Understanding MW-class containerized battery energy storage system in one article

MW-class containerized battery energy storage system (CBESS) is an important support for future power grid development, which can effectively improve power systems' stability, reliability, and power quality.

In recent years, the global MW-class battery energy storage technology has developed rapidly, and the containerized battery energy storage system has the advantages of high capacity, high reliability, high flexibility and environmental adaptability, which has a wide application prospect in the power grid system. The lithium battery energy storage system is more mature than other energy storage batteries, and the upstream and downstream industry chain is complete, so there is more room for cost reduction; at the same time, in countries where clean energy is not effectively utilized, the power system is in the situation of tight power supply during peak periods, low utilization of transmission and distribution capacity, shortage of active and reactive reserves and low transmission efficiency. The user side is also putting higher demands on load-side power quality. All these problems have accelerated the rapid development of energy storage technology.

Energy storage technology has become one of the key technologies for the development and construction of smart grids, which has the ability to improve the low energy quality of the grid and increase the utilization of renewable energy. With the rapid development of a new generation of lithium battery materials and further improvement of battery technology, there is a wide range of space for the application of lithium batteries in energy storage. Container battery energy storage system has the advantages of mature technology, large capacity, mobile, high reliability, no pollution, low noise, adaptability, expandable, easy to install, so the container energy storage system as a power system energy storage power is the future development direction of energy storage.

1. Overview

The MW-class containerized battery storage system is a lithium iron phosphate battery as the energy carrier, through the PCS for charging and discharging, to achieve a variety of energy exchange with the power system, and can be connected to a variety of power supply modes, such as photovoltaic arrays, wind energy, diesel generators and power grid and other energy storage systems. The output of the energy storage system can be connected to the grid, supplying various load equipment and electric vehicle chargers, etc.

Distributed power sources such as diesel generators, photovoltaic power generation, wind power generation, and battery storage systems are connected to the low-voltage AC bus in a relatively decentralized manner and then connected to the 10 kV or higher voltage grid through a step-up transformer, as shown in Figure 1.

When the main power source of the microgrid is an energy storage system or a diesel generator, the microgrid has two modes of operation as system voltage or FM reference.

Figure 1   Microgrid grid topology

(1) Wind storage operation mode: The energy storage battery system maintains the stability of the microgrid system voltage and frequency through a constant frequency and voltage (V/F) control strategy. In this mode of operation, the diesel generator is at a standstill and the wind power generation system generally adopts the maximum output power tracking control strategy. When the wind power output power is greater than the load consumption power and the state of charge (SOC) of the storage battery system is high, it also needs to run in the power-limited state.

(2) Wind diesel storage operation mode: diesel generator (through excitation and speed control) or wind generator, the establishment of microgrid system voltage and frequency reference, energy storage battery system using constant power control (PQ) strategy, through the receipt of background control system commands, receive the charging / discharging orders to the energy storage battery system.

2. Design

MW-level containerized battery energy storage system includes lithium battery pack, battery management system, energy conversion system, control system and other equipment. The core technologies are battery pack, battery cluster structure design, battery system thermal design, battery system protection technology, battery management system, etc.

MW-level container energy storage system consists of the battery system and energy conversion system, the battery system contains advanced lithium iron phosphate modules, battery management system and DC short circuit protection and circuit isolation fuse switch, all the equipment is centrally installed in the container. To meet the capacity output requirements, several battery modules are connected into a battery cluster, the DC output of each battery cluster in the battery system, connected to the energy conversion system, will be DC-AC and AC-DC (bi-directional), and control the power. Figure 2 shows the main component topology of an MW-scale container energy storage system.

Figure 2   Internal composition of the energy storage system

Compared with the traditional energy storage power plant, it has the features of simple installation and commissioning, beautiful appearance, etc. It is especially suitable for the application of grid-connected or off-grid energy storage systems in complex environments such as high altitudes, colds, islands and deserts.

3. Structure

The MW-class containerized battery energy storage system is a 40-foot standard container with two built-in 250 kW energy storage energy conversion systems, which integrates 1 MWh lithium battery system, battery management system, energy storage monitoring system, air conditioning system, fire protection system, and power distribution system in a special box to realize a highly integrated, large-capacity and movable energy storage equipment with heat insulation, constant temperature, fire retardant, windproof, and other features. Constant temperature, fire retardant, soundproof, etc., to meet the use of various environments.

The MW-class containerized battery energy storage system contains a battery system, battery management system, energy conversion system and control system. As shown in Figure 3: the black part is the battery room with six battery clusters in parallel, the gray part is the energy conversion system, air conditioning system and control system, and the purple part is the air duct.

Figure 3    Structure of the container battery system 

Figure 4    Internal diagram of the container battery system

4. Advantages

The MW-level containerized battery energy storage system designed in this paper has the features of being mobile, flexible, expandable, and detachable, which has certain practical value both from the commercial point of view and from the technical point view, in addition, it has advantages in the military field and environmental adaptability. Its main features are the following.

(1) Modular design: ISO is the standard size, allowing easy ocean transport and road transport. They can be suspended from overhead cranes, ships, trucks and temporary sites.

(2) Rugged design: ISOs protect cargo during transportation and will provide excellent protection from the weather, transportation and other environmental aggressions for the life of the energy storage system.

(3) Design for Mobility: In a comprehensive comparison of other energy storage batteries, Li-ion battery energy storage technology has the advantage of mass and volume, mobility, and is not limited by geography.

(4) Flexible base design: The container is easily applicable to any desired option. This includes access to equipment such as air conditioning, photovoltaics, fans, access doors, power cable access and others.

5. Applications

With a 1 MWh energy storage system as a unit, it has wide applicability and can expand capacity by combining multiple units in parallel, which has a good competitive advantage and can also be connected to new energy sources or connected to the grid as a distributed power source of smart grid.

(1) New Energy Access

As wind and solar energy are characterized by high randomness, intermittency and fast power changes, new energy directly connected to the grid, especially large capacity access to the grid, will have a certain impact on the scheduling and control of the grid, and even interfere with the stability of the grid. Through the joint application of battery energy storage system and renewable new energy, the randomly changing output power is converted into relatively stable output, which ensures the stability of the grid system.

(2) Backup power

In remote areas, areas with poor power supply reliability or important loads, MW-class battery storage systems can be used as backup power sources to provide power for grid systems that fail or for distribution systems that need to be overhauled. MW-class containerized battery storage systems can be shipped to an area and provide localized power sources. It can be used for emergency relief when severe weather damages the utility grid system or can be used in areas not yet connected to the grid. MW-class containerized energy storage systems can be connected to the grid for charging or can be configured for new energy access for energy storage power recharge.

(3) Microgrid

When the microgrid is operated in isolation, the randomness of distributed energy and user load is very large, which makes it difficult to ensure the real-time balance of power generation and consumption, resulting in a wide range of frequency fluctuations and drastic voltage fluctuations. Large-capacity and high-efficiency battery storage technology can suppress the interference of the external grid, ensure the power quality of local users, and further realize the smooth operation of the microgrid.

(4) Power quality

MW-class container battery storage systems can be permanently connected to the grid, thus providing the utility of fast-response frequency regulation of the grid.

(a) Renewable Smoothing: This can be used for wind farms and large solar PV arrays connected to smooth the output of these renewable energy systems.

(b) Remote Military Operations: Can be used for remote military operations without access to the utility grid to provide power. MW-class containerized battery storage systems can provide power for lighting, communications, and various military electronic hardware. Mobility can also improve the flexibility of use and expand new market business models, such as short-term rentability, temporary capacity increase, power for construction in progress, etc., with relatively large development space

(c) Others: Large-capacity battery storage technology can also be used to improve the power quality of distribution networks. The converter provides dynamic reactive power compensation, improves system voltage stability and copes with voltage dips; provides backup, peaking, power system stabilizer for the system, etc.

6. Conclusion

This time we have introduced in detail the concept, structure, core technology, and application direction of MW-level containerized battery energy storage system, whose application in the grid system is still in the stage of continuous development, and to achieve large-scale standardized application, a series of related problems such as cost, policy, environment and other non-technical and energy storage technologies need to be solved.

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