The access of distributed power sources has a profound impact on the power grid, which brings new challenges to the operation, control and protection of the power distribution network. Extensive and in-depth research was carried out. Among them, the three countries and regions of the United States, Europe and Japan are the most advanced in this technology field.
At the heart of European energy policy is the development of sustainable, competitive and secure energy. In recent years, European countries have paid more and more attention to the research of microgrid, and many countries have carried out many cooperation and discussions. The main consideration for the research and development of microgrids in Europe is to meet the user’s requirements for power quality, grid stability and environmental protection. All microgrid research plans revolve around reliability, accessibility, and flexibility. consider. The intelligentization of the power grid and the diversification of energy utilization will be the important features of the future power grid in Europe.
The EU has funded a number of scientific research projects in the 5th, 6th, and 7th framework plans. The participants include universities, manufacturers (ABB, Siemens, etc.), and power companies. The research covers many aspects of distributed power supply. The European Union’s 5th Framework Program (5th FP) has earmarked €4.5 million to fund microgrid research projects. The project has been completed and yielded some instructive research results, such as models of DERs, static and dynamic simulation tools for low-voltage asymmetric microgrids for inverter control, operational concepts of islands and interconnections, agent-based Control strategy, local black-start strategy, grounding and protection scheme, quantitative analysis of reliability, theoretical verification of laboratory microgrid platform, etc.
The EU’s 6th Framework Program (6th FP) continued to fund 4 distributed power supply projects with a funding of 8.5 million euros. At present, this plan has just ended. It evaluates and analyzes the existing distributed power generation and energy storage technologies, and formulates a future evaluation plan; conducts research on the grid-connected policies and management of distributed power generation in member states, and proposes improvement plans; It proposes solutions to the security and stability problems brought by distributed power sources to the distribution network, and proposes appropriate standards, policies and business models to promote the application of distributed power sources in European power grids; Standard formulation and equipment testing work. The microgrid-related projects in the EU 5th and 6th framework research projects mainly include:
1) MICROGRIDS
The project proposes the concept of “micro-grid”, trying to connect the distributed power to the grid in the form of “micro-grid” and connect it to the grid to support each other with the power grid to give full play to the best performance of the distributed power. The participants of the project include the French EDF Power Company, PPC Power Company in Greece, EDP Power Company in Portugal, Manufacturers, Universities. The project achieved the following results: distributed power model and steady-state and transient analysis tools for simulating unbalanced operation of microgrids dominated by low-voltage inverters; islanding and grid-connected operation mechanisms; including hierarchical algorithms and distributed Algorithmic control algorithms; local black-start technology; distributed power interface response and functional requirements; grounding and protection schemes; quantitative analysis methods for reliability benefits; multiple laboratory microgrids with different structures and functions.
2) MORE MIGROGRIDS (funded by EU 6th Framework Programme)
Continuing research on microgrids, the project’s participants include power companies from Denmark, Germany, Portugal, the Netherlands, and Poland. Research contents include: distributed power controller; development of new control strategies using next-generation information and communication technology; development of new methods for microgrid design, research on modern protection technology, solid-state switching, and inter-frequency microgrid operation technology; multi-microgrid Convergence of business and technology and the operation of decentralized electricity markets and additional service markets; development of standards for microgrid islanding and grid-connected operation; microgrid impacts on the power system, including measuring the impact of microgrids on regional, national and EU levels Quantitative methods of benefits in terms of reliability, loss, and environment; discussing the impact of microgrids on the development of grid infrastructure; microgrid pilot projects and field tests.
3) CRISP: This project studies the application of information and communication technology in distributed power grids with high penetration.
4) DGFACTS: This project focuses on solving the power quality problems caused by the connection of a large number of distributed power sources to the grid.
5) ENIRDNET: This project seeks to promote the connection of distributed power to the grid in Europe.
6) INVESTIRE: This project analyzes and evaluates existing energy storage technologies for distributed power generation, and formulates future R&D plans.
7) DG GRID: This project investigates the grid-connected policies and management of distributed power in new EU member states.
8) SOLID-DER: This project focuses on solving the security and stability problems brought by distributed power to the transmission and distribution network, and proposes appropriate standards, policies and business models to promote the use of distributed power in European power grids.
9) DERlab: This project works on the design of distributed power access system, formulation of relevant standards and equipment testing.
Various European institutions have also given different explanations for what a microgrid is. The European Commission Project Microgrids defines microgrids as: the use of primary energy and the use of micro power supplies, which can be divided into three types: uncontrollable, partially controllable and fully controlled, and can provide combined cooling, heating and electricity. Equipped with energy storage device, using power electronics for energy regulation.
From the perspective of reliability, the United Kingdom regards the microgrid as a part of the system. It has the advantages of flexibility and dispatchability and can provide strong support to the main grid in a timely manner. The difference between the scale system and the traditional power system is that the main provider of its power is the controllable micro power supply, and these micro power supplies may become loads in addition to meeting the load demand and maintaining power balance.
At the same time as the research, some European countries have built a number of microgrid pilot projects. The typical projects mainly include:
1) Greece, Kythnos Islands Microgrid project. It provides electricity for 12 households on the island, connected to the 380V distribution network, including 6 photovoltaic power generation units with a total of 11kW, a 5kW diesel engine, and a 3.3kW/50kW·h battery/inverter system. At present, it can only operate independently, and the research goal is to control the operation of microgrid to improve the system’s ability to meet peak load and improve reliability. Funded and run by ISET, Municipality of Kythnos and CRES.
2) Netherlands, Continuon’s MV/LV facility project. For resorts, there are a total of four 380V feeders, each about 400m long. Mainly photovoltaic power generation, a total of 315kW photovoltaic power generation units are installed. It can be run independently or connected to the grid. It is mainly used to test the independent operation performance of microgrids containing battery energy storage systems. Funded and run by Germanos EMforce.
3) Spain, Labein microgrid project. Access to 380V distribution network, connected to 30kV medium voltage network through two 1 000kVA and 451kVA transformers, 0.6kW and 1.6kW single-phase photovoltaic (PV), 3.6kW three-phase PV, 2 55kW diesel engines, 50kW micro gas turbines, 6kW wind turbine; 250kVA flywheel energy storage, 2.18MJ super capacitor, 1 120Ah and 1925Ah battery energy storage; 55kW and 150kW resistive loads, 2 36kVA inductive loads. It can be run independently or connected to the grid. For testing centralized and decentralized control and energy trading in electricity markets during grid-connected operation. Funded and run by 1a-bein Tecnalia.
4) Portugal, EDP’s Microgeneration facility project. The natural gas station grid connected to the 380V low-voltage network has an 80kw micro-turbine, and the excess power can be sent to the 10kV medium-voltage grid, or to the local low-voltage rural grid (3.45~41.5kVA), which can be connected to the grid or run independently. Funding and operating agency is EDP.
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