With the development of the society, the requirements for the quality of energy and power supply as well as safety and reliability are becoming higher and higher. The traditional power supply mode of large power grid is no longer meet this requirement because of its own defects. Micro grid, a new type of power grid which can integrate distributed generation is coming. It can save investment, reduce energy consumption, improve system security and flexibility, and it is the future for grid. Capacitor plays a very important role as an essential energy storage system in Microgrid. As a new type of energy storage device, super capacitor has become one of the preferred devices for energy storage in Microgrid with its irreplaceable advantages.
1. Short term power supply
There are two typical operation modes of Microgrid: under normal conditions, Microgrid is connected with conventional distribution network, which is called grid connected operation mode; When grid fail or power quality does not meet the requirements, the Microgrid will be timely disconnected from the grid to operate independently, which is called isolated grid operation mode. Microgrid often needs to absorb part of the active power from the conventional distribution network, so there will be a power shortage when the Microgrid changes from the grid connected mode to the isolated grid mode. The installation of energy storage equipment is conducive to the smooth transition of the two modes.
2. Used as energy buffer
Due to the small scale of Microgrid and small system inertia, frequent fluctuation of network and load is very serious, which affects the stable operation of the whole Microgrid. The load of Microgrid will fluctuate with the weather. In order to meet the peak load power supply, it is necessary to use fuel oil and gas to adjust the peak load. This mode of operation is too expensive because of the high price of fuel. The super capacitor energy storage system can effectively solve this problem. It can store the surplus energy of the power supply when the load is low, and feed back to the Microgrid to adjust the power demand during the peak load. It’s high power density and high energy density make it a very good choice to deal with the peak load, and the super capacitor only needs to store the energy equivalent to the peak load.
3. Improving power quality of Microgrid
Energy storage system plays a very important role in improving the power quality of Microgrid. The reactive power and active power provided by the super capacitor energy storage system can be adjusted to improve the power quality through inverter control unit. Super capacitor can quickly absorb and release high power electric energy, it is very suitable to be applied to the power quality regulation device of Microgrid to solve some transient problems, such as instantaneous power failure, voltage surge and voltage sag caused by system fault. At this time, super capacitor is used to provide fast power buffer, absorb or supplement electric energy, and provide power supply Power support is used to compensate active or reactive power to stabilize and smooth the fluctuation of grid voltage.
4. Super capacitor is essential for distributed smart grid system
We can see smart grid system will be the mainstream of future power grid system from the development trend of it. In order to build the construction of distributed smart grid system, it is necessary to have distributed energy storage device and central energy storage device and other buffer equipment. In the case of unstable energy generation process, a buffer is needed to store energy. When the process of energy generation is stable and the demand is constantly changing, energy storage devices are also needed. Fuel cell is different with wind or solar energy. As long as there is fuel, it can continuously output stable electric energy. However, the load demand varies greatly over time. If there is no energy storage device, the fuel cell will have to be very large to meet the peak energy demand, and the cost is too high. By storing the excess energy in the energy storage device, the peak energy required can be provided by the energy storage device in a short time.
In distributed grid system, the transient impact of power system is inevitable, and the superior performance of super capacitor can reduce the impact of transient impact on the whole system performance. Therefore, in the future distributed smart grid system, super capacitor bank energy storage system is essential.
