What is BMS for energy storage batteries and what are its functions？
2024-09-23
With the popularization of energy storage batteries and the large-scale construction of energy storage power stations, more and more people are aware of the importance of BMS for energy storage batteries and energy storage power stations. However, it is not known what role BMS plays in energy storage batteries.
Who determines the service life of power batteries?
What are the uses of BMS, why is it so important for the safe operation of energy storage, and what major changes will BMS face in the future? This article will answer the above questions, and I hope this article can help you understand BMS in depth.
The battery management system (BMS) is the core subsystem of the energy storage battery system that intelligently monitors battery charging and discharging, temperature protection, power balance, and information transmission. It is the "smart brain" in the battery.
People generally focus on the price trend or technology iteration of energy storage batteries and energy storage system integration. However, from the perspective of energy storage needs, the battery management system deserves more attention. Whether it is to pursue higher safety or higher efficiency, BMS is a key link.
1. What is a BMS?
BMS collects key parameters such as voltage, current, temperature, etc. of the battery pack in real time to accurately determine the health status, energy status and safety status of the battery, thereby ensuring the safe and reliable operation of the energy storage system. In particular, the accuracy and reliability of the data obtained by the BMS determine the quality and efficiency of the overall operation of the energy storage system.
2. Advantages of BMS
A complete battery energy storage system, commonly referred to as a BESS, can be strategically assembled from dozens, hundreds or even thousands of lithium-ion batteries, depending on the application. The rated voltage of these systems may be less than 20V or as high as 1500V, and the battery pack supply current range is up to 300A or more.
Any mismanagement of high-voltage battery packs can cause catastrophic disasters that endanger life. Therefore, BMS is essential to ensure safe operation. The benefits of BMS can be summarized as follows:
(1) Functional safety
This is particularly cautious and necessary for large-sized lithium-ion battery packs. But it is well known that even the smaller formats used in laptops can catch fire and cause great damage. The personal safety of users of products containing lithium-ion power systems leaves little room for battery management errors.
(2) Life and reliability
Battery pack protection management, both electrical and thermal, ensures that all cells are used within the declared SOA requirements. This delicate supervision ensures safe use of the battery and rapid charge and discharge cycles, and inevitably produces a stable system with the potential to provide many years of reliable service.
(3) Performance and range
BMS battery pack capacity management, where inter-cell balancing is used to equalize the SOC of adjacent cells on the battery pack assembly, allowing optimal battery capacity to be achieved. Without this BMS function to account for changes in self-discharge, charge/discharge cycles, temperature effects and general aging, the battery pack may eventually become useless. The basic parameters of lithium batteries such as SOC, SOH EOH are timely, please click here for reference
(4) Diagnostics, data collection and external communication
Supervision tasks include continuous monitoring of all battery cells, where data logging itself can be used for diagnostics, but is often used for calculation tasks to predict the SOC of all cells in the assembly. This information is used in balancing algorithms, but can be forwarded to external devices and displays to indicate available resident energy, estimate expected range or range/life based on current usage, and provide the health status of the battery pack.
(5) Reduced costs and warranty
Introducing a BMS in a BESS increases costs, and battery packs are expensive and potentially dangerous. The more complex the system, the higher the safety requirements, and therefore the more BMS supervision is needed. However, the protection and preventive maintenance provided by the BMS in terms of functional safety, life and reliability, performance and range, diagnostics, etc., guarantee that it will reduce overall costs, including those related to warranty.
3. What are the main uses of BMS?
(1) Current monitoring and protection
When charging, if the charging current is too large, the internal voltage of the battery will rise rapidly, the battery electrolyte will dissolve, release a lot of heat, and cause the temperature to rise. This will not only accelerate the aging of the battery, but also cause the battery to swell, leak, short-circuit, and even explode.
The purpose of current monitoring is mainly to prevent overcurrent. There are two maximum current limits for the battery, one is the maximum continuous current value, and the other is the instantaneous current peak. The generation of instantaneous peak current is related to the operating state of the energy storage battery. For example, when a large load power appliance is started, a peak current will be generated, and the peak current is obtained through real-time sampling of the sensor.
Continuous current is a long-term accumulated current. BMS can obtain it by integrating the current over a period of time.
The current size of the battery is like the blood flow of the human body. If the flow is too large, the heart rate will be too fast, and the human body cannot bear it, which will cause damage to health. If the current monitored by the BMS is close to the limit, it is necessary to control and reduce the available current; if it exceeds the limit, it is necessary to turn off the available current.
(2). Voltage monitoring and protection
When the vehicle is charging, the BMS samples the battery voltage in real time. When the monitored voltage value is close to the high voltage limit, the BMS will request to gradually reduce the charging current; when the high voltage limit is reached, the BMS will request to completely terminate the charging current.
During the discharge process of the energy storage battery, the battery voltage changes from high to low. If the battery remains in a low voltage state for a long time, it will cause the growth of tiny branch crystals on the electrode surface. These crystals will cause the self-discharge rate to increase, which will not only affect the performance of the battery, but also cause safety problems.
When the voltage is monitored to be close to the low voltage limit, the BMS will request the key load to reduce its current demand. For example, reduce the output power, output current, etc. The monitoring of current and voltage can ensure that the battery operates within the safe operating area (SOA) formed by the current and voltage limits.
(3). Temperature monitoring and protection
Battery performance and life will be reduced if the battery is continuously exposed to excessive heat. For example, when charging continuously at a temperature of 45°C, performance loss may be as high as 50%.
When the temperature is too low, the standard capacity and remaining energy of the battery will also drop significantly. Most lithium-ion batteries cannot be charged quickly below 5°C and should not be charged at all below 0°C. Because the electroplating phenomenon during low-temperature charging can cause serious damage to the battery.
Therefore, the BMS needs to monitor the temperature of the battery at all times. When the temperature is too low, it needs to be heated; when the temperature is too high, it needs to be cooled down. The heating and cooling are completed through the thermal management controller to make the battery work in the best temperature range as much as possible. (such as 30-35℃), which can protect the performance and extend the service life.
Too high a temperature can easily lead to thermal runaway, too low a temperature can cause the electrochemical process to be irreversible; too high a voltage can easily lead to overcharging, and too low a voltage can lead to over-discharge and short circuit in battery dendrites. There is also a safe operating zone between temperature and voltage.
(4). Capacity monitoring and management
The remaining capacity of the battery is expressed by SOC (State Of Charge), also known as the state of charge. The battery cannot be overcharged. After overcharging, the voltage will rise rapidly, and the extra energy will be converted into heat, causing damage to the battery.
Energy storage batteries are stacked by connecting multiple battery cells of the same specifications in series and parallel. In theory, the charging current can be cut off after each battery cell is fully charged. But in fact, the capacity decay rate, self-discharge resistance and external circuit of each battery cell are not exactly the same, resulting in different leakage or self-discharge rates.
In this unbalanced situation, the top battery will reach its charging limit in advance, that is, the charging current will be terminated before the other bottom batteries are charged to full capacity.
In this way, when discharging, the operating time of the battery pack will be limited by the battery cell with the lowest capacity. Unbalanced battery capacity will cause battery degradation, shortened working time, and there will be a risk of overcharging weak batteries.
So the capacity management must first balance the battery pack, with the goal of making the SOC of each adjacent battery cell in the entire battery pack roughly equal. For information about the hazards and solutions of imbalanced cells in battery packs, please click here to read.
4. Three major changes will occur in BMS in the future
(1). Connect BMS and EMS
As energy storage systems are included in various power market trading entities, their profit models have become diversified, requiring higher data processing and forecasting capabilities to optimize revenue.
The integration of BMS and EMS will enable energy storage systems to better handle complex data sources and huge data management needs. This integration not only enhances the system's data processing capabilities, but also helps predict electricity price trends and optimize battery charging and discharging strategies, thereby increasing the overall benefits of energy storage. The energy storage batteries produced by Infinite Power have achieved data communication and integration of BMS and EMS.
(2). From BMS to EMS
In the industrial and commercial market, energy storage systems need to have higher-level energy management and comprehensive control capabilities to meet complex energy needs and trading strategies.
The emergence of BMS+EMS integrated centralized control units represents the expansion of energy storage management systems from simply focusing on battery management to the management of the entire energy system. Such a step can achieve more comprehensive monitoring and more flexible trading strategies, providing more efficient energy solutions for industrial and commercial users. For example, HT ESS (link to the homepage of industrial and commercial storage) commercial energy storage battery users can automatically change the system operation strategy through the local management system.
(3). Launch of mobile applets
With the development of mobile Internet, users have an increasingly strong demand for real-time data monitoring and convenient management. Through mobile applets, users can easily achieve "one-stop handheld" energy storage power operation and maintenance management. This real-time data access and operation capability greatly improves operation and maintenance efficiency and reduces operation and maintenance costs. In addition, this also reflects the trend of digitalization and intelligence, allowing users to obtain power station information anytime and anywhere, so as to make timely and effective business decisions. For example, through the HT cloud platform, you can view the operation status of the energy storage system, power generation status, power consumption status, residual current, and data of each battery pack in real time.
Overall, these three changes point to one direction: energy storage BMS is transforming from a simple battery management system to a more comprehensive and intelligent data service and energy management platform.
This development trend not only improves the overall efficiency of the energy storage system, but also brings users a more convenient user experience, indicating that the future of the energy storage industry will focus more on data-driven and intelligent management.
Summary
Unlike the extremely crowded energy storage system integration track, BMS companies are relatively scarce. As the nerve endings of the energy storage system, BMS is responsible for improving the two major performances of energy storage safety and economy. In particular, the accuracy and reliability of the data obtained by BMS determines the quality and efficiency of the overall operation of the energy storage system. INFINITEPOWER HT continues to increase R&D investment, designing and developing a stable and high-precision BMS, and interoperating with the EMS system, providing great guarantees for the safe, intelligent and efficient operation of energy storage power stations.
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