The Frequency Regulation of MLTO
Applied in the Energy Storage Technology
Abstract: The energy storage system in the grid can enhance the power grid control and solve the high efficiency and comprehensive utilization of large scale intermittent renewable energy access.MLTO battery energy storage system with fast charging and discharging response, continuous 4C of the high rate charge discharge capacity, long service life, is very suitable for smart grid fast response energy storage applications. In this paper, the THINPACK MLTO powder technology,container energy storage system design and 1000V ESS system applied in the North American market is introduced.
Key words : LTO technology; Energy storage; Quick respond; Frequency regulation:AFC
1.MLTO powder technology
LTO as an anode active material has excellent structural stability and fast charge-discharge capability in Li-ion battery applications. However, during the charging and discharging process, the gas generation problem caused by the side reactions of LTO batteries greatly affects its life and limits the large-scale application of LTO batteries.
Chemical side reactions that occur on the surface of LTO materials. During the charging and discharging process, the side reaction between the electrolyte and the LTO material generates a reducing lithium salt.During charging, the reducing lithium salt is oxidized and generates by -products such as H₂O, CO,CO₂, C₂H4 and C3H6 . These side reactions allow the continuous generation of gas inside the battery and ultimately accelerate the decay of the battery. In order to solve the above problems, the research team of thinpackmodified the traditional LTO powder, and coated a layer of material with low chemical reactivity but good lithium ion conductivity on the surface of the powder to isolate the electrolyte and LTO . Contact between materials , thus avoiding the occurrence of side chemical reactions during the charging and discharging process of the battery.
Fig.1 Scanning electron microscope image of MLTO powder
Using MLTO powder as the negative electrode active material and the ternary material of shackles, diamonds and erbium as the positive electrode active material has excellent cycle life and service life. At room temperature, 100% DOD cycling tests were carried out for two years under 6C charge and 6C discharge conditions , and the test results are shown in Figure 2 . It can be seen that after 25 000 deep charge-discharge cycles, the discharge capacity of the battery remains about 75 % of the initial capacity.
Fig. 2 Cycle life curve of MLTO battery
2.Containerized energy storage system design
The energy storage system uses a 23V/60AE standard battery module, as shown in Figure 3 . The cells are configured in 10 series and 6 parallels. The all-round protection bracket is designed to support and protect the cells, and the electrical connection between the cells is fully automatic laser welding to ensure the stability of the product. The reinforced heat dissipation fin design ensures the heat dissipation of the battery under high-rate cycling. The internal integrated LECU unit with automatic equalizationfunction is used for the measurement of the cell status in the module and external communication. Module mounting components, power connectors, communication connections, etc. are provided outside the module.
Fig.3 MLTO schematic diagram of battery
Figure 4 shows a schematic diagram of the MLTO module installation. The module installation adopts a drawer structure, and the use of the guide rail makes the installation and replacement of the module very convenient. All electricity
The gas connection is designed as a blind-mate junction structure, all electrical connections to the module are completed after the module is inserted into the battery rack. The overall layout is clear and tidy. The system consists of two sets of battery cells. Each group of cells is 1000V/60AE, and the two groups of battery cells are connected in parallel. The maximum continuous charging and discharging power of the system reaches 500kW.
Fig.4 Schematic diagram of MLTO module installation
The battery system, fire protection system, air conditioning system, monitoring system, control center, data server, etc. are integrated in the container to ensure the safety, stability and reliability of the battery system during operation. A schematic diagram of the interior of the container is shown in Figure 5 . The local server can upload the system operation data to the monitoring center for real-time monitoring through the Ethernet, and send the fault and alarm information that occurs during the operation to the monitoring center management personnel at the first time.
Fig. 5 Schematic diagram of the interior of the container
Size of the container is a 20 -foot standard container, as shown in Figure 6 . And through the container transport identification and certification. The container system can be transported as an integral unit. All connections can be made in the junction box outside the container. The junction box is equipped with a glass window for easy observation of the status of the internal switchgear. Both the AC input circuit design and the DC output circuit design have manual disconnect devices to facilitate system power-off maintenance. At the same time, an indicator panel is also designed on the outside of the container to indicate the key design status of the whole system. Ensure real-time monitoring of key equipment during system operation .
Fig. 6 Schematic diagram of the exterior of the energy storage container
3.Application of MLTO battery energy storage system in North American fast frequency regulation market
PJM is the largest interconnected power system in North America with a total installed capacity of 106 000MW . In order to maintain a continuous balance of generation and load and maintain the system frequency, as shown in Figure 7 , regulation and frequency response services must be provided. In addition, the PJM simultaneously executes the load response plan, such as when the LMP of the system is high or an emergency occurs, the user can respond to reduce the load and can be rewarded. The L0TO battery energy storage system can well meet the working conditions of the frequency modulation market due to its excellent cycle life and rate capability.
Fig. 7 FM application intent
Figure 8 shows the current response curve of the L/TO battery system under the PJMI condition . It can be seen from Figure 8 that the current response in frequency modulation applications is very frequent, and the power requirements of the energy storage system are very high, while the energy requirements are small. Therefore, the low-capacity and high-rate system design can meet the power requirements of the grid on the one hand, and on the other hand. On the one hand, the smaller battery capacity can effectively reduce the cost of the energy storage system.
Fig.8 Current response of MLTO energy storage system in
PJM frequency modulation
Statistics also found that the on-time output rate of the battery under this working condition is very high, reaching 1800Ah/ day. Converted into battery cycle is about 10 times / day. The requirement of battery cycle ( converted to 100 % DOD, considering the life factor of different DOD cycles ) for one year of use has reached more than 2500 times. The L0TO with its 25 000 cycle life is ideal for this high cycle life requirement.
4 Conclusion
Based on advanced MLTO powder technology and battery system design and management ,THINPACK has developed a fast- response battery energy storage system for the North American frequency modulation market. The data shows thatthe application of the frequency modulation market has strict requirements on the power characteristics and life characteristics of the energy storage system .THINPACK MLTO battery system just meets the strict requirements of the frequency regulation market for energy storage systems. In the FM market in the future, MLTO batteries will have broad space and excellent performance.