Charging method based on high voltage lithium ion battery pack


  Author :Iflowpower – Portable Power Station Supplier

The general series charges currently charges the charging of the lithium-ion battery packs, which is constructed in series, which is to be due to the simple structure of the series charge, low cost, and easier to implement. However, due to differences in capacity, internal resistance, attenuation characteristics, self-discharge between monomer lithium ion batteries, the single cells in the battery pack will be smaller in the battery pack. The first grain, at this time, other batteries have not yamped electricity, if they continue to charge, the inert-lithium-ion battery may be overchargeable.

The lithium-ion battery overcharge will seriously damage the performance of the battery, and may even lead to the injury of the explosion. Therefore, in order to prevent the monomer lithium-ion battery overcharge, the lithium ion battery pack is generally equipped with a battery management system (BatteryManagementSystem, Abbreviation BMS), controlling each single lithium ion battery by battery management system. When charging is charged, if there is a single-lithium-ion battery's voltage to reach the charge protection voltage, the battery management system cuts off the entire series charger, stop charging, and the single battery is overcharge, which will result in other Lithium ion battery cannot be inevitable.

After years of development, lithium iron phosphate dynamic lithium-ion batteries have substantially meet the requirements of electric vehicles, especially pure electric cars due to high safety, very good cycle performance, and have basically available. Processing conditions. However, the performance of the lithium phosphate ion battery has a certain difference between the other lithium ion batteries, in particular its voltage characteristics and lithium manganate, lithium-ion battery, etc.

The following is a comparison of the charging curve of lithium iron phosphate and lithium-manganese acid 2 lithium ion batteries and lithium ion delinement corresponding relationship: 1 lithium ion-ion battery lithium ion deinterlection and charging curve correspondence Figure 2 Lithium iron ion battery The corresponding relationship between the lithium ion desertification and charging curve is not difficult to see from the graph of the above figure. When the lithium ion battery of the lithium phosphate is overflowing, the lithium ions are almost completely removed from the positive electrode to the negative electrode, and the battery terminal voltage rapidly increases, and the charging curve The upward phenomenon, which will cause the battery to be easily reached the charge protection voltage. Therefore, the phenomenon of certain batteries in the lithium iron phosphate ion battery pack is more distinct.

In addition, although some battery management systems have equalization, due to various aspects of cost, heat dissipation, reliability, the balanced current of the battery management system is generally much smaller than the current of series charging, so the equalization effect is not very clear, it will also appear Some monomer batteries are dissatisfied, which is more distinct to the lithium-ion battery pack to be high current charging, such as the lithium ion battery pack for electric vehicles. For example, 100 discharge capacity is connected in series to constitute a battery pack in series, but if a group is set, 99 monomer lithium ion battery charge 80ah, another monomer lithium ion battery charge 100ah, When this battery pack is connected in series, the monomer lithium-ion battery in which the charge 100ah will be filled, thereby reaching the charge protection voltage, in order to prevent this monomer lithium ion battery is overcharged, the battery management system will The entire series charger is cut off, so that other 99 batteries cannot overflow, so that the entire battery pack discharge capacity is only 80AH. General battery manufacturers are probing capacity when the battery is factory-in-factory, and the constant flow is charged and recharged.

Then constant current is discharged to measure the discharge capacity. General discharge capacity is about equal to constant current charging capacity plus constant pressure charging capacity. In the actual battery pack series, there is no constant voltage charging process in the series of battery packs, so the constant voltage charging capacity will not, the battery pack capacity will be smaller than the single battery capacity.

The smaller the charging current, the smaller the constant voltage charging capacity, the smaller the capacity of the battery pack loss, so the battery management system and the charging machine coordinated with the series chargeable mode. Battery management system and charging machine coordination with series charger management system is the most comprehensive device for the performance and state of the battery, so connect the battery management system and charger to make the charging machine real-time information about the battery. It is more effectively handling the battery when the battery is charged, and the schematic is as follows.

Figure 3 Power Lithium Ion Battery System Integration Method Figure 4 Lithium Ion Battery System Basic System Figure 5BMS and Charity Coordination Teamwork Concharge Schematic Simple Map Battery Management System and Charging Motor Coordination The principle of charging mode is: Battery management system passed the battery Current status (such as temperature, single battery voltage, battery operating current, consistency, etc.) to monitor, and use these parameters to estimate the maximum allowable charge current of the current battery; during charging, battery management The system and charger are linked to realize the sharing of data. The battery management system transmits the total voltage, the highest single battery voltage, the highest temperature, temperature rise, maximum allowable charging voltage, the highest number of monomer battery voltage, and the maximum allowable charge current to the charge machine, and the charger can be based on the battery Manage system supplies changes their charging strategies and output currents.

When the maximum allowable charge current supplied by the battery management system is high in the current capacity of the charger, the charger is charged according to the maximum output current; when the voltage of the battery, the battery management system can test and promptly notify charging in real time. Machine change current output; when charging current is greater than the maximum allowable charging current, the charger begins to follow the maximum allowable charging current, which effectively guards the battery overcharge and reaches the purpose of extending battery life. Once the charging process, the battery management system can set the maximum allowable charge current to 0, forcing the charging machine to stop, alert accident, and ensure the safety of charging.

In this charging mode, the management and control functions of the battery management system can be improved, and the charger can change the output current in real time in accordance with the state of the battery, and all batteries in the hot battery pack, and optimize charging. The actual discharge capacity of the battery pack is also greater than the general tandem charging method, but this approach is to deal with some of the battery packages in the battery pack, especially when the number of battery packs, poor battery, and charging current Big time. Parallel charge to solve some of the problems of certain monomer batteries in the battery pack, and develop a method of concurrency charge, the schematic is as follows.

Figure 6 Connected to the conferences but concurrently with multiple low voltages, the high-current charging power supply is charged for each single battery, the presence is high, the reliability is low, the charging efficiency is low, the connection line is thick Waiting for defects, there is no wide range of charging methods in a wide range. The series large current charging plus small current parallel charge is a certain problem due to the above three charging methods. I developed a charging approach to high voltage battery packs, especially electric vehicle battery packs, that is, battery management systems and charging.

Machine coordination with a series of parallel small current charging of the large current charging plus constant pressure limit, the schematic is shown below. Figure 7 Battery management system and charging machine coordination with series charge plus combined charging schematic diagram This charging method has the following features: (1) Since the BMS of this system has the function of overcharge, thereby ensuring that the battery does not appear over charge. Of course, if BMS cannot communicate and control with the parallel charge power supply, since the constant voltage value of the parallel charge power supply is generally the same as the voltage value of the monomer lithium ion battery in the lithium ion battery pack, there is no overcharge problem.

(2) Since it is possible to perform parallel charge, do not reliability, relatively high balanced circuit, and the charging effect is better than the series charging method with a balanced circuit, and its maintenance management is simple and easy. (3) Since the maximum current of the series charge is larger than the current of the converged electricity (generally more than 5 times), it can ensure that the higher capacity is charged in a shorter time, thereby exerts the maximum effect of series charge. (4) When charging, the order of series charge and parallel charge and the quantity of the parallel charge power supply can be flexible, and charging can be performed simultaneously; it can be charged in parallel, and it can also be used in parallel charging; or use a parallel charge power source according to the voltage in the battery pack.

The situation is currently charged by the lowest battery. (5) With the development of technology, the parallel charge power supply can be a non-contact charging power supply (wireless charging power) or solar cell power supply, so that the parallel charge is simple. (6) When the number of monomer lithium ion batteries in the lithium ion battery pack can divide a lithium ion battery pack into several lithium ion battery pack modules, and the BMS and charger coordination are coordinated with BMS and charger.

Charge is charged in a manner in combining a caliber-based small current charging of constant voltage current limiting. It is desirable to reduce the number of series batteries in the battery pack, and the consistency between the monomer batteries is relatively poor, resulting in a shortcoming of the charging effect of the BMS and the charging machine to coordinate the charging effect in order to exert BMS and charger. Coordinate the maximum effect of coordination charging mode.

This approach is especially suitable for high voltage battery packs that consist of a fast replaceable low voltage (e.g., 48V) battery module system, so that charging or repair can be performed in parallel with battery replacement station or charging station (general user usually charges Can not be used in parallel with a parallel charge, and is sorted and re-enrich it according to the actual situation.

The charging method with the battery management system and the charging machine coordination with the series major current charging plus constant pressure limit flow can effectively handle the lithium-ion battery pack series with the overcharge, filled, dissatisfied, etc., and can be guarded The charging power supply is high, the reliability is low, the charging efficiency is low, the connection line is thick, etc. is currently the most suitable for high voltage battery packs, especially electric vehicle battery packs.

Conclusion Lithium-ion battery is an ideal power supply due to high operating voltage high, small size, light quality, no memory effect, no pollution, self-discharge, long-circulating life is an ideal power supply. In actual use, in order to obtain a higher discharge voltage, at least two monomer lithium ion batteries are generally formed in series with lithium ion battery packs. At present, lithium-ion battery packs have been widely used in laptops, electric bicycles, and spare power and other categories.

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