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- Overvoltage protection for grid-connected picohydro generation using photovoltaic invertersPublication . Scotta, Isabella Cristina; Maidana, Wellington; Leite, VicenteVery small-scale hydropower plants are environmentally friendly and renewable resource-based innovative solutions. The interest in pico-hydro systems (up to 5 kW) has increased significantly from the first stand-alone applications, at remote sites, to the distributed generation, with the injection of generated energy into the grid. Recently, there have been advances in the grid connection of these systems using off-the-shelf components, namely photovoltaic inverters. Therefore, pico-hydro systems have gained an enormous potential in distributed generation, particularly in the context of microgrids. However, in situations of over-power, or whenever the generator is under no load, e.g. when the grid fails, there is a need for effective over-voltage protection, as in small wind turbines. This paper proposes two over-voltage protection circuits, designed to ensure the integration of pico-hydro turbines connected to the grid using conventional photovoltaic microinverters and string inverters, for power ranges of 300 W and some kW, respectively. Extensive tests were performed on an emulation platform and a workbench using these two different over-voltage protection circuits. One is designed to connect the generators of water wheels to the grid and the other to connect 1,500 W generators of water turbines. The experimental results demonstrated the performance of the proposed over-voltage protection circuits in four different situations. Both avoid irreversible damages of generators, photovoltaic microinverters and string inverters in the context of the above-described grid connection approach.
- Pico-hydro systems: microgrid-connection approachesPublication . Leite, V.; Ferreira, Ângela P.; Couto, José; Batista, JoséSmall hydropower systems are considered an environmentally friendly energy option. They have a huge untapped potential which allows them to make a more significant contribution to future energy demand with many advantages. The integration of pico-hydro systems into microgrids is an emerging solution for the electrification of remote areas and for self-sustainable power systems. This paper presents and discusses the three main grid connection approaches for pico-hydro systems focused on the integration in small microgrids: using specifically designed power converters, using standard wind inverters and using standard photovoltaic inverters. These latest approaches based on conventional inverters are able to explore a large amount of feasible sites with low-head and very low-head. They improve efficiencies, reduce costs and environmental impacts and improve reliability. Experimental evaluation of the performance in steady-state and in dynamic conditions proves the feasibility of these innovative approaches.
- Design of a smart microgrid with small-scale hydro generation: a practical case studyPublication . Leite, VicenteMicrogrids are local electric grids integrating distributed generation and consumption, energy storage and management and power control. They can be an alternative for the energy supply of a house, a building, a small village or a wider region. Small-scale hydropower, in the range of 5 kW, consists of distributed generation systems gaining increasing interest. These so-called pico-hydro systems are becoming popular since they can take advantage of the integration of low-power wind generators and photovoltaic (PV) inverters, which are widely available at competitive prices. Thus, pico-hydro systems are not only relevant for energy generation in off-grid systems in remote areas but also for new contexts where the utility grid is available. This paper presents the design of a smart microgrid with small-scale hydro generation. It is a practical case study with the integration of two grid-connected pico-hydro turbines: a low-head propeller turbine and a water wheel. The microgrid was designed and implemented in a small museum: Casa da Seda (House of Silk). The energy generation is based on the complementarity between hydro and PV. The microgrid can operate in both grid-connected and islanded modes and feeds the House of Silk loads. The connection of both pico-hydro turbines into the microgrid is based on the integration of wind generators and PV inverters.
- Bidirectional vehicle-to-grid interface under a microgrid projectPublication . Leite, Vicente; Ferreira, Ângela P.; Batista, JoséIn the emergent deployment of smart grids, storage systems play an important role into assets utilization optimization, providing backup power and peak-shaving. This concept becomes more critical in the context of microgrids with a high penetration of renewable energy resources. Plug-in electric vehicles provide an enormous distributed storage capability, which favours the technical and economical exploitation of such systems. This paper presents a comprehensive implementation and control of a bidirectional power converter for vehicle-to-grid integration, based on a bidirectional DC/DC converter followed by a full bridge DC/AC converter.
- Analysis of the operation of a microgrid with renewable distributed generationPublication . Leite, Vicente; Ferreira, Ângela P.; Batista, José; Couto, JoséThis article reports the ongoing research on the performance assessment of an experimental microgrid which integrates various renewable energy sources. The microgrid is based on a modular commercial solution, up to a rated power of 5 kW, integrating storage devices, a backup diesel generator and various renewable energy sources and also distributed energy sources developed under ongoing R&D projects, such as the integration of a pico hydropower plant with an interface able to perform power factor compensation of the microgrid, which is introduced briefly. The performance assessment of this microgrid is conducted through a characterization of different operational states and also a preliminary energy balance of the microgrid during a time span of 4 days.
- Implementation of a smart microgrid in a small museum: the silk housePublication . Figueiredo, Luís Guilherme Aguiar; Maidana, Wellington; Leite, V.Microgrids are an alternative approach for the supply of energy integrating decentralized power sources, electrical loads, energy storage, and management in a local grid. The system has the capability of power control and energy management using communications’ network between all devices, and is known as smart microgrid. This paper presents the implementation of a smart microgrid in the Silk House, a museum dedicated to dissemination of science located in Bragança, Portugal. It was funded by the Foundation for Science and Technology of Portugal under the SilkHouse Project. The goal is to transform the House of Silk in a self-sustainable museum contributing to the dissemination of renewable sources and new technologies for future buildings in smart cities. This work presents the context and requirements for the microgrid and describes the implementation of the renewable sources (photovoltaic and pico-hydro) and the SMA Flexible Storage System based on Sunny Island and Sunny Home Manager. This work also presents and analysis the first operating results since the start of operation at the end of July 2019.
- Bidirectional vehicle-to-grid interface under a microgrid projectPublication . Leite, Vicente; Ferreira, Ângela P.; Batista, JoséIn the emergent deployment of the smart grids, storage systems play an important role into assets utilization optimization, providing backup power and peak-shaving. This concept becomes more critical in the context of microgrids with a high penetration of renewable energy resources. Plug-in electric vehicles provide an enormous distributed storage capability, which favours the technical and economical exploitation of such systems. This paper presents a comprehensive implementation and control of a bidirectional power converter for vehicle-to-grid integration, based on a bidirectional DC/DC converter followed by a full bridge DC/AC converter. The evaluation of the adopted topology and its control is performed through simulation and experimental validation. © 2014 IEEE.
- Improving the storage capability of a microgrid with a vehicle-to-grid interfacePublication . Leite, V.; Ferreira, Ângela P.; Batista, JoséIn the emergent deployment of microgrids, storage systems play an important role providing ancillary services, such as backup power and reactive power support. This concept becomes crucial in the context of microgrids with a high penetration of renewable energy resources, where storage systems may be used to smooth the intermittency and variability of most of them. Plug-in electric vehicles provide an enormous distributed storage capability, which favours the technical and economical exploitation of such systems. This paper presents a comprehensive implementation and control of a bidirectional power converter for Vehicle-to-Grid integration, based on a bidirectional DC/DC converter followed by a full bridge DC/AC converter. The evaluation of the adopted topology and its control is performed through MATLAB/Simulink simulation.
- On the implementation of a microgrid project with renewable distributed generationPublication . Leite, V.; Ferreira, Ângela P.; Batista, JoséThis paper describes the on-going implementation of a microgrid project with renewable distributed generation under the context of an initiative with demonstration purposes in an university campus. In the actual context of the electrical energy demand increase and limited conventional resources, along with the consciousness of the climate changes and the need to invest in clean energies, microgrids allows the integration of dispersed energy sources, mainly renewable, which make them cost effective, providing a viable alternative to centralized production, transmission and distribution system for remote community areas. The design concept of the microgrid and a description of the base equipment and energy sources already integrated are presented. From the on-going projects to be integrated on the microgrid, it is presented the Grid-to- Vehicle and Vehicle-to-Grid concept, which will provide a second energy storage element using the battery of an electric vehicle. To accomplish this objective, a bi-directional power converter is being developed and simulation results of its power structure and control are presented.
- Over-voltage protection for pico-hydro generation using PV microinvertersPublication . Scotta, Isabella Cristina; Ribeiro, Gabriela Moreira; Maidana, Wellington; Leite, V.Innovative, low-cost, environmentally friendly and renewable resource-based solutions are emerging to meet growing global energy demand. Hydroelectric technology is quite old and mature. Despite its importance, it is associated with large plants, with environmental impact. On contrary, small-scale systems, called pico-hydro systems (up to 5 kW) are not yet explored. Anyway, the exploration of pico-hydro systems has been increasing consistently, from the first off-grid applications in remote places to distributed generation, with the injection of the generated energy in the main grid or microgrids. Very recently, there have been advances in grid connection of these small-scale systems, using off-the-shelf components. Indeed, pico-hydro systems can be connected to the grid using off-the-shelf components, namely photovoltaic inverters. Thus, grid-connected pico-hydro systems have gained an enormous potential in distributed production. However, in situations of over-power, or whenever the generator is under no load, there is a need for effective over-voltage protection, unlike photovoltaic systems. The goal of this paper is to propose an over-voltage protection circuit, designed to ensure the integration of low-power pico-hydro systems connected to the grid using conventional photovoltaic microinverters. Extensive tests were performed on an experimental platform using three microinverters easily found on the market and a low power generator (300 W) developed for small wind turbines. The experimental results, demonstrated the performance of the proposed over-voltage protection circuit in four different situations, presented in this work, thus avoiding irreversible damages of generators and microinverters, in the context of the above described grid connection approach.