Difference between power battery BMS and energy storage battery BMS

Difference between power battery BMS and energy storage battery BMS

1. Application scenarios of large-scale energy storage systems

For new energy power stations, wind power generation, or solar power stations, more and more power plants are beginning to deploy energy storage systems in order to stabilize output power fluctuations.

Independent energy storage power stations have gradually entered the field of vision with the reform of the power system, and independent energy storage power stations that rely on reselling electricity have gradually emerged.

Microgrid, the system contains a distributed power supply, electricity load, energy storage systems and a small power distribution network management system. In order to ensure the electrical continuity and stability of the load, each microgrid is equipped with an energy storage system.

2. Differences between ESBMS and BMS

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

The energy storage system has a large scale. There is a significant difference between the centralized battery management system and the energy storage battery management system. Here, we only take the power battery distributed battery management system as a comparison.

2.1 The battery and its management system are different in their respective systems

In the energy storage system, the energy storage battery only interacts with the energy storage converter at high pressure, the converter takes power from the AC grid, and charges the battery pack; or the battery pack supplies power to the converter, and the power passes through the converter. Convert to AC to send to AC.

The communication of the energy storage system and the battery management system mainly interact with the converter and the storage power station scheduling 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 storage system PCS. As shown below.

Energy storage system basic topology

The BMS of an electric vehicle has an energy exchange relationship with a motor and a charger on high voltage; in terms of communication, there is information exchange with the charger during charging, and the entire vehicle controller has the most detailed information on the application process. Information exchange. As shown below.

Electric Vehicle Electrical Topology

2.2 The hardware logic structure is different

In energy storage management systems, the hardware generally adopts a two-tier or three-tier model, and the larger-scale one tends to a three-tier management system, as shown in the following figure.

Three-layer energy storage battery management system block diagram

The power battery management system has only one layer of centralized or two distributed, and basically there will be no three-tier situation. Small cars mainly use a layered centralized battery management system. The two-tier distributed power battery management system is shown in the figure below.

Distributed Electric Vehicle Battery Management System Block Diagram

From a functional standpoint, the first and second tiers of the energy storage battery management system are basically equivalent to the first tier acquisition module and the second tier main control module of the power battery. The third layer of the energy storage battery management system is an additional layer based on this to deal with the huge scale of energy storage batteries.

It is not a proper analogy to fight. The best number of subordinates of a manager is seven people. If this department has been expanding and there are 49 people, then only seven people should select a group leader, and then a manager will be appointed to manage the seven group leaders. Beyond individual capabilities, management is prone to confusion.

Mapping to energy storage battery management systems, this management capability is the chip's computing power and software program complexity.

2.3 There are differences in communication protocols

The energy storage battery management system and the internal communication basically all use the CAN protocol, but it communicates with the outside. The external mainly refers to the energy storage power station dispatch system PCS, and often uses the Internet Protocol format TCP/IP protocol.

Power battery, where the electric vehicle environment is based on the CAN protocol, only using the internal CAN between the internal components of the battery pack, the battery pack and the vehicle use the vehicle CAN to distinguish between.

2.4 Different types of batteries used in energy storage power stations have different management system parameters

In consideration of safety and economy, a power storage station often uses lithium iron phosphate when selecting lithium batteries, and more energy-storage power stations use lead-acid batteries and lead-carbon batteries. The current mainstream types of electric vehicles are lithium iron phosphate batteries and three-element lithium batteries.

Different types of batteries, the external characteristics of a huge difference, the battery model can not be universal. The battery management system and battery parameters must have a one-to-one correspondence. The same type of batteries produced by different manufacturers will not have the same detailed parameter settings.

2.5 Different Threshold Settings

Energy-storage power stations are more space-efficient and can accommodate more batteries. However, some power stations are located in remote areas, which are inconvenient for transportation and large-scale battery replacement. This is a difficult task. The expectation of the energy storage station for the batteries is that they have a long life and do not fail. Based on this, the upper limit of its operating current will be set to a relatively low level and the battery will not be fully loaded. The energy characteristics and power characteristic requirements of the cell do not need to be particularly high. Mainly to see the price.

The power battery is different, in the limited space of the vehicle, it is difficult to install the battery, and hopes to maximize its capabilities. Therefore, the system parameters will refer to the battery's limit parameters, and such application conditions are bad for the battery.

2.6 Both require different numbers of state parameters

The SOC is a state parameter that both need to be calculated. However, up until today, there is no unified requirement for energy storage systems, and what state parameter calculation capabilities must exist for energy storage battery management systems. In addition, the application environment of energy storage batteries is relatively abundant, the environment is stable, and small deviations are not easily perceived by people in large systems. Therefore, the energy storage battery management system requires a relatively lower computational power than the power battery management system, and the corresponding single string battery management cost is also lower than that of the power battery.

2.7 It is better to apply passive equalization conditions to the energy storage battery management system

Energy storage power stations are in urgent need of the management system's ability to balance. The size of the energy storage battery module is relatively large, and a plurality of battery strings are connected in series. A larger voltage difference between the individual cells will cause the capacity of the entire box to decrease. The more series batteries, the more the loss capacity. From the perspective of economic efficiency, energy storage power stations need a sufficient balance.

And because of the abundant space and good heat dissipation conditions, passive equalization can work better, and with relatively large equalization currents, there is no need to worry about overheating. Low-cost passive equalization can flex its muscles at energy storage power stations.

BYD battery management system secret

The function of battery management system BMS

1. Accurately estimate the state of charge of the power battery pack

Accurately estimate the state of charge (SOC) of the power battery pack, that is, the remaining battery power, ensure that the SOC is maintained within a reasonable range, and prevent damage to the battery due to over-charging or over-discharging, thereby predicting the hybrid vehicle storage at any time. How much energy is left in the battery or the state of charge of the energy storage battery.

2. Dynamic monitoring of the working status of the power battery pack

During the charging and discharging process of the battery, the terminal voltage and temperature, the charging and discharging current, and the total voltage of the battery pack of each battery in the power battery pack are collected in real time to prevent overcharging or overdischarging of the battery. At the same time, the status of the battery can be given in a timely manner, and the problematic battery is selected to maintain the reliability and high efficiency of the operation of the entire battery, making it possible to realize the remaining battery estimation model. In addition to this, we also need to establish a usage history file for each battery to provide information for the further optimization and development of new types of electricity, chargers, motors, etc., to provide the basis for offline analysis system failure.

3, the balance between the single battery

That is, the equalization charge of the single cells enables the batteries in the battery pack to reach a state of equilibrium. Balanced technology is the key technology for a battery energy management system that the world is currently researching and developing.

Decrypt BYD battery management system

First of all, let's talk about the battery of Tang and Qin. The model should be the same, except that Qin’s battery pack has a relatively small number of batteries, a capacity of 13 degrees, and Tang’s more, 18 degrees. The individual batteries are BYD's own lithium iron phosphate batteries, rated voltage 3.2V, capacity 26AH. Why isn’t the recently-triggered ternary lithium battery? The reason is as follows:

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

The battery cell platform is like this, but this should be on the bus, because the electricity reserves up to 120AH, we only have 26AH, but roughly the same, all rectangular.

Don's battery pack is located in the middle of the chassis, and its size and weight are relatively large. The advantage of putting in the chassis is to reduce the vehicle's center of gravity without affecting the trunk space. Disadvantages Well, the requirements for water discharge and bump prevention are relatively high. Everyday use should be careful not to soak in water, and do not bump.

This is Qin's battery pack, located in the back seat, before the trunk. Advantages: Good anti-collision performance in water discharge, disadvantages: high center of gravity, affecting the trunk space, and Tang Zhenghao is relative ~

The connection method is serial (all battery cells are connected in series). The battery in series is shown in the figure below. The image is a bit similar to the flashlight we used before. Several batteries are connected end to end.

In this connection method, each cell discharges using the same current when discharging, and the same current is charged when charging, and a single cell cannot be charged or discharged without using an equalization system. Moreover, when a battery is full, it is necessary to stop charging the entire battery pack, or the battery will be overcharged and damaged. When one battery is empty, the entire battery pack will stop discharging, otherwise the battery pack will Put damage.

Do you still remember what the flashlight requires? By the way, the old and new batteries cannot be mixed, which means that batteries with electricity and no electricity cannot be mixed. Back to Tang and Qin's battery pack, a schematic diagram was taken above and several cell batteries were selected. Under normal circumstances, their electricity reserves should be exactly the same, they should be filled together, and should be vented together. If this cycle continues, there will be no problems at the beginning of the article. In fact, after the battery pack has been used for a period of time, there will be a difference in the amount of charge stored in each battery. There are many reasons for the difference. For example, the capacity of the battery itself is inconsistent, or the internal resistance is inconsistent, and the operating temperature is inconsistent. There is a difference in capacity. When the charge of each cell is inconsistent, the following figure will appear:

On the surface, there is only one cell that has lost a bit of power. There are so many cells that should not have any impact. We continue to look down and see what happens when this battery pack is discharged:

The entire battery pack released 80% of its power, and at this time, the originally dissatisfied battery was empty, and the battery was about to stop discharging. If the battery pack's power reserve is 10 degrees, then under the full condition, the unbalanced battery pack will not be able to discharge 80% of the discharge, that is, 8 degrees. On the surface, only 5% of the power is lost, but it leads to 20 % of capacity cannot be used. This is still the case when only four batteries are compared. If it is more than 200, it can be imagined how big the impact is.

What happens if there is an imbalance? This requires the use of an equalization module for the battery management system. Tang and Qin’s equalization module uses a passive equalization method, that is, discharge the higher voltage cell through the bypass resistor to reach the same voltage as other cells. That's it:

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

The battery capacity is the same, recharge can be full, discharge is empty, everything is back to normal, capacity is back, and battery life is back! It sounds beautiful, right? Why are so many cars failing to achieve this effect?

First of all, this discharge process is very slow! When the charging process, the current can reach 10A or more (10000mA), and this discharge it? It is understood that the maximum current allowed by the discharge resistor is 30ma~. In the case that the equalizer system is always in the optimal equilibrium state, the difference in equalized electricity is also needed for about 100 hours!

Second, the equilibrium system is not always working at its best. To have a good working condition, the system needs to know which cells need to be discharged and how much power needs to be discharged. This process can not be done with any power.

This is a graph of the discharge of a lithium iron phosphate battery. It can be seen that the voltage difference is very small above 15%. It is very difficult or even impossible to find out which cells need to be discharged and how much to put at this time. Therefore, to make the balanced system work efficiently, it is necessary to use the battery at a rate of 15% or less in real time. Then it is fully charged and the car is in equilibrium. The equilibrium efficiency at this time is the highest. Unless you use a car, you are advised to wait until the equilibrium is over (that is, the dashboard is completely extinguished). In the case of unbalanced battery packs, it takes about 20 hours for a balance to be equalized. Everyone can calculate how many cycles are needed based on the lack of power in their battery packs.

This leads to another problem: After the balance is over, a little electricity is used, then it is full, and the vehicle will enter a state of equilibrium again. Should this time be included in the effective balance? According to the landlord's experience, this equilibrium is almost ineffective. Because Tang and Qin's battery packs are not balanced, the vast majority are that the voltage of one of the two batteries is too low and they need to discharge a large number of other batteries. When the battery is low, the remaining battery cells can be marked correctly. Under high battery power, the system will only mark one battery cell that has the highest voltage when it is fully charged. This is one, and it can be imagined that the efficiency is almost negligible.

Here's what kind of battery is no problem, what kind of problem is there. Here, 14 pieces of Qin’s DCT software battery monitoring module were borrowed to display the data. Don does not support this, but the principle of the battery pack is the same. Many people go to check the battery, found that their own minimum voltage battery only 2.6-2.8V, I feel this battery problem, and then require 4S shop replacement, 4S apply the manufacturer's form, give a normal reply, the customer will feel the manufacturers Perfunctory. In fact, the lower voltage of a single cell is normal. The ideal situation is that 5% power is that all voltage cells are below 3V, so that all battery power is released. Of course, such a battery is almost non-existent. It requires that all batteries have very consistent it is good. In general, the basis for judging the condition of the battery pack is that in the case of 5%, the minimum cell voltage is lower than 3V, and the highest voltage cell voltage is lower than 3.15V (discharge to 5% of the instantaneous voltage can be stored After a while, the voltage will rise and it will not rise again.) Replacement battery manufacturers have their own standards, if you meet the conditions for replacement, you can choose to replace, but the landlord also recommends that you use the correct balance method to balance 100 hours, if the effect is not obvious and then change. Because the replacement of the batteries and the original batteries have been attenuated is difficult to match the same. Here is a complete record of the landlord’s car balance:

Before the car was evenly balanced, the meter showed 8.5 degrees of charge. The pure electric mileage gold was barely 55KM. There were three battery problems, and they had been to the 4S shop. The test showed that they could be replaced, but the landlord did not change, but insisted on equilibrium. It can be seen that with the continuous accumulation of time, the voltage of the highest voltage cell of the vehicle has been steadily decreasing, and the 240-hour equilibrium time has decreased from 3.247V to 3.111V. The storage capacity increased from 8.5 to 11.5 degrees, and the battery pack's power was effectively restored. (Amount, you say why is not 13 degrees, is 11.5, 14 paragraphs of Qin 11.5 degrees have already been very good achievement, there are almost no 14 Qin car meter can exceed 12 degrees, do not ask why, my car mentions car battery mark At 12 degrees, it took two years and some naturally attenuate. In the most recent test, the voltage of the highest voltage cell was already below 3.1V, and the equilibrium was very good.

According to the experience of the landlord and the e-car Xia, Tang and Qin’s battery equalization logic is like this:

First, the system will mark the batteries that need to be discharged and the time that they need to be discharged when the power is low (for 15%) and high (full of power off), and these two marking methods are obviously more marked when the power is low. Effective and much more efficient.

Then, at the right time - when the vehicle is known to be powered on and when it is fully charged (the instrument panel is turned into a backlight with a red plug, but the backlight is not turned off), the battery cell needs to be discharged through the battery management system. Discharge. After reaching the marked time, the equalization system is disconnected and the equalization ends. After the next condition is ripe, mark it again and discharge it again to equalize. This equalization process is divided into intra-group equilibrium and inter-group equilibrium, that is, the internal equilibrium voltage of each battery group, and the balance among different battery groups. This process does not understand the specific logic at present, but for the user, as long as you know the overall balance logic.

This is the case where the landlord's car recently used 5%. The landlord used this time to do a balanced experiment. The purpose is to verify the logic of a balanced system discharge. In the middle charge, the voltage difference of each cell is very small, so the mark at this time will affect the efficiency, you want a better balance, or use low battery!

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

This is the case of the battery pack when the battery is about to be fully charged (it can be seen that the landlord's car is 96% full because it is now full). Tang and Qin charge the cut-off voltage should be around 3.7V, there is a battery more than 3.7V will immediately stop charging, the landlord this photo shoot the moment, stop charging. You can see this battery pack, the voltage of the lowest voltage cell also exceeds 3.52V, which shows that the balance of this car is very good.

This is the voltage after a few hours after the balance is full.

This is the case where 5% is used after a complete equilibrium has been completed. It can be seen that the batteries with the lowest voltage in each group basically did not appear in this table. The change of the lowest voltage cell number represents that the equalization system has completed their task well: by discharging the other cells and charging them together, the voltage of the lowest voltage cell is raised.

Battery power: At present, it is 21.8AH, not much to 11 kWh. The factory is 24,12 kWh, but 92% will be full. In 2 years, there is no basic attenuation, and it is still good. Of course, not enough 13 degrees is also a bit tangled, but fortunately the endurance temperature is 70KM without pressure.

However, before discussing more issues concerning the balance of reservation charges, the exploration of Xia Ge has basically understood the logic.

The conclusion is roughly as follows: There is no trickle charging function for scheduled charging and the battery pack cannot be charged. The balanced system is started at this time, but the operating efficiency is very low, and only 1-2 batteries can be discharged. The effect is almost negligible. It is unscientific to try to use reservations to increase the equilibrium time when booking charging or using the price of a valley.

We introduced the working methods of the next battery pack, the logic of the balanced system, and how to determine the status of the battery pack. Below, let's take a look at the reasonable and balanced approach that the small partners collectively conclude:

1, normal car, to the battery lower battery (recommended 20% or less, more than 10%)

2, insert the gun charge, do not power off the end of the charge, so that the balance of the system fully balanced to the instrument panel black (if you can drive away, the balance of the front hours is still valid)

3, after the completion of the normal car.

This is a cycle, the balance of time is an effective balance, the rest is accumulated enough time. Like the landlord's car, the cumulative equilibrium of more than 200 hours to achieve a more complete effect.

The balance we talked about above is based on the fact that the batteries have no problem. If there is a problem with a cell and the actual capacity is reduced, then no matter how well the balanced system works, it will not help. How to judge the battery problem?

The voltage inconsistency caused by the equalization problem is 5% when the lowest voltage cell is the same as the lowest voltage cell at 100%. The battery problem leads to 5% when the lowest voltage cell has a higher voltage or even the highest voltage at 100%. If your battery pack is such a situation, then there is no other way to replace the problematic electricity. Core it!

Finally, answer some questions at the beginning of the article.

Insufficient charging capacity and lack of pure electric cruising range: There is a problem with the balance of the battery pack or there is a problem with one of the batteries. The solution is to first determine what kind of situation it is. The corresponding processing suggestions have already been introduced in the article.

Charging jump: When the battery pack is charging, it is at a certain percentage (for example, 96%), and the percentage that does not pass behind directly reaches 100%. The reason is that the system has more battery pack capacity than the actual battery pack. When charging to this percentage, the voltage of the cell already reaches the voltage at which the charge is terminated. Therefore, the system stops charging, and at the same time, it determines that the amount of electricity is 100%. The reason for this problem is that the amount of charge is insufficient.

When the battery power is low, the battery power drops rapidly: Because of the discharge characteristics of the lithium iron phosphate battery, the very long platform voltage variation in the middle is very low, and the system can only estimate the remaining battery power. When the remaining power of the cell reaches 15% (corresponding to the cell voltage is about 3.18V at this time), the voltage will suddenly drop. Tang and Qin’s battery management system will re-estimate the remaining capacity of the battery pack when the battery reaches this voltage. If the remaining battery capacity is displayed as 30% at this time, and the system re-estimates it as only 15%, then the management system It will increase the rate of decline in electricity displayed by the meter. The result is that the original 1% can run 800 meters, but only 400 meters can be run at this time.

The Difficulties of Domestic Battery Management System BMS

The development of new energy vehicles is not easy. In the past two years, with the large number of new energy vehicles being used, we have also heard many “scandals” about new energy vehicles: spontaneous combustion, false cruising range, and why. What are these usage problems? The main reason for not using a battery management system or using a poor quality, immature battery management system. In fact, the safety issue of new energy vehicles has always been one of the key tasks of the government and the automotive industry.

Not long ago, the four ministries and commissions including the Ministry of Science and Technology, the Ministry of Finance, the Ministry of Industry and Information Technology, and the National Development and Reform Commission have jointly issued the “Safety Order” for the demonstration and promotion of new energy vehicles (ie, the “Letter on Strengthening the Safety Management of Energy Conservation and New Energy Vehicles Demonstration and Promotion”), emphasizing “The plug-in hybrid vehicles and pure electric vehicles that have been put into demonstration operations should all be equipped with real-time monitoring systems for vehicle operating technology (BMS), and in particular, there should be a variety of causes for the spontaneous combustion of power batteries and fuel cell electric vehicles. Without installing a battery management system, you can sit back and relax. For example, in terms of safety, accuracy, longevity, and discharge capacity, a single battery can be charged and discharged 2000 times, and it may be only 1,000 times after it is assembled into a battery pack. If you carry an immature BMS, The battery charge/discharge status cannot be accurately monitored in real time, which can easily cause local power consumption of the battery core to be too large, generate local heat, and the information cannot be transmitted to the driver, which can easily lead to spontaneous combustion of the battery.Industry believes that installing excellent battery management BMS can effectively improve the utilization of the battery and prevent the battery from overcharging and Discharge and extend battery life, battery health monitoring and various single-core battery, the battery pack effectively prevent spontaneous combustion, in case of emergency in advance to make emergency warning to the driver, to gain time for security purposes.

The future of new energy vehicles and battery management systems

The new energy automobile industry in China began in the early 21st century. It has not been developed for more than a decade. Due to people's desire for environmental protection and renewable energy, new energy vehicles have ushered in opportunities for development. After that, they are out of control and in a long period of time. In the future, new energy vehicles will be used as a challenger to invade the vast market that originally belonged to traditional fuel vehicles, and due to the needs of social development, the encroachment of this market share can be expected.

While looking at the rapid development of new energy vehicles, we must clearly understand that technological development is the basis for the development of the industry, and stable, efficient, safe, and reliable products are the embodiment of technology. We must know that the current domestic The new energy automobile industry is not friendly, frequent spontaneous combustion events and false cruising range of electric vehicles have exposed the current domestic design of the new energy battery pack, battery management system, testing, production standards are not perfect.

The absence of technical parameters and standards, and no authoritative authority to conduct authoritative testing on BMSs produced by manufacturers, is currently the predicament of the domestic BMS market, resulting in a variety of BMS products that are difficult to popularize in large scale. At the same time, many domestic auto manufacturers and battery PACK companies are not sufficiently aware of the importance of BMS. They think that as long as the individual cell cores can be linked, they can guarantee the vehicle operation, and their safety will be fortunate. They will be blindly involved in the procurement of BMS. In pursuit of low prices, in order to sign a contract, some bad BMS suppliers only have to reduce BMS functional indicators or simply castrate part of their functions, thus burying hidden security risks. This is also irresponsible and damaging to the entire industry. Only by establishing a unified industry standard as soon as possible, suppressing manufacturers that do not meet the requirements of the market, and establishing a sound inspection system, can the battery management system and new energy vehicles have a sustainable development future. This is also the demand of many manufacturers and consumers.