nacional, necesaria para situarse desde el punto de vista de los distintos requerimientos que deben cumplir estos dispositivos. A continuación se exponen las especificaciones y consideraciones necesarias para su diseño, así como su arquitectura multifuncional. En este punto del trabajo, se proponen algunos enfoques originales en el diseño, relacionados con la arquitectura del IED y cómo deben sincronizarse los datos, dependiendo de la naturaleza de los eventos y las distintas funcionalidades. El desarrollo del sistema continua con el diseño de los diferentes subsistemas que lo componen, donde se presentan algunos algoritmos novedosos, como el enfoque del sistema anti-islanding con detección múltiple ponderada. Diseñada la arquitectura y funciones del IED, se expone el desarrollo de un prototipo basado en una plataforma hardware. Para ello se analizan los requisitos necesarios que debe tener, y se justifica la elección de una plataforma embebida de altas prestaciones que incluye un procesador y una FPGA. El prototipo desarrollado se somete a un protocolo de pruebas de Clase A, según las normas IEC 61000-4-30 e IEC 62586-2, para comprobar la monitorización de parámetros. También se presentan diversas pruebas en las que se han estimado los retardos implicados en los algoritmos relacionados con las protecciones. Finalmente se comenta un escenario de prueba real, dentro del contexto de un proyecto del Plan Nacional de Investigación, donde este prototipo ha sido integrado en un inversor dotándole de la inteligencia necesaria para un futuro contexto Smart Grid.

Robust control for power sharing in microgrids with low-inertia wind and PV generators

This paper presents a robust control design scheme for a multidistributed energy resource (DER) microgrid for power sharing in both interconnected and islanded modes. The scheme is proposed for micgrogrids consisting of photovoltaic (PV) units and wind turbine driven doubly fed induction generators (DFIGs). A battery is integrated with each of the wind and solar DER units. The control scheme has two levels: 1) one centralized multi-input–multi-output robust controller for regulating the set reference active and reactive powers and 2) local real and reactive power droop con-trollers, one on each DER unit. The robust control scheme utilizes multivariable H1 control to design controllers that are robust to the changes in the network and system nonlinearities. The effectiveness of the proposed controller is demonstrated through large-distur-bance simulations, with complete nonlinear models, on a test micro-grid. It is found that the power sharing controllers provide excellent performance against large disturbances and load variations during islanding transients and interconnected operation.

Hybrid power system intelligent operation and protection involving plug-in electric vehicles

Two key solutions to reduce the greenhouse gas emissions and increase the overall energy efficiency are to maximize the utilization of renewable energy resources (RERs) to generate energy for load consumption and to shift to low or zero emission plug-in electric vehicles (PEVs) for transportation. The present U.S. aging and overburdened power grid infrastructure is under a tremendous pressure to handle the issues involved in penetration of RERS and PEVs. The future power grid should be designed with for the effective utilization of distributed RERs and distributed generations to intelligently respond to varying customer demand including PEVs with high level of security, stability and reliability. This dissertation develops and verifies such a hybrid AC-DC power system. The system will operate in a distributed manner incorporating multiple components in both AC and DC styles and work in both grid-connected and islanding modes. ^ The verification was performed on a laboratory-based hybrid AC-DC power system testbed as hardware/software platform. In this system, RERs emulators together with their maximum power point tracking technology and power electronics converters were designed to test different energy harvesting algorithms. The Energy storage devices including lithium-ion batteries and ultra-capacitors were used to optimize the performance of the hybrid power system. A lithium-ion battery smart energy management system with thermal and state of charge self-balancing was proposed to protect the energy storage system. A grid connected DC PEVs parking garage emulator, with five lithium-ion batteries was also designed with the smart charging functions that can emulate the future vehicle-to-grid (V2G), vehicle-to-vehicle (V2V) and vehicle-to-house (V2H) services. This includes grid voltage and frequency regulations, spinning reserves, micro grid islanding detection and energy resource support. ^ The results show successful integration of the developed techniques for control and energy management of future hybrid AC-DC power systems with high penetration of RERs and PEVs.^