An effective energy storage method is of great significance to the safety and stability of microgrid operation and the balance of internal power supply. Since the output units of distributed units such as solar photovoltaic and wind power generation in the microgrid have the characteristics of randomness and intermittentness, and the power load also has the characteristics of random change, it has a great impact on the stability of the microgrid operation.
1. The role of the supercapacitor and battery hybrid energy storage system in the microgrid
There are two main operating modes of microgrid, namely grid-connected operation and islanded operation. In general, the microgrid operates in parallel with the conventional distribution grid. When a grid accident or power quality accident occurs, the microgrid adopts the island operation mode.
The conversion of these two operating modes will be involved in the operation of the microgrid, and a certain power shortage will be caused during the conversion process, which requires a certain battery energy storage device to ensure the balanced conversion of the two operating modes of the microgrid and enhance the stability of the microgrid.
In the process of some new energy power generation, due to the influence of external factors, there is often no power output. At this time, the energy storage system needs to provide power for power users.
Microgrids are small in scale, weak in self-regulation, load fluctuations and power grid failures will have a great impact on them. The hybrid energy storage system of supercapacitor and battery can effectively solve this problem. It can store excess electric energy when the load is low, and feed back the stored electric energy to the microgrid when the load peaks, providing help for the adjustment of the power of the microgrid.
Setting up a hybrid energy storage system of supercapacitors and batteries in the microgrid can solve the problems of voltage dips and voltage drops in the microgrid, and improve the power quality of the microgrid.
2. Hybrid energy storage system
Battery energy storage is currently one of the most widely used and promising energy storage methods in microgrids. The battery energy storage is used to solve the power demand during the peak load of the system, and the battery energy storage is also used to assist the reactive power compensation device, which is conducive to suppressing voltage fluctuations and flicker.
However, the charging voltage of the battery cannot be too high, and the charger is required to have voltage regulation and voltage limiting functions. The charging current of the battery cannot be too large, and the charger is required to have the functions of current stabilization and current limiting, so its charging circuit is also more complicated.
In addition, the charging time is long, and the number of charging and discharging is only hundreds of times, so the service life is limited and the maintenance cost is high. If it is overcharged or short-circuited, it is easy to explode, and it is not as safe as other energy storage methods.
Due to the use of harmful metals such as lead in the battery hybrid energy storage system, it also causes environmental pollution. Common batteries include lead-acid batteries, lithium-ion batteries for UPS systems, etc. With the advancement of science and technology, breakthroughs have been made in the research of flow vanadium batteries and sodium-sulfur batteries.
These two kinds of batteries have excellent characteristics such as high energy efficiency, long service life, and no discharge phenomenon, and have been used in some microgrid research systems. However, due to price reasons, large-scale deployment in microgrids will take time.
Supercapacitors refer to porous media made of special materials. Compared with ordinary capacitors, they have higher dielectric constant, greater withstand voltage management, and larger battery energy storage capacity. At the same time, they have the advantage of fast energy release from capacitors.
The disassembled capacitor has no moving parts during operation, so the maintenance workload is very small and it has high reliability.