402030 polymer battery

What is the difference between power402030 polymer battery BMS and energy storage battery BMS? Do you know?

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 the load, each microgrid will be equipped with an energy storage system.

2. The difference 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 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 positions of batteries and their management systems in their respective systems are different

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

For the communication of the energy storage system, the battery management system has an important information interaction relationship with the inverter and the energy storage power station dispatching system. On the one hand, the battery management system sends important status information to the inverter 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 relationships 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, energy storage power stations often choose lithium iron phosphate when selecting lithium-ion batteries, 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 passive balancing conditions for the application of energy storage battery management system are relatively good

Energy storage power stations have urgent requirements 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, energy storage power stations must be fully balanced.

In addition, due to 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.

BYD Battery Management System Revealed

Functions and Uses of Battery Management System BMS

1. Accurately estimate the state of charge (SOC) of power lithium battery packs, that is, the remaining power of the battery, to ensure that the SOC is maintained within a reasonable range, to prevent damage to the battery due to overcharging or overdischarging, so as to predict at any time how much energy is left in the hybrid vehicle energy storage battery or the state of charge of the energy storage battery.

2. Dynamically monitor the working status of the power lithium battery pack

During the battery charging and discharging process, the terminal voltage and temperature, charging and discharging current and total voltage of each battery in the power lithium battery pack are collected in real time to prevent the battery from being overcharged or overdischarged. At the same time, it can give the battery status in time, select the battery with problems, maintain the reliability and efficiency of the entire battery group, and make the realization of the remaining power estimation model possible. In addition, it is necessary to establish a historical archive of the use of each battery to provide information for further optimization and development of new types of electricity, chargers, motors, etc., and to provide a basis for offline analysis of system failures.

3. Balance between single cells

That is, charge the single cells evenly so that each battery in the battery pack reaches a balanced and consistent state. Balance technology is a key technology of a battery energy management system that the world is currently committed to researching and developing.

Decrypting BYD's battery management system

First, let's talk about the batteries of Tang and Qin. The models should be the same, but Qin's battery pack has fewer cells, with a capacity of 13 degrees, while Tang's has more, 18 degrees. Each cell is a lithium iron phosphate ion battery made by BYD itself, with a rated voltage of 3.2V and a capacity of 26AH. Why not the recently popular ternary lithium ion battery? The reason is as follows:

Lithium iron phosphate ion batteries have better life and safety, and are more suitable for plug-in hybrid vehicles.

The battery cell platform looks like this, but this should be on the bus, because the power storage capacity is as high as 120AH, and ours is only 26AH, but they are roughly the same, both are rectangular.

Tang's battery pack is located in the middle of the chassis, and its size and weight are relatively large. The advantage of placing it on the chassis is that it lowers the center of gravity of the whole vehicle, while not affecting the trunk space. As for the disadvantage, it has high requirements for water discharge and anti-collision. In daily use, you should pay attention to this part not to soak in water or bump.

This is the battery pack of Qin, which is located behind the back seat and before the trunk. Advantages: good water discharge and anti-collision performance, disadvantages: high center of gravity, affecting the trunk space, just opposite to Tang~

The connection method is series connection (all cells are connected in series), and the batteries in series are as shown in the figure below. To put it in a more vivid way, it is similar to the flashlight we used before, with several batteries connected head to tail.

In this connection method, each cell uses the same current to discharge when discharging, and the same current to charge when charging. Without the help of the balancing system, it is impossible to charge and discharge a single cell. Moreover, when a cell is full, the charging of the entire battery pack must be stopped, otherwise the cell will be overcharged and damaged, and when a cell is empty, the entire battery pack must stop discharging, otherwise the cell will be over-discharged and damaged.

Do you remember the requirements for the flashlight? By the way, old and new batteries cannot be mixed, that is, batteries with power and batteries without power cannot be mixed. Back to Tang and Qin's battery pack, there is a schematic diagram above, with several cells selected. Under normal circumstances, their storage capacity should be exactly the same, full together, and empty together. If this cycle continues, then the various problems at the beginning of the article will not occur. In fact, after the battery pack has been used for a period of time, there will be differences in the storage capacity of each cell. There are many reasons for the difference, such as inconsistent battery capacity, inconsistent internal resistance, inconsistent operating temperature, etc., which will lead to differences in discharge capacity. When the storage capacity of each cell is inconsistent, the following situation will appear:

On the surface, only one cell has lost a little power. There are so many cells in total, so there should be no impact, right? Let's continue to look down and see what happens when this battery pack is discharged:

The entire battery pack has released 80% of its power, and at this time, the originally full battery is empty, and the battery pack must stop discharging. If the battery pack has a storage capacity of 10 degrees, then when it is fully charged, this unbalanced battery pack cannot be discharged after discharging 80%, that is, 8 degrees. On the surface, only 5% of the power is missing, but 20% of the capacity cannot be used. This is only the case when there are only 4 cells. If there are more than 200 cells, you can imagine how big the impact is.

So what should we do if there is an imbalance? This requires the use of the balancing module of the battery management system. The balancing module of Tang and Qin adopts a passive balancing method, that is, the battery cell with a higher voltage is discharged through a bypass resistor to reach the same voltage as other cells. That is:

Each battery cell has a resistor controlled by the battery management system alone. When it is needed, the circuit of this resistor is connected to discharge the battery cell. After a certain period of time, this unbalanced battery pack becomes like this:

The battery cell capacity is consistent, and it can be fully charged and discharged. Everything returns to normal, the capacity is back, and the battery life is back! It sounds beautiful, right? Then why can't many cars achieve this effect?

First of all, the discharge process is very slow! During the charging process, the current can reach more than 10A (10000ma), and what about the discharge? It is understood that the maximum current allowed by this discharge resistor is 30ma~ When the balancing system is always in the best balancing state, it takes about 100 hours to balance the difference of one kilowatt-hour of electricity!

Secondly, the balancing system does not always work in the best state. To have a good working state, the system must know which battery cell is to be discharged and how much electricity to discharge. And this process cannot be completed with any power.

This is a curve chart of the discharge of a lithium iron phosphate battery. It can be seen that when the power is above 15%, the voltage difference is very small. At this time, it is very difficult or even impossible to find which battery cell to discharge and how much to discharge. Therefore, to keep the balancing system in an efficient working state, it is necessary to use the battery to less than 15% in real time. Then fully charge and let the car enter the balanced state. At this time, the balancing efficiency is the highest. Unless you use the car, it is recommended to wait until the balancing is completed (that is, the dashboard is completely off). In the case of an unbalanced battery pack, a balancing takes about 20 hours. You can calculate how many cycles are required according to the lack of power in your battery pack.

This leads to another question: after the equalization is completed, the vehicle will enter the equalization state again after a little use of electricity and then be fully charged. Should this time be counted as effective equalization? According to the author's relevant experience, this equalization is almost ineffective. Because the battery packs of Tang and Qin are not balanced, most of them are one or two cells with too low voltage, and a large number of other cells need to be discharged. When the battery is low, the remaining cells can be correctly marked. When the battery is high, the system will only mark the cell with the highest voltage when fully charged. It is one, and you can imagine how efficient it is, which can be almost ignored.

Let's talk about what kind of battery is fine and what kind is problematic. Here, the DCT software battery monitoring module of 14 Qin is borrowed to display the data. Tang does not support this, but the principle of the battery pack is the same. When many people go to check the battery, they find that their lowest voltage cell is only 2.6-2.8V, and they feel that there is a problem with this cell, and then ask the 4S shop to replace it. 4S applies the manufacturer's form and gives a normal reply, and the customer will feel that the manufacturer is perfunctory. In fact, it is normal for a single cell to have a low voltage. The most ideal situation is that when the battery is 5% charged, all the voltage cells are lower than 3V, so that all the power of the battery pack is released. Of course, such a battery pack almost does not exist, and it requires the consistency of all the cells to be very, very good. Generally speaking, the basis for judging that the battery pack is in good condition is that at 5%, the lowest cell voltage is lower than 3V, and the highest cell voltage is lower than 3.15V (discharge to 5% instantaneous voltage, the voltage will rise after being stored for a while, do not wait for it to rise). Battery replacement manufacturers have their own standards. If the conditions for replacement are met, you can choose to replace it, but the original poster recommends using the correct balancing method to balance for 100 hours, and then replace it if the effect is not obvious. Because it is difficult to match the replaced cell with the original cell that has already decayed. The following is a complete record of the balancing situation of the original poster's car:

Before the car was balanced, the meter showed that 8.5 degrees were charged, and the pure electric mileage of the golden right foot was barely 55KM. There were three sets of batteries with problems. I went to the 4S shop,The test indicated that it could be replaced, but the OP did not change it, but insisted on balancing. It can be seen that as time continues to accumulate, the voltage of the highest voltage battery cell in the car has been steadily decreasing, and the 240-hour balancing time has dropped from 3.247V to 3.111V. The power storage increased from 8.5 degrees on the meter to 11.5 degrees on the meter, and the power of the battery pack has been effectively restored. (Well, why is it not 13 degrees, but 11.5? 11.5 degrees on the 14-model Qin is already a very good result. Almost no 14-model Qin owner's meter can exceed 12 degrees. Don't ask why. My car's battery pack is marked as 12 degrees. It has been used for two years and has some natural decay.) In the most recent test, the voltage of the highest voltage battery cell has been lower than 3.1V, and the balancing condition is very good.

According to the experience of the original poster and Xia Ge of eCar Club, the battery balancing logic of Tang and Qin is roughly as follows:

First, the system will mark the battery to be discharged and the time to be discharged when the battery power is low (about 15%) and high (when the battery is fully charged and the power is turned off). Of these two marking methods, the marking when the battery power is low is obviously more effective and much more efficient.

Then, at the right time---when the car is powered on and fully charged (when the dashboard turns to the backlight and displays the red plug, but the backlight is not turned off), the battery management system discharges the battery to be discharged. When the marked time is reached, the balancing system is disconnected and the balancing is completed. When the next condition is ripe, mark again, discharge and balance again, and so on. This balancing process is divided into intra-group balancing and inter-group balancing, that is, the internal balancing voltage of each battery pack is balanced, and different battery packs must also be balanced. The specific logic of this process is not yet understood, but for users, it is enough to understand the overall balancing logic.

This is the case where the original poster's car has been used for 5% recently. The original poster used this time to do a balancing experiment. The purpose is to test the logic of the balancing system discharge. At the middle charge level, the voltage difference between the cells is very small, so the marking at this time will affect the efficiency. If you want better balancing, you should use low charge!

At 5%, the voltage difference is 0.15V, while at 43%, it is only about 0.008V.

This is the situation of the battery pack when it is about to be fully charged (it can be seen that the OP's car is 96% full, because it is almost full now). The cut-off voltage of Tang and Qin charging should be around 3.7V. If a cell exceeds 3.7V, charging will be stopped immediately. The moment the OP took this photo, charging was stopped. It can be seen that the voltage of the lowest voltage cell of this battery pack is also over 3.52V, which shows that the balancing state of this car is very good.

This is the voltage after the full balance is completed and placed for a few hours.

This is the situation after a complete balance is completed, using 5%. It can be seen that the cells with the lowest voltage in each group basically did not appear in this table. The change in the number of the lowest voltage cell means that the balancing system has completed its task well: by discharging other cells and then charging them together, the voltage of the lowest voltage cell is raised.

Battery power: Currently it is 21.8AH, not quite 11 kWh. It was 24, 12 kWh when it left the factory, but it was full at 92%. In 2 years, it has basically not decayed, which is still good. Of course, it is a bit entangled that it is not enough to 13 degrees, but fortunately, 70KM is stress-free when the endurance temperature is suitable.

The problem of scheduled charging and balancing, which has been discussed more before, has basically figured out the logic through Xia Ge's exploration.

The conclusion is roughly: scheduled charging does not have the function of trickle charging, and the battery pack cannot be charged. The balancing system is started at this time, but the operating efficiency is very low, and it can only discharge 1-2 cells, and the effect is almost negligible. Scheduled charging is still used when using the valley electricity price. It is unscientific to try to use appointment to increase the balancing time.

Earlier, we introduced the working mode of the battery pack, the working logic of the balancing system, and how to judge the status of the battery pack. Let's talk about the reasonable balancing method summarized by friends:

1. Use the car normally until the battery pack has a low power level (recommended below 20%, above 10%)

2. Plug in and charge. Do not turn off the power until the charging is completed. Let the balancing system fully balance until the dashboard is completely black (if you use the car, you can drive away, and the previous balancing hours are still valid)

3. Use the car normally after completion.

This is a cycle. The balancing time is effective balancing, and the rest is to accumulate enough time. Like the car of the original poster, the cumulative balancing time exceeds 200 hours to achieve a relatively perfect effect.

The balancing we talked about above is based on the premise that there is no problem with the battery cell. If a battery cell has a problem and the actual capacity is reduced, then no matter how hard the balancing system tries, it will be useless. So how to judge the battery cell problem?

The voltage inconsistency caused by the balancing problem is that the lowest voltage battery cell at 5% and the lowest voltage battery cell at 100% are the same. The problem with the battery cell causes the lowest voltage cell at 5% to have a higher or even the highest voltage at 100%. If your battery pack is like this, there is no other way but to replace the problematic cell!

Finally, let's answer the questions at the beginning of the article.

Insufficient charging capacity and insufficient pure electric range: There is a problem with the battery pack balance or a certain cell. The solution is to first determine which situation it is. The corresponding treatment opinions have been introduced in the previous article.

Charging jump: That is, when the battery pack is charging, it reaches 100% directly without passing through the subsequent percentages at a certain percentage (such as 96%). The reason is that the system's mark on the battery pack capacity is greater than the actual battery pack capacity. When charging to this percentage, the voltage of some cells has reached the voltage to terminate charging. Therefore, the system stops charging and determines that the power is 100% at this time. The cause of this problem is also insufficient charging capacity.

When the power is low, the power drops rapidly: Due to the discharge characteristics of lithium iron phosphate batteries, the voltage change is very low on a long platform in the middle, and the system can only estimate the remaining power. When the remaining power of the battery reaches 15% (the corresponding battery voltage is about 3.18V), the voltage will drop suddenly. Tang and Qin's battery management system will re-estimate the remaining power of the battery pack when a battery reaches this voltage. If the remaining power is displayed as 30% at this time, and the system re-estimates that it is only 15%, then the management system will increase the speed of power decline displayed on the instrument, resulting in 800 meters of running with 1% before, but only 400 meters at this time.

Dilemma of domestic battery management system BMS

The development of new energy vehicles is not smooth sailing. In the past two years, with the large-scale promotion and use of new energy vehicles, we have also heard a lot of scandals about new energy vehicles: spontaneous combustion, false mileage, etc. Why do these problems occur? The main reason is that the battery management system is not used or an inferior and immature battery management system is used. In fact, the safety of new energy vehicles has always been one of the key tasks of the government and the automotive industry.

Not long ago, the Ministry of Science and Technology, the Ministry of Finance, the Ministry of Industry and Information Technology, the National Development and Reform Commission and other four ministries and commissions have jointly issued a new energy vehicle demonstration and promotion safety order (i.e., the "Letter on Strengthening the Safety Management of Energy-Saving and New Energy Vehicle Demonstration and Promotion"), emphasizing that all plug-in hybrid vehicles and pure electric vehicles put into demonstration operation must be equipped with a vehicle operation technical status real-time monitoring system (BMS for short), especially to strengthen the monitoring of power lithium batteries and fuel power batteries. There are many reasons for the spontaneous combustion of electric vehicles, and it is not that you can sit back and relax after installing a battery management system. For example: in terms of safety, accuracy, life, and discharge capacity, a single battery can be charged and discharged 2000 times, but it may only be 1000 times after forming a battery pack. If an immature BMS is installed, it is impossible to monitor the battery charging and discharging status in real time and accurately, which can easily cause excessive power consumption of the local battery cell and local heat, and the information cannot be transmitted to the driver, which can easily lead to battery spontaneous combustion. Industry insiders believe that installing an excellent battery management BMS can effectively improve the utilization rate of the battery, prevent the battery from overcharging and over-discharging, and extend the battery life. It monitors the operating status of the battery pack and each battery cell, effectively prevents the battery pack from spontaneous combustion, and warns the driver in advance of emergencies in case of emergency, thus winning time for safety.

The future of new energy vehicles and battery management systems

my country's new energy vehicle industry began in the early 21st century, and has only been developed for more than a decade. Due to people's desire for environmental protection and renewable energy, new energy vehicles have ushered in development opportunities, and then they have become unstoppable. In the long future, new energy vehicles will act as a challenger to invade the vast market that originally belonged to traditional fuel vehicles, and due to the development of society, this kind of market share occupation is foreseeable.

While looking forward to the rapid development of new energy vehicles, we must clearly realize that the development of technology is the foundation of the industry's development, and stable, efficient, safe and reliable products are the embodiment of technology. We must understand that the current domestic new energy vehicle industry is not friendly. The frequent electric vehicle spontaneous combustion incidents and false mileage have exposed the current domestic new energy battery packs and battery management system design, testing, and production standards are imperfect.

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