What is the application of high-efficiency battery equalizer technology in cascade energy storage batteries

　　battery equalization technology can increase the service life of the battery pack and extend the use time of the battery pack. It is suitable for large-capacity nickel-metal hydride, 2V lead-acid batteries, lithium batteries, 6V lead-acid, 12V lead-acid and other battery packs and super capacitor packs.

　　battery equalization technology can increase the service life of the battery pack and extend the use time of the battery pack. It is suitable for large-capacity nickel-metal hydride, 2V lead-acid batteries, lithium batteries, 6V lead-acid, 12V lead-acid and other battery packs and super capacitor packs.

　　Step battery and selection

　　"Ladder battery" refers to a battery that has been used and has reached its original design life, and its capacity is fully or partially restored by other methods to continue to be used.

　　Generally used 5 years later, its effective capacity is about 80%. The natural attenuation of the battery enters a stable period, and it can be used as a small-capacity battery. By using a certain number of batteries in parallel, the available capacity can be increased several times, which fully meets the needs of energy storage and power. This is in line with the electric vehicle in order to increase the cruising range. , The principle of using a large number of parallel batteries to increase battery capacity is the same.

　　After the battery pack has been used for 5 years, the available capacity and battery life are significantly reduced. Users and dealers usually replace them as a whole. As everyone knows, not all batteries in a battery pack need to be replaced, but one or several of the batteries are seriously attenuated in capacity The entire battery pack is affected. If there are multiple such battery packs, the severely attenuated battery can be eliminated through testing, and the other batteries can be reused in cascades through the capacitance and internal resistance testing. The echelon utilization of power batteries significantly prolongs the use efficiency and life cycle of the batteries, reduces the environmental pollution caused by the batteries, and is hailed as a key development target at present and in the future.

　　Power battery reuse is a key link in the formation of a closed loop in the power battery industry chain, and has important value in environmental protection, resource recovery and improving the value of the full life cycle of power batteries. The retired power battery has undergone testing, screening, reorganization and other links, and is still capable of being used in low-speed electric vehicles, backup power supplies, electric energy storage and other fields that have relatively good operating conditions and low battery performance requirements.

　　With the continuous increase in the promotion and application of new energy vehicles, a large number of retired batteries will be produced every year, and the concept of echelon utilization of power batteries has emerged and received widespread attention.

　　The use of cascade batteries can increase the utilization rate of the battery and extend the life cycle of the battery. It is of great significance in terms of energy saving and environmental protection, but some matters must be paid attention to in the use of cascade batteries:

　　1. Use basic cells as much as possible, such as 2V single lead-acid batteries, various lithium batteries, including lithium iron phosphate batteries, lithium titanate batteries, ternary lithium batteries, lithium cobalt oxide batteries, and lithium manganate batteries Wait. Batteries that are packaged in series with multiple units, such as 6V lead-acid batteries (3 2V units) and 12V lead-acid batteries (6 2V units), are not suitable for cascading use, mainly because these batteries have multiple strings inside The battery itself has the problem of imbalance, which cannot be solved externally.

　　2. The principle of grouping the same type of batteries must be followed. Groups of batteries must be the same type of batteries, that is, the operating voltage range of the batteries must be the same. Batteries with different working voltage ranges cannot appear in the same battery pack, and cannot be mixed even if the capacity is the same.

　　3. If possible, the capacity, voltage and internal resistance should be measured before assembling the battery pack. Choose batteries with similar capacity and internal resistance as much as possible to reduce the expansion of consistency differences during reuse.

　　Since the capacity of the cascade battery is generally lower than the nominal capacity, in order to obtain sufficient capacity, a larger number of batteries need to be used to achieve the design capacity through suitable series and parallel connections, so they need to be assembled according to technical conditions.

　　Assembly method 1: Parallel first, string later, for example, battery packs used in electric vehicles use this method.

　　Assembly method 2: first in series and then in parallel, often used in data centers or computer rooms.

　　The two assembly methods have their own advantages and disadvantages, which are suitable for different environments:

　　Disadvantages of parallel first and then series: the selection of cell battery connection lines and busbars is very important, otherwise it will cause differences in battery charging and discharging, and individual battery leakage (or faults) will affect a parallel unit, which has a relatively large impact on capacity. Affect the battery life (mileage); advantages: easy to manage, if you add a battery equalizer, only one set (set) is enough.

　　The advantages of serial first and then parallel: convenient connection, convenient maintenance, rapid detection and handling of faulty batteries, easy maintenance, the capacity of the unit battery in each string can be different, the battery utilization rate is high, and the capacity (power) can be expanded and increased at will Backup time, improve reliability, especially suitable for data centers; Disadvantages: If you increase the battery equalizer, you need multiple sets (sets).

　　4. The following batteries cannot be reused: one is a battery with a large leakage current (or a high self-discharge rate); the other is a battery with a deformed appearance, such as a swelling shell; and the third is a battery with leakage.

　　Echelon battery equalization

　　Even if the selection of cascade batteries is very strict, it is difficult to guarantee the consistency of the batteries. Even if the batteries with excellent consistency are assembled together, there will still be different degrees of difference after dozens of charge and discharge cycles, and this difference will follow the use The extension of time gradually increases, and the consistency will become worse and worse. It is obvious that the voltage difference between the batteries is gradually enlarged, and the effective charging and discharging time is getting shorter and shorter. A large amount of test data found that battery packs with poor consistency have the following characteristics:

　　1. The voltage of the unit battery is obviously high and low, and the distribution is irregular;

　　2, the remaining capacity of the unit battery presents an irregular discrete distribution;

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

　　Through further statistics of test data, it is found that the biggest killer of battery imbalance:

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

　　2, violent charge and discharge, accelerate the expansion of the difference between batteries;

　　The capacity of the energy storage battery pack is very large. Taking the nominal 500Ah battery pack as an example, assuming that the difference between the maximum and minimum capacity of the battery is 50Ah, and the difference between other batteries ranges from 5 to 10Ah, the maximum effective discharge of the system The capacity is 450Ah (it is tentatively numbered as D battery, the same below), assuming a discharge current of 50A, the theoretical maximum discharge time is about 9h. After this time, the D battery will reach the discharge cut-off voltage and enter the over-discharge state. If it continues to discharge, it will seriously damage the D battery, and its maximum effective capacity will be sharply reduced, thereby further reducing the maximum effective capacity of the battery pack. There is also a problem of discharge rate. The discharge rate of the maximum capacity battery is 0.1C, the discharge rate of the D battery is 0.11C, and the discharge rate of other batteries is between 0.1C and 0.11C. The discharge rate is different, so The degree of attenuation of each battery is different, which will cause the difference and consistency of the battery to gradually expand and show an acceleration trend. Similarly, during charging, charge at a rate of 0.1C, the charge rate of D battery reaches 0.11C, which is at the maximum, and the charging limit voltage is reached first. Continued charging will enter the overcharge state, causing further damage to D battery, and other battery charge rates It is between 0.1C and 0.11C, and the difference in charging rate will aggravate the difference and consistency of the battery, and it will accelerate. Such a battery pack, after repeated charging and discharging, will eventually lead to smaller and smaller effective capacity and shorter effective discharge time. There is another serious problem with large-capacity energy storage battery packs, which is the risk of thermal runaway. For this battery pack, if effective prevention and control cannot be carried out, the D battery may become the highest temperature battery during the charging and discharging process of the battery pack. If a thermal runaway failure occurs, the battery may be completely scrapped, or even cause the battery pack to malfunction, or even more serious joint problems may occur, which I dare not imagine. If the battery pack can maintain each battery without overcharging and overdischarging during operation, the effective capacity and discharge time of the battery pack can be guaranteed, and it is always in a state of natural attenuation. It can be seen that battery balance is important for the battery pack. How important is normal and safe operation.

　　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 overall discharge time can exceed 9h, and Other batteries reach the end of discharge together, and overdischarge will not occur; similarly, if the 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 it will be automatically increased. The charging current of a large-capacity battery reaches the charging limit voltage together with other batteries, and no over-discharge occurs. It can be seen that the equalization current must be above 5A to meet the requirements, especially at the end of charge and discharge. From the principle of equalization, only the transfer type battery equalizer can be competent.

　　At present, the progress of effective battery equalization technology is very uneven, especially in equalization current and equalization efficiency. Although some solutions have adopted synchronous rectification technology, the maximum equalization current is mostly limited to less than 5A, and the continuous equalization current is only 1～3A, which is satisfactory. No need. Since it must support two-way balance, the current conversion efficiency is usually not high. The self-heating problem under a larger balance current is still prominent. Another important obstacle is the cost of equipment. Since most of the synchronous rectifier chips are used, the cost increases a lot.

　　High-efficiency battery equalization technology

　　At present, a high-power, high-efficiency, real-time, dynamic transfer battery equalizer technology has been successfully developed by Comrade Zhou Baolin of the Daqing City Transportation Bureau after many years. It takes the national patent technology (patent numbers 201220153997.0 and 201520061849.X) as the core, and incorporates the self-invented two-way synchronous rectification technology (patent applied: a transfer type real-time battery equalizer with two-way synchronous rectification function, application number: 201710799424.2), this is a two-way synchronous rectification technology that does not require a synchronous rectification chip, which not only greatly reduces the equipment cost, but also greatly improves the equalization current and equalization efficiency. A breakthrough in balanced technical indicators has been achieved, with the following characteristics:

　　1. Large balance current range. A large equalization current means that the equalization speed is very fast, see the attached table. At present, the enhanced lithium battery equalizer has realized that the relationship between the equalizing current and the voltage difference is about 1A/13mV. For example, when the voltage difference reaches 130mV, the equalizing current can reach about 10A, which is particularly conducive to high-speed equalization.

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

　　3, real-time dynamic balance. When the battery pack is in a static state, the maximum voltage difference in the pack can be controlled within 10mV or even smaller (depending on the setting of the reference voltage difference), and enter the micro-power standby detection state, whether the battery pack is in the charging state or in the In discharging state, once the voltage difference is detected to be greater than the reference voltage difference, it will immediately enter the high-speed equalization state. The biggest advantage of real-time dynamic equalization is that the effective equalization time is long, the efficiency of the equalizer is the highest, and its unique pulse technology has good maintenance and capacity for the battery The improvement effect has been tested by the application.

　　Using a high-current, high-efficiency battery equalizer can prevent the overcharge, overdischarge and thermal runaway faults of the attenuated battery to the maximum extent. Even if the capacity decay of the battery pack has formed the fact that the consistency has deteriorated, its decay speed can be reduced very well. By automatically forcing the voltage to maintain consistency, it can also increase the effective capacity of the battery pack to a certain extent and extend the battery pack’s The cycle life, in particular, significantly reduces repair and maintenance costs.