The proposal of microgrid technology is closely related to the application and development of distributed generation (DG) technology. The concept of DG was first announced and officially promoted in the U.S. Public Utilities Management Policy Act of 1978, which is defined as:
1) A new power supply system that is completely different from the traditional power supply mode, in order to meet the needs of specific users or support the economic operation of the existing distribution network, it is distributed in the vicinity of users in a decentralized manner, with a power generation of several kilowatts to 50MW. Compatible independent power supply.
2) Any power generation facility installed near the user, regardless of its size and type of primary energy (including DG, combined heat and power, combined cooling, heat and power, and various energy storage technologies, etc.).
The definition of DG in the 1EEE1547.2-2008 distributed power grid access standard is more specific: distributed power generation, also known as distributed power generation, is a collective name for various power generation equipment and power conversion equipment, including such as photovoltaic arrays ( PV), wind turbines, fuel cells, micro gas turbines, traditional diesel and gas internal combustion engines, gas turbines and other power sources, as well as corresponding power converters and power storage devices.
In general, DG refers to “small power generation systems directly connected to the distribution network or user side”, while distributed power (Distributed Resource, DR) refers to distributed power generation and energy storage facilities (Energy Storage, ES) The combined system (DR=DG+ES) of distributed power generation includes natural gas (as well as coalbed methane, biogas, etc.), solar energy, biomass energy, hydrogen energy, wind energy, water energy, etc.; and energy storage facilities include Batteries, super capacitors, flywheel energy storage, etc. In addition, in order to improve energy efficiency and reduce costs, this power generation technology often adopts Combined Cooling, Heat and Power (CCHP), or Combined Heat and Power (CHP) or Cogeneration).
Compared with the traditional power supply relying on long-distance transmission and distribution, DG adapts to the decentralized power demand and resource distribution to a certain extent, and at the same time acts as a backup with the power grid, which improves the reliability of power supply; and the distributed power generation technology based on clean energy It has many advantages such as less pollution, high reliability and energy utilization efficiency, and flexible installation location. At the same time, there are also many problems in the access of distributed generation to the power grid, such as the high cost of single-unit access to distributed generation and difficulty in control. In addition, in order to reduce the impact of distributed power sources on the main power grid, large systems often adopt restrictions and isolation methods to deal with distributed power sources. IEEE 1547 stipulates that when the power system fails, distributed power sources must be immediately out of operation. This greatly limits the full effect of distributed power generation, and indirectly limits the use of clean energy.
In order to coordinate the contradiction between the power grid and distributed power sources, solve the impact on the power grid and users caused by the simple grid-connected operation of a large number of distributed power sources with scattered locations, various forms and different characteristics, and reduce their access to power quality, system protection, system Operation and other adverse effects, to fully exploit the value and benefits of distributed power to the grid and users, scholars put forward the concept of microgrid (Microgrid). Microgrid can be regarded as a system composed of distributed power sources, loads, energy storage and control devices. It behaves as a single controllable unit to the grid and can respond to central control signals.
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