What is the difference between energy storage battery BMS and button cell battery cr1620?

1 Application scenarios of large-scale energy storage systems

In order to achieve the purpose of smoothing output power fluctuations, more and more power plants are equipped with energy storage systems, such as new energy power stations, wind power stations or solar power stations.

Independent energy storage power stations, as the reform of the power system gradually enters people's field of vision, independent energy storage power stations that make a living by reselling electricity are gradually emerging.

Microgrid, a small power supply and distribution network that includes distributed power sources, power loads, energy storage systems and power grid management systems. In order to ensure the continuity and stability of power consumption of loads, each microgrid will be equipped with an energy storage system.

Indoor energy storage power station

2 Differences between energy storage battery management system (ESBMS) and power lithium battery management system (BMS)

The energy storage battery management system is very similar to the power lithium battery management system. However, the power lithium battery system is in a high-speed moving electric vehicle, and has higher requirements for the power response speed and power characteristics of the battery, the SOC estimation accuracy, and the number of state parameter calculations.

The scale of energy storage system is very large, and the centralized battery management system is obviously different from the energy storage battery management system. Here we only compare it with the distributed battery management system of power lithium battery.

2.1 The position of battery and its management system in each system is different.

In the energy storage system, the energy storage battery only interacts with the energy storage converter at high voltage. The converter takes power from the AC power grid to charge the battery pack; or the battery pack supplies power to the converter, and the electric energy is converted into AC by the converter and sent to the AC power grid.

For the communication of energy storage system, the battery management system has important information interaction relationship with the converter and the energy storage power station dispatching system. On the one hand, the battery management system sends important status information to the converter to determine the high-voltage power interaction; on the other hand, the battery management system sends the most comprehensive monitoring information to the dispatching system PCS of the energy storage power station. As shown in the figure below.

Basic topology of energy storage system

The BMS of electric vehicles has energy exchange relationship with both the motor and the charger at high voltage; in terms of communication, it has information interaction with the charger during the charging process, and has the most detailed information interaction with the vehicle controller during the entire application process. As shown in the figure below.

Electric vehicle electrical topology

2.2 Different hardware logical structures

Energy storage management system, hardware generally adopts a two-layer or three-layer mode, and the larger scale tends to use a three-layer management system, as shown in the figure below.

Block diagram of three-layer energy storage battery management system

Power lithium battery management system, only one layer of centralized or two distributed, basically no three-layer situation. Small cars mainly use one layer of centralized battery management system. Two-layer distributed power lithium battery management system, as shown in the figure below.

Block diagram of distributed electric vehicle battery management system

From the functional point of view, the first and second layer modules of the energy storage battery management system are basically equivalent to the first layer acquisition module and the second layer main control module of the power lithium battery. The third layer of the energy storage battery management system is a new layer added on this basis to cope with the huge scale of energy storage batteries.

Let's make an analogy that is not so appropriate. The best number of subordinates for a manager is 7 people. If the department continues to expand and 49 people appear, then 7 people have to choose a team leader, and then appoint a manager to manage these 7 team leaders. Beyond personal ability, management is prone to confusion.

Mapped to the energy storage battery management system, this management capability is the computing power of the chip and the complexity of the software program.

2.3 Communication protocols are different

The energy storage battery management system basically uses the CAN protocol for internal communication, but its external communication, which mainly refers to the energy storage power station dispatching system PCS, often uses the Internet protocol format TCP/IP protocol.

Power lithium batteries and the electric vehicle environment in which they are located all use the CAN protocol, but they are distinguished by using internal CAN between the internal components of the battery pack and using the whole vehicle CAN between the battery pack and the whole vehicle.

2.4 The parameters of the management system vary greatly depending on the type of battery cells used in the energy storage power station.

For safety and economic considerations, when selecting lithium-ion batteries, energy storage power stations often use lithium iron phosphate, and some energy storage power stations use lead-acid batteries and lead-carbon batteries. The current mainstream battery types for electric vehicles are lithium iron phosphate ion batteries and ternary lithium ion batteries.

Different battery types have huge differences in external characteristics, and battery models are completely incompatible. The battery management system and battery cell parameters must be one-to-one corresponding. The same type of battery cells produced by different manufacturers will have different detailed parameter settings.

2.5 Different threshold setting tendencies

Energy storage power stations have more space and can accommodate more batteries, but some power stations are located in remote areas and transportation is inconvenient, so large-scale replacement of batteries is difficult. Energy storage power stations expect batteries to have a long life and not fail. Based on this, the upper limit of its working current will be set relatively low to prevent the battery cells from working at full load. The energy and power characteristics of the battery cells should not be particularly high. The most important thing is to look at the cost performance.

Power lithium batteries are different. In the limited space of the vehicle, the battery that is finally installed hopes to maximize its capabilities. Therefore, the system parameters will refer to the battery's limit parameters, and such application conditions are harsh for the battery.

2.6 The number of state parameters required to be calculated by both is different

SOC is a state parameter that both need to calculate. But until today, there is no unified requirement for energy storage systems, and what state parameter calculation capabilities the energy storage battery management system must have. In addition, the application environment of energy storage batteries has relatively ample space and a stable environment, and small deviations are not easily perceived in large systems. Therefore, the computing power requirements of the energy storage battery management system are relatively lower than those of the power lithium battery management system, and the corresponding single-string battery management cost is not as high as that of the power lithium battery.

2.7 The application conditions of the energy storage battery management system are relatively good

The energy storage power station has an urgent requirement for the balancing ability of the management system. The scale of the energy storage battery module is relatively large, and multiple strings of batteries are connected in series. The larger single-cell voltage difference will cause the capacity of the entire box to decrease. The more batteries are connected in series, the more capacity is lost. From the perspective of economic efficiency, the energy storage power station must be fully balanced.

In addition, due to the ample space and good heat dissipation conditions, passive balancing can better play its role, and a relatively large balancing current is used, and there is no need to worry about excessive temperature rise. Low-cost passive balancing can be used in energy storage power stations. The cascade utilization of power lithium batteries, what can retired power lithium batteries be used for? The reason why power lithium batteries are retired when the remaining capacity is 80% is that, in addition to the shorter driving range and the poorer user experience, the consistency after aging is poor and the system reliability is reduced, which should be an important reason for stopping their use in high-speed vehicles. Starting from here, there is a general direction for considering the scenarios of cascade utilization of power lithium batteries. The energy density requirement is not that high, the reliability can be enhanced by other means or the reliability requirement is not high at all, and it is more sensitive to cost, hoping to obtain a low-cost energy storage device.

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