Smart Micro-Grid refers to a small power distribution system consisting of distributed generators, energy storage devices, energy conversion devices, loads, monitoring and protection devices. The proposed micro grid aims at realizing the flexible and efficient application of distributed generation, and solving the large number and various forms of grid-connected distributed power supply. The development and extension of micro-grid can fully promote the large-scale access of distributed generation and renewable energy, and realize the high reliable supply of multi-energy forms. It is an effective way to realize active distribution network and make the transition from traditional grid to smart grid.
There are five kinds of micro grids in modern times:
DC micro grid: Distributed generators, energy storage devices and loads are connected to DC bus, and DC network is connected to external AC network through power electronic inverters. DC micro grid can provide power to AC and DC loads of different voltage levels through power electronic conversion devices, and the fluctuation of distributed generation and load can be regulated by energy storage devices on the DC side.
AC micro grid: Distributed power supply and energy storage devices are connected to AC bus through power electronic devices. At present, the AC micro grid is still the main form of micro grid. By controlling the switch at PCS, the grid connected operation and the landing mode transformation can be realized.
AC/DC hybrid micro grid: It contains both AC bus and DC bus, which can supply both AC load and DC load directly.
Medium-Voltage Distribution Branch Micro grid: A microgrid that integrates distributed generation and load effectively on the basis of medium-voltage distribution branch. It is suitable for supplying power to user areas with medium capacity, high reliability and concentration.
Low Voltage Micro grid: A micro grid formed by properly integrating users’distributed generators and loads at low voltage level. Most of these micro grids are owned by power or energy users, and their scale is relatively small.