Distributed power system grid connection technical requirements and development status. At present, although my country's electricity supply is in a state of oversupply, its power supply structure is not very reasonable and seriously harms the ecological environment. Distributed power system refers to a power generation facility or energy comprehensive with power output that is constructed and installed at or near the user's site, and is operated mainly for self-use on the user's side, with excess electricity connected to the grid, and balanced adjustment of the distribution network system. The cascade utilizes polygeneration facilities.

　　Distributed power system grid connection technical requirements

　　Distributed power system grid connection technology refers to the technical measures for connecting distributed power sources to the distribution network and ensuring the safe and reliable operation of the distribution network containing distributed power sources and qualified power quality. The access to distributed power systems makes the distribution network an active network with two-way power flow. It also brings about technical problems such as voltage fluctuations and relay protection malfunction or refusal to operate. The impact of distributed power supply access on distribution network, active distribution network planning, distributed power grid connection protection and control, active distribution network protection, active distribution network voltage control, active distribution network power quality Control, distributed power supply dispatching and management, etc., are hot topics in power technology research.

　　Recently, the full text of the National Standards Committee's "Technical Requirements for Distributed Power Supply Grid Connection" was officially released, and the relevant standards will be implemented on December 1, 2017. The standard stipulates the general principles and technical requirements that should be followed in the design, construction and operation of distributed power systems connected to the power grid.

　　1) UK. The UK currently mainly has BSEN50438:2007 technical requirements for micro power generation equipment to be connected to low-voltage distribution grids and standards for embedded power plants to be connected to public distribution grids. Among them, the micro power supply targeted by the British BSEN50438:2007 standard is a distributed power supply connected to a 230,400V distribution network with a single-phase current not exceeding 16A;

　　2)Germany. In January 2008 and August 2011, Germany issued guidelines for the connection of power plants to the medium-voltage power grid and guidelines for the connection of power generation systems to the low-voltage distribution grid. Both guidelines took into account the connection of renewable energy power generation. It is suitable for wind power, hydropower, combined power generation systems (such as biomass energy, biogas or natural gas thermal power generation systems, etc.), photovoltaic power generation systems and other power generation systems that are connected to the medium and low voltage power grid through synchronous motors, asynchronous motors or converters.

　　3) Canada. Canada currently has 2 major interconnection standards, including the C22.2N0.257 inverter-based micropower distribution network interconnection standard and the C22.3N0.9 distributed power supply system interconnection standard}s}, of which C22.2N0. The 257 standard stipulates the interconnection requirements between inverter-based distributed power supplies and low-voltage distribution grids below 0.6kV. C22.3N0.9 is suitable for distributed power systems connected to distribution grids below 50kV and with grid-connected capacity not exceeding 10MW. .

　　4)China. In 2010 and 2011, the State Grid Corporation of China issued Q/GDW480-2010 Technical Regulations for the Integration of Distributed Power Sources into the Power Grid, Q/GDW666-2011 Technical Specifications for Testing of Distributed Power Sources Connected to the Distribution Network, and Q/GDW667-2011 Distributed Power Sources. There are 4 enterprise standards including the operation control specification for power supply access to distribution network and the Q/GDW677-2011 functional specification for distributed power supply system access to distribution network monitoring system.

　　In addition to unified standards for various types of distributed power systems, the IEC and many countries have also issued some grid connection standards for specific distributed power forms, such as wind power grid connection guidelines.

　　Current status of grid-connected development of distributed power systems

　　In recent years, renewable energy has become the fastest growing energy type. According to relevant reports, it is estimated that renewable energy will account for more than 50% of all electricity in 2050, including distributed energy generation technologies such as photovoltaic and wind power, and the integration of different energy sources. Integrated solutions will occupy a major position in the energy structure. Distributed power systems are distributed at multiple points and are close to demand centers, which can promote the efficient use of renewable energy and become an important development trend of modern power systems.

　　With the rapid development of distributed power generation technology and the guidance and support of relevant national policies, the penetration rate of distributed power systems in the distribution network will gradually increase. However, due to the low voltage level of the traditional distribution network, weak grid structure, insufficient adjustment capabilities, and the intermittency and volatility of distributed power sources such as high-penetration photovoltaics and wind power, the voltage, power, and frequency fluctuations of the distribution network are more severe. Severely reducing the power quality and operational safety and reliability of the power system.

　　The integration of distributed power systems into the grid has transformed the traditional passive distribution network into an active distribution network, changing the flow of power in the system and causing reverse power transmission. This has subverted the theoretical basis of the existing radial distribution network and has a negative impact on the existing radial distribution network. The protection facilities of distribution networks pose huge challenges. With the economic development and industrial upgrading of our country, the existing power distribution and transformation equipment capacity will not be able to meet the increasing high load demand. High-tech industries such as advanced manufacturing and financial systems have also put forward higher requirements for power supply reliability and power quality. .

　　The impact of distributed power system grid connection on power quality

　　In recent years, distributed power generation technology represented by wind power generation and photovoltaic power generation has been rapidly developed and vigorously promoted. On the one hand, the environmental friendliness and recyclability of distributed power systems provide help in coping with the energy crisis and environmental pollution; on the other hand, people have also noticed that the output power of distributed power generation has a strong impact due to limitations of natural conditions. The randomness and volatility of large-scale distributed power sources integrated into the power grid will have a serious impact on the power supply quality of the existing power system.

　　At present, the capacity of distributed power systems is relatively small. Under the existing installed capacity, distributed power will not have an impact on the large power grid system. However, with the development of distributed power, if the number of such small units reaches a certain level, , it may affect the characteristics of the entire power system.

　　Distributed power grid-connected operation currently mainly occurs in distribution networks, and its impact on power quality is manifested in two aspects: impact on voltage fluctuations and harmonic problems.

　　The above are the technical requirements and development status of grid-connected distributed power systems. The distributed power system is such a small and medium-sized device that converts renewable energy such as wind energy and solar energy into electrical energy, which is very consistent with the development of the power industry. It is of great significance to analyze the way distributed power is connected to the grid and its impact on power supply reliability!

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