This article presents the demonstrative development of the Towards Intelligent DC-based hybrid Grids Optimizing the Network performance (TIGON) project at the Centre for the Development of Renewable Energy - Centre for Energy, Environmental and Technological Research (CE.D.E.R.-CIEMAT), as well as the established objectives to be achieved with the implementation of a microgrid with smart grid architecture based on direct current (DC) and integrated into the current energy system. This type of architecture is proposed as a future solution to reduce energy losses caused by DC-alternating current (AC) conversions, increasing the overall performance and profitability of hybrid grids. All this without forgetting to ensure the supply, stability and reliability of the system with the development of all the necessary equipment and protections to make this approach a reality. The microgrid design and process of implementation start from a transformation centre, from which the medium voltage direct current (MVDC) grid will be created by the Solid State Transformer (SST). In the MVDC grid, we will find a bank of lead-acid batteries and other essential equipment in the microgrid, a DC/DC converter that will create the low voltage direct current (LVDC) grid. On the LVDC side, several branches have been designed to connect the rest of the systems; generation (mini-wind and photovoltaic), storage (LFP batteries) and loads (AC and DC loads). Each of the equipment will have a connection to the DC grid through converters made exclusively for this equipment and connexion to the AC grid, which will allow us to obtain all the necessary data to carry out the required studies to achieve the established objectives of the project.
Keywords: DC microgrid; DC/AC conversion; DC/DC converter; Hybrid microgrid; LVDC (low voltage DC); MVDC (medium voltage DC); direct current (DC).
Most of the current electrical grid infrastructure is based on alternating current (AC) because the facilities used for long distance power distribution are made to operate in AC. The reason behind this is that power losses are less at high voltage AC. However, in recent years, renewable energies, local generation and consumption are being promoted 1, which is leading to an important energy transition for all citizens. This transition also derives from the type of current generated from renewable energy sources (such as solar or wind power, these being the most widespread technologies), as the vast majority of them generate energy in direct current (DC) 2. In addition, it is common to find storage systems associated with these renewable energy sources, due to their variability linked to weather conditions. These storage systems also operate in DC. Finally, to close the generation, storage and consumption cycle, part of the consumption with devices used on daily basis is carried out in DC, such as LED lighting, computers or mobile phones use DC for their operation. Other examples include charging stations for electric vehicles, which are becoming more and more widespread, and the electric railway system 3, 4. This implies achieving conversions in current types resulting in losses linked to these changes 5– 8 and thus reducing the amount of energy reaching the consumer versus the amount of energy produced. TIGON project seeks to facilitate this transition and bring it to reality by generating equipment, allowing the transition to DC, and by reducing AC consumption. It therefore benefits us as consumers, thanks to the reduction of energy conversion losses associated with the transformation from AC to DC. CE.D.E.R.-CIEMAT, as a demonstration centre for the project, will have a DC-based hybrid microgrid where this idea can be integrated and operated in a real location.
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