Effective energy storage mode is of great significance to the safety and stability of the microgrid operation and the internal power supply balance. Due to the randomness and intermittent nature of the distributed unit output units such as solar photovoltaic and wind power generation in the microgrid, and the power load also has random variation characteristics, it has a great impact on the stability of the microgrid operation.
1 The role of supercapacitor and battery hybrid energy storage system in microgrid
There are two main modes of operation of the microgrid, namely, grid-connected operation and island operation. In general, the microgrid operates in parallel with the conventional distribution network. When a grid accident or power quality accident occurs, the microgrid adopts an island operation mode. During the operation of the microgrid, the conversion of these two modes of operation will be involved. During the conversion process, a certain power shortage will be caused. This requires a certain energy storage device to ensure the balanced conversion of the two operating modes of the microgrid. Stability of operation.
In some new energy power generation processes, due to external factors, there is often no phenomenon of power output. At this time, the energy storage system needs to provide power to the power users. The small size of the microgrid, weak self-regulation, load fluctuations and grid operation failures will have a great impact on it. The supercapacitor and battery hybrid energy storage system can effectively solve this problem, and can store excess electric energy when the load is low. The load peak feeds the stored electric energy to the microgrid to provide assistance for the adjustment of the microgrid power.
The supercapacitor and battery hybrid energy storage system is set in the microgrid, which can solve the problems of voltage drop and voltage drop of the microgrid, and improve the power quality of the microgrid.
2 hybrid system energy storage system
Battery storage is one of the most widely used and promising energy storage methods in microgrids. The battery is stored to solve the power demand of the system during peak load, and the battery energy storage is also used to assist the reactive power compensation device, which is beneficial to suppress voltage fluctuation and flicker. However, the charging voltage of the battery should not be too high, and the charger is required to have a voltage regulation and a voltage limiting function. The charging current of the battery should not be too large, and the charger is required to have a steady current and current limiting function, so its charging circuit is also complicated.
In addition, the charging time is long, and the number of times of charging and discharging is only several hundred times, thus limiting the service life and high maintenance cost. If it is overcharged or short-circuited, it will be more explosive than other energy storage methods. Since harmful metals such as lead are used in the battery, they also cause environmental pollution. Common storage batteries include lead-acid batteries, lithium-ion batteries, and the like. With the advancement of technology, breakthroughs have been made in the research of liquid vanadium batteries and sodium-sulfur batteries.
These two batteries have excellent characteristics such as high energy efficiency, long service life and no discharge, and are used in some foreign microgrid research systems. However, due to price reasons, large-scale use in the microgrid will take time.
Supercapacitors refer to long and short media made of special materials. Compared with ordinary capacitors, the dielectric constant is higher, the withstand voltage management and energy storage capacity are larger, and the capacitor has the advantage of releasing energy quickly. The disassembled capacitor has no moving parts during operation, so the maintenance workload is extremely small and has high reliability.
At present, supercapacitors are gradually being used in power supply applications such as border guard posts and alpine meteorological stations. However, supercapacitors also have certain defects, such as capacitor series voltage equalization, large terminal voltage fluctuation range, and low energy density.
The supercapacitor and battery hybrid energy storage system combines the two energy storage devices organically, integrates the advantages of the two energy storage methods, compensates for the shortcomings of the two energy storage technologies, and improves the performance of the energy storage system.
A large number of studies have shown that the application of supercapacitor and battery hybrid energy storage system in the microgrid can improve the output capacity of the microgrid energy storage system, increase the discharge time of the energy storage system, and reduce the internal loss of the system; It reduces the number of battery discharge cycles, reduces the loss of the battery, and increases its service life. In short, the application of the supercapacitor and battery hybrid energy storage system improves the power quality of the microgrid and improves the stability and economy of the microgrid.
3 Microgrid energy storage technology development trend
China's microgrid energy storage technology is still in the initial stage of development, with great development space and prospects. First of all, we should speed up the research and development of high-efficiency and low-cost energy storage batteries, focusing on improving the storage speed of electric energy. Secondly, the single energy storage technology has limitations to a certain extent, and its improvement is limited by economic costs and other factors. .
Two or several energy storage technologies can be organically combined to foster strengths and avoid weaknesses. Finally, the owner of the energy storage device in the microgrid must obtain real-time grid information, including electricity prices and grid faults, in order to make the microgrid energy storage device The role is fully utilized.
As micro-networks play an increasingly important role in power systems, micro-grid energy storage methods and energy storage equipment are moving toward market-oriented management. Ensure that the users of the microgrid energy storage device can timely grasp the grid information, including the faults in the grid operation and the price of electricity, so as to ensure that the microgrid energy storage device plays its due role.
Analytical theory and method for the application of energy storage systems in microgrids: On the basis of fully understanding the dynamic characteristics of microgrids containing energy storage devices, the complex nonlinear electromagnetic problems inside energy storage devices, and energy storage devices and systems are studied. The interaction between components.
4 Summary
Energy storage technology plays an important role in the stability of microgrid operation. According to the limitations of single energy storage technologies such as batteries and supercapacitors, this paper proposes a supercapacitor and battery hybrid energy storage system. The energy storage system not only combines the advantages of the two, but also effectively compensates for the defects of the two. , improve energy storage efficiency. The application of the hybrid energy storage system in the microgrid is of great significance for realizing the internal voltage balance of the microgrid and improving the economics and stability of the microgrid operation.
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