What are the applications of high efficiency battery equalizer technology in cascade storage batteries

Battery equalization technology can improve the service life and prolong the service time of the battery pack, which is suitable for high-capacity NiMH, 2V lead-acid battery, lithium battery, 6V lead-acid, 12V lead-acid battery pack, and supercapacitor pack.

Step battery and selection

Cascade battery refers to the battery which has been used and has reached the original design life and whose capacity can be fully or partially recovered by other means.

Generally, after 5 years of use, the effective capacity of the battery is about 80%. Battery of natural attenuation into the stable period, can according to the small capacity battery, through a certain number of parallel use of battery, the available capacity for several times, fully meet the needs of the energy storage and power, to this point and to increase the range of electric vehicle, using a large number of cells in parallel to increase battery capacity of truth is the same.

Battery in the use of five years later, the available capacity and battery life significantly shortened, users and dealers often whole change, little imagine, is not a battery pack all batteries need to be replaced, are just one or a few of the battery capacity of the serious attenuation affects the whole battery pack, if there are multiple such batteries, by checking out serious attenuation of the battery, battery capacity and internal resistance tests, other can pilot use again. The cascade utilization of power battery obviously prolongs the use efficiency and life cycle of the battery and reduces the environmental pollution brought by the battery.

The reuse of power battery is a key link of the power battery industry chain to form a closed loop, which has important value in environmental protection, resource recovery and improving the whole life cycle value of power battery. After being tested, screened and reassembled, the retired power batteries are still capable of being used in low-speed electric vehicles, backup power sources, power storage and other fields with relatively good operating conditions and low requirements for battery performance.

With the increasing promotion and application of new energy vehicles, a large number of retired batteries will be produced every year.

Cascade battery utilization can improve the utilization rate of the battery and extend the life cycle of the battery, which is of great significance in terms of energy saving and environmental protection. However, some matters should be noted in cascade battery utilization:

1. Use basic cell as far as possible, such as 2V single lead-acid battery and various lithium batteries, including lithium iron phosphate battery, lithium titanate battery, lithium ternary battery, lithium cobalt acid battery, and lithium manganese acid battery. Batteries that are packaged in series with multiple units, such as 6V lead-acid battery (3 2V cells) and 12V lead-acid battery (6 2V cells), are not suitable for cascade utilization. The main reason is that these batteries have multiple batteries inside, and they are unbalanced and cannot be solved externally.

2, must follow the same type of battery group principle. The battery group must be of the same type, that is, the working voltage range of the battery must be the same. Batteries with different operating voltages cannot be used in the same battery pack, nor can they be mixed even if they have the same capacity.

3. If possible, capacity, voltage and internal resistance measurement should be carried out before assembly of battery groups. Batteries with similar capacity and internal resistance should be selected as far as possible to reduce the expansion of consistency difference during reuse.

As the capacity of cascade batteries is generally lower than the nominal capacity, in order to obtain sufficient capacity, more batteries need to be used to achieve the design capacity through proper series and parallel connection, so it is necessary to assemble according to the technical conditions.

Assembly method 1: first and then the string, such as electric vehicle battery pack using this way.

Assembly mode 2: first string and then merge, often used in a data center or computer room.

Both types of assembly methods have advantages and disadvantages and are suitable for different environments:

Disadvantages of first parallel and then serial: it is very important to choose the connection line and bus of the unit battery, otherwise it will cause the difference between charging and discharging of the battery. The leakage current (or fault) of individual batteries will affect a parallel unit, which has a large impact on the capacity and directly affects the battery life (mileage). Advantages: easy to manage, if you add a battery equalizer only need a set (set).

Advantages: easy connection, convenient maintenance, can quickly detect and deal with faulty batteries, easy maintenance, each in a string of cell battery capacity can be different, high battery utilization, capacity (power) can be arbitrary expansion, increase backup time, improve reliability, especially suitable for data centers; Cons: multiple sets are required if battery equalizer is added.

4, the following batteries cannot be reused: one is the leakage current (or high self-discharge rate) of the battery; Second, the appearance of deformation, such as shell expansion of the battery; The third is the leakage of battery.

Step battery equalization

Pilot battery even very strict screening, also hard to ensure the consistency of the battery, even excellent consistency of battery together, after dozens of charging and discharging cycle still can produce different degree of difference, and this difference can longer duration of use increase gradually, consistency will be more and worse, clearly show the battery voltage difference between grow less effective charge and discharge time. A large amount of testing data shows that the battery pack with poor consistency has the following characteristics:

1. The voltage of the cell presents obvious uneven and irregular distribution;

2. The residual capacity of the cell presents an irregular discrete distribution;

3. The internal resistance of the cell also presents an irregular discrete distribution.

Further statistical analysis of the test data shows that the biggest killer of battery imbalance is:

1. Due to the temperature difference of the battery, the installation of the battery pack is usually intensive. The battery temperature of each part is different, which affects the consistency of the battery and accelerates the difference between the batteries;

2, violent charging and discharging, accelerate the expansion of differences between batteries;

Energy storage battery capacity is very big, to a nominal 500 ah battery, for example, assume that the minimum and maximum capacity of your battery capacity difference is 50 ah, other differences ranging from 5 to 10 ah battery, the system of the maximum effective discharge capacity is 450 ah (tentatively the Numbers for D batteries, similarly hereinafter), assuming that discharge current 50 a, the theory of maximum discharge time is about 9 h. Beyond this time, D battery will reach the discharge cut-off voltage and enter the over-discharge state. If it continues to discharge, it will seriously damage D battery and its maximum effective capacity will be sharply reduced, thus further reducing the maximum effective capacity of the battery pack. It also involves a problem of discharge rate, the maximum capacity of battery discharge ratio is 0.1 C, D battery discharge ratio of 0.11 C, another battery discharge ratio is between 0.1 C and 0.11 C, the different discharge rate, the degree of attenuation of each battery is different, this will lead to the differences and battery consistency gradually expanded, and accelerating demands. Also, charging period, according to the charging ratio 0.1 C, D battery charging ratio is 0.11 C, is the biggest, the first to charge voltage limit, will continue to charge into the charging status, further damage to the D battery, other battery charging rate between 0.1 C and 0.11 C, charging ratio of the differences will add to the battery and consistency, and accelerating demands. Such a battery pack, after repeated charge and discharge, will eventually lead to smaller and smaller effective capacity, effective discharge time is shorter and shorter. Large capacity storage battery has a serious problem, that is the risk of thermal runaway problem, for this battery pack, if not for effective prevention and control, D cells may be a battery of battery charge and discharge process of highest temperature, easily happened thermal runaway breakdown, light battery completely scrapped, even cause the battery failure, or maybe even more serious joint problems, did not dare to imagine. If the battery pack can maintain each battery during operation without charging or discharging, then the effective capacity and discharge time of the battery pack can be guaranteed, and the battery pack is always in the state of natural attenuation. Thus, it can be seen that battery balance is very important for the normal and safe operation of the battery pack.

For the D battery in this example, if its discharge current can be automatically reduced to below 50A, such as 47 ~ 48A, and the insufficient 2 ~ 3A current is automatically provided by other batteries with large capacity, then the total discharge time can be more than 9h, together with other batteries to reach the discharge terminal, and no discharge will occur; Similarly, if its charging current can be automatically reduced to below 50A, such as 47 ~ 48A, the remaining 2 ~ 3A current will be automatically transferred to other batteries with large capacity, and the charging current of large capacity batteries will be automatically increased. If it reaches the charging limit voltage together with other batteries, no discharge will occur. It can be seen that the balance current must reach above 5A to meet the requirements, especially at the end of charging and discharging, from the balance principle, only transfer type battery equalizer can be competent.

At present, the progress of effective battery equalization technology is uneven, especially in the equalization current and equalization efficiency. Although some schemes have adopted synchronous rectification technology, the maximum equalization current is mostly limited within 5A, and the continuous equalization current is only 1-3a, which cannot meet the needs. Due to the need to support bidirectional balance, the efficiency of currency conversion is usually not high, and the heating problem of larger balance current is still prominent. Another important obstacle is the cost of equipment. Since most synchronous rectifier chips are used, the cost increases a lot.

Efficient battery equalization technology

At present, a kind of high-power, high-efficiency, real-time, dynamic transfer battery equalizer technology has been successfully developed by Zhou baolin of Daqing transportation bureau after many years. It with national patent technology (patent no. 201220153997.0 and 201520061849 X) as the core, and blended in a two-way synchronous rectifier technology invention (has applied for patents: a real-time battery which has the function of two-way synchronous rectifier shifting equalizer, application number: 201710799424.2), and this is a kind of don't need synchronous rectifier chip two-way synchronous rectifier technology, not only equipment cost greatly reduced, and the balanced significantly enhance current efficiency and equilibrium. It has achieved a breakthrough in balanced technical indicators, with the following characteristics:

1. Wide range of balancing current. Large equilibrium current means that the equilibrium speed is very fast, see the attached table. At present, the enhanced version of lithium battery equalizer has realized the relationship between equalization current and the voltage difference is about 1A/13mV. For example, when the voltage difference reaches 130mV, the equalization current can reach about 10A, which is especially beneficial to high-speed equalization.

2. High equilibrium efficiency. High equalization efficiency means less power loss, higher utilization rate and lower temperature rise of equipment, as shown in table 1.

3. Real-time dynamic balance. Battery static state, the maximum voltage in the group can be controlled within 10 mv or less (depending on the set of benchmark voltage difference), hand in hand to detail power consumption standby state detection, battery in charging status, or in discharge state, once the detected voltage difference is greater than the reference voltage difference, immediately into the equilibrium, real-time dynamic equilibrium is the biggest benefit effective equilibrium time is long, equalizer has the highest efficiency, its unique pulse technology has good maintenance and the battery capacity improvement effect, test has been applied.

The use of large current, high-efficiency battery equalizer can minimize the attenuation of the battery overcharge, overdischarge and thermal runaway failure. Even if the battery pack's capacity attenuation has formed the fact of poor consistency, it can also reduce its attenuation speed very well. By automatically forcing the voltage to maintain consistency, it can improve the effective capacity of the battery pack to a certain extent, extend the battery pack's cycle life, especially significantly reduce the maintenance and maintenance costs.

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