Application of Equalizer Technology in Storage Battery

　　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 supercapacitor 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 supercapacitor packs.　　Echelon battery and selection 　　Echelon battery refers to the battery that has been used and reached the original design life, and its capacity is restored in whole or in part by other methods.　　 Generally used 5 years later, its effective capacity is about 80%. The natural decay of the battery enters a stable period, and it can be used as a small-capacity battery. Through the parallel use of a certain number of batteries, the available capacity can be increased by several times, which fully meets the needs of energy storage and power. , 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 the batteries in a battery pack need to be replaced, but the capacity of one or several batteries is seriously attenuated. The entire battery pack is affected. If there are multiple such battery packs, the severely attenuated battery can be removed through detection, and the other batteries can be reused in cascades through the capacitance and internal resistance detection. 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 closed loop of the power battery industry chain, and it has important value in environmental protection, resource recovery and improving the value of the full life cycle of power batteries. After retired power batteries have undergone testing, screening, reorganization and other links, they are still capable of being used in low-speed electric vehicles, backup power supplies, electric energy storage and other fields with 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. Body lead-acid batteries, various lithium batteries, including lithium iron phosphate batteries, lithium titanate batteries, ternary lithium batteries, lithium cobalt acid batteries, lithium manganate batteries, etc. 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 the internals of these batteries are multiple strings 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 they cannot be mixed even if the capacity is the same.　　3. If possible, the capacity, voltage and internal resistance of the battery pack should be measured before assembling. Choose batteries with similar capacity and internal resistance as much as possible to reduce the expansion of consistency differences during reuse.　　Because the capacity of the cascade battery is generally lower than the nominal capacity, in order to obtain sufficient capacity, it is necessary to use a larger number of batteries to achieve the design capacity through appropriate series and parallel connections, so it needs to be assembled according to technical conditions.　　Assembly method 1: Parallel first, string later, such as battery packs used in electric vehicles.　　Assembly method two: 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 first parallel and then string: the selection of unit battery connection lines and bus bars is very important, otherwise it will cause differences in battery charging and discharging, and individual battery leakage current (or failure) Affecting a parallel unit has a relatively large impact on the capacity, which directly affects the endurance (mileage); advantages: easy to manage, if you increase the battery equalizer, only one set (set) is needed. 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 the battery with large leakage current (or high self-discharge rate); the other is the battery whose appearance is deformed, such as the outer casing swelling; and the third is the battery with leakage. Even if the screening of the cascade battery is very strict, it is difficult to ensure the consistency of the battery. As the use time increases gradually, the consistency will get worse and worse. It is obvious that the voltage difference between the batteries gradually increases, and the effective charge and discharge time becomes shorter and shorter. A large number of test data found that the battery pack with poor consistency has the following characteristics: 　　1, the voltage of the unit cell is obviously high and low, irregular distribution; 　　2, the remaining capacity of the unit cell shows an irregular discrete distribution; 　　3, the unit cell The size of the internal resistance also presents an irregular discrete distribution. Through further statistics of the detection 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 Differences between batteries; 　　2, violent charge and discharge, accelerate the expansion of the difference between batteries; 　　The capacity of energy storage battery packs is very large, taking the nominal 500Ah battery pack as an example, assuming that the difference between the maximum capacity and the minimum capacity of the battery is 50Ah, other The difference between the batteries ranges from 5 to 10Ah, the maximum effective discharge capacity of the system is 450Ah (tentatively designated 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 charging rate of D battery reaches 0.11C, which is at the maximum, and the charging limit voltage is reached first, and continuing to charge will enter the overcharge state, causing further damage to the D battery, and other battery charging rates. It is between 0.1C and 0.11C, and the difference in charge 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 overcharge and overdischarge 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. 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 balancing technology is very unbalanced, especially in terms of balancing current and balancing efficiency. Although some solutions have adopted synchronous rectification technology, the maximum balancing current is mostly limited to 5A, and the continuous balancing current is only 1 to 3A, which is satisfactory. No need. Due to the need to 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. Because 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 type battery equalizer technology has been successfully developed by Comrade Zhou Baolin of Daqing 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. It has achieved a breakthrough in the equalization technical indicators, and has the following characteristics: 　　1, a large equalization 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 equilibrium 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 group 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 the discharge 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, and the efficiency of the equalizer is the highest. 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 capacity. The cycle life, in particular, significantly reduces repair and maintenance costs.　　 Actual use effect: use on 24 strings of monomer 2V170Ah lead-acid battery packs returned to the factory by customers. Using standard 17A current charging and discharging, without equalizer, the maximum discharge time after full charge is about 3h. During the discharge of the 3 batteries, the heat is serious, and the voltage value is less than 0.5V, and the voltage value of 1 battery is -0.1 V, polarity reversal occurred. The voltage of 21 batteries ranges from 1.8V to 2.0V, and there is still a lot of power that has not been released; after using the battery equalizer prototype in this article, under the standard charge and discharge parameters, after a few charge and discharge cycles , The discharge time is gradually extended to about 5.5h, and the efficiency is improved by more than 80%. The voltage of the three worst batteries after discharge is all above 1.5V, and the discharge voltage gradually rises, especially the serious problem of heat at the beginning. Great improvement, the temperature drop is very obvious, only the voltage of 4 batteries is around 1.9V, and the other batteries are around 1.8V, the battery power is fully and effectively released.