Peak shaving and frequency modulation power generation company overcomes the problem of large-capacity energy storage energy conversion

With the rapid development of power technology, the battery has grown from a few volts to thousands of volts, and the battery capacity can be as large as megawatts, but it can only output direct current. How to efficiently and quickly integrate DC power in a large battery energy storage system into the power grid has always been a worldwide problem. In large-capacity battery energy storage systems, energy conversion is a very important part. It is in the field of energy conversion that the key technology research team of the large-capacity battery energy storage system of the peak shaving and frequency modulation power generation company has proposed the internationally leading energy conversion technology for large-capacity energy storage systems with three-phase H-bridge cascade and transformerless grid access. The project achieved a major breakthrough.

Battery "wood barrel" effect

The picture shows the storage station No. 1 battery room

According to reports, the large-capacity energy storage power station is difficult to have a large number of batteries, and the consistency of the battery is highly demanded. Only after optimizing the voltage, capacity, and internal resistance, can it be used together. “It's just like a horse-drawn vehicle. Only energy can be maximized by walking in unison and using the same force,” said Chen Man, deputy director of the Maintenance and Test Center of the peaking and frequency modulation power generation company. The battery also has a “wooden barrel short board. "Effectively," traditionally, the battery packs are connected in series, which has the problem that the cycle life does not reach the design life. On the one hand, the decay rate of the individual cells is significantly faster than that of the other cells, thereby affecting the performance of the battery pack where the cell is located; On the one hand, the charge/discharge characteristics of each cell are inconsistent, and the difference in the charge/discharge characteristics of the cell causes an imbalance in the charge/discharge power, thereby damaging the overcharged or overdischarged cell and affecting the life of the entire cell.

It is reported that the lithium iron phosphate battery was used in the initial stage of the energy storage station project. Only the first-class battery equalization device was configured at the technical level at that time. The battery “short barrel effect” occurred significantly, and the lithium titanate used in the 863 demonstration project was used. There are large differences in the number of batteries and the number of charge and discharge times, and the number is larger. Therefore, how to maximize the benefits of different types of batteries in the new project by “seeking common ground while reserving differences” has become the primary problem solved by the project team.

In order to solve the problem of fast, comprehensive and dynamic energy balance, the Chen Man team first created a four-level equilibrium system between battery cells and modules, and within and between battery systems. “In the past, the batteries were all connected in series, and they were not only bulky, but also easy to 'lose everything'. The quality of one battery was enough to affect the operation of the entire battery energy storage system. Today, the battery system of the 863 demonstration project of the energy storage station is composed of 10,000. More than 5,000 single-cell batteries are used to effectively solve the 'wood barrel' effect through a four-level equilibrium system, which greatly improves the energy efficiency of the battery system.” Chen Man introduced.

High energy conversion efficiency, large capacity and fast response

The picture shows the 863 project 2 MW 10 kV cascaded energy storage system

Li Yongqi, head of Shenzhen Baoqing Battery Energy Storage Station, said that the 863 project of Shenzhen Baoqing Energy Storage Station has developed a three-phase H-bridge cascade, large-capacity energy storage system energy conversion technology without transformer access to the grid, and developed the world’s first 10kV high efficiency (98.3%), large capacity (2MW), fast dynamic response (not more than 5ms) energy storage energy conversion device. The overall efficiency of traditional low-voltage energy storage systems is less than 88%, and the loss of 10kV grid-connected transformers is not considered 2%. The efficiency of the project's transformerless access to high-voltage power grid energy storage systems can reach 90%, and the overall system efficiency can be increased by more than 2%. The combined efficiency of 10 kV grid points can be increased by more than 4%. Li Yongqi said that due to the adoption of a 10 kV H-bridge cascaded energy conversion technology, the energy conversion efficiency reached 98.3%. “Equivalent to 10 degrees of direct current can be converted to 9.83 degrees of alternating current.”

In addition to high energy conversion efficiency, the three-phase H-bridge cascade energy conversion technology can greatly increase the capacity of the energy storage system. The capacity of the 863 demonstration project energy storage energy conversion device is four times higher than that of the energy storage station project. The energy conversion technology can also realize that a single 10 MW capacity of the energy conversion system can be directly connected to a 10 kV power grid and a single 50 MW capacity can be directly connected to a 35 kV power grid. The research and development of multi-machine parallel coordination control technology based on the H-bridge structure can double the capacity of the energy conversion system, and is particularly suitable for applications with high-power energy storage applications of 100 MW or more.

“Blinks one eye is generally only 0.1 seconds, 1 millisecond is equal to 0.001 seconds.” Chen Man said that compared to the domestic average of 100 milliseconds and foreign companies 30 milliseconds of the overall energy storage system response time index, Shenzhen Baoqing energy storage plant overall The response time does not exceed 10 milliseconds, which greatly enhances the emergency response capability of the energy storage station in the power grid.

The results are fruitful

It is understood that the demonstration project of the 863 energy storage station was on-grid operation in 2014. To date, the primary and secondary equipment operations of the project have been generally stable and well-functioning, and there have been no system outages due to system research and design issues. Various performance indicators have reached and are partially better than expected.

Based on years of research, the team members have overcome difficulties for three years. The demonstration project of the 863 energy storage station has built a large-capacity battery energy storage system with the largest single-machine power, the highest output voltage, and no transformer high-voltage grid connection. Items (23 items have been authorized), 2 software copyrights, 7 utility model patents, 57 papers published (27 SCI/EI papers); 1 IEEE International Standard, 7 National Standards, 7 Line Items .

“The project research has solved the key technical problems of large-capacity battery storage power stations. The research results are major innovations in the field of large-scale battery energy storage, and they are of great significance in promoting the development of smart grids in China, the adoption of new energy sources, and the optimization of energy structure. In the energy conversion and battery balance control technology to reach the international advanced level.” Academician Cheng Shijie, Academician of the Chinese Academy of Engineering and other nine well-known experts in the industry conducted a technical appraisal of the research results and gave a high evaluation.

“The research and demonstration of key technologies for this large-capacity energy storage system have resulted in a series of major innovations in high-voltage, large-capacity long-cycle life, dynamic energy balance, and millisecond-level response. Many of the results are world-leading and can be considered as breakthroughs in this area. Sexual progress.” Academician Liu Yanlu of the American Academy of Engineering and Professor at the University of Tennessee commented on the project.

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