At present, China’s power system is mostly a centralized single power supply system with large generating units, large power grids, and high voltage as the main characteristics. However, with the increasing scale of power grids and the demands of economic development, loads have higher and higher requirements for power supply reliability and power quality. Several large-scale power outages around the world have exposed the shortcomings of large-scale centralized power supply methods. At the same time, the global energy crisis and environmental pollution issues have also prompted the development and utilization of new energy sources to become an urgent need. Therefore, in order to make up for and perfect the disadvantages of large-scale centralized power systems such as difficulty in operation and serious environmental pollution, distributed generation (DG), because of its small investment, the use of clean and renewable energy, the ability to complement multiple resources and regions, and to improve the reliability and flexibility of power supply, it has received extensive attention. At present, the organic combination and good complementarity of distributed power generation with large power grids has become an important development direction of the power industry and energy industry in the new century.
So far, there is no uniform and strict definition of distributed generation (DG). Due to the different policies and understanding of different countries, the names are also different. Generally speaking, distributed power generation refers to small, modular, decentralized power generation units with power generation from several kilowatts to tens of megawatts, and are arranged near users. The definition of distributed power generation in Q/GDW11147-2013 “Code for Design of Distributed Power Supply Access to Distribution Networks” is as follows: Distributed Power Generation (DG) refers to the construction, installation, and operation of power generation facilities at or near the site where the user is located, with spontaneous self-use by the user, surplus electricity being used for the Internet, and the balance adjustment of the distribution network system as a feature of power generation facilities or integrated cascade utilization of multi-generation facilities with power output.
Compared with the conventional centralized large-scale grid power supply, the distributed power generation system has the following characteristics:
(1) The installed capacity is small. The single unit capacity and power generation scale of distributed power generation systems are generally not large, usually below 50MW. Therefore, there is no need to build large-scale power plants, substations and distribution stations, and its construction period is short, the area is small, and the initial investment is small. However, distributed power generation systems often lack scale benefits, and the cost per unit capacity is much higher than that of centralized large-scale generating units.
(2) Close to the user and use it on the spot. Distributed power generation systems are usually installed near the power user side, directly connected to the medium and low voltage distribution network, and supply power to the load nearby. Therefore, there is no need for long-distance transmission lines, which reduces transmission and distribution losses, and there is no need to occupy a large amount of land and space to build transmission corridors, and the construction is simple and cheap. The electromagnetic radiation produced by it is also far lower than the conventional centralized power generation method.
(3) The types of power generation are mainly renewable energy power generation, comprehensive resource utilization power generation, etc. Distributed power generation systems mostly use clean and renewable energy, such as wind energy, solar energy, biomass energy, and geothermal energy. Compared with fossil energy, it can effectively reduce carbon dioxide emissions and achieve environmental benefits while supplying power. In addition, these energy sources are difficult to use with conventional centralized power supply due to their low energy density and dispersion. Distributed power generation has opened up a new direction for the use of renewable energy. In addition, distributed power generation can be combined with cogeneration of cooling, heating and power, using waste heat, pressure, and combustible waste gas to generate electricity in accordance with local conditions. Or use the waste heat of power generation for heating and cooling. Through the organic integration of different cycles, it can meet the diverse needs of users while realizing the comprehensive cascade utilization of energy, which has good energy-saving effects, and its energy utilization rate can reach more than 80%.
(4) Flexible operation to meet the needs of special occasions. For some remote agricultural and pastoral areas, mountainous areas or islands, it takes huge investment and a long time period to form a large-scale and powerful centralized power supply and distribution network. In these areas, distributed power generation can be used independently to supply power to users to solve the problem of power shortage. For important loads, the combined power supply method of distributed power generation and the large power grid can be used to maintain the power supply of important users in the event of grid collapse and accidental disasters (such as snowstorms, earthquakes, wars, and man-made damage), which greatly improves the reliability of power supply. In addition, for peak power periods, distributed power generation can also be used to provide part of the power to reduce the power supply pressure on the grid. In addition, the distributed power generation system can also reduce or ease the construction and transformation of large-scale power plants and power grids, saving economic investment.