Author ：Iflowpower – Portable Power Station Supplier
Dynamic lithium-ion battery management system Design Method: This paper discusses the design method of dynamic lithium-ion battery management system to achieve overcharge protection, over-discharge protection, overcurrent protection and equalization of lithium-ion battery powered lithium battery packs. Keywords: lithium-ion power lithium battery pack; management system; overcurrent; over-discharge; overcharge; balance control Introduction to the wide use of lithium-ion batteries for more than ten years, but early important for mobile phone, laptop, camera, DVD Waiting for a series of small mobile electronic products, these occasions tend to be single-use, low load current, high safety factor. In the past two years, lithium-ion batteries have begun to use quickly, high-energy density, non-pollution, etc.
, has begun to be used quickly on electric bicycles, electric tools, and power toys, and gradually use for hybrid vehicles and electric vehicles. However, the safety of the dynamic lithium-ion battery is still the problem that people are currently most concerned, so they are very important for their protection. In addition to ensuring continuing to improve the safety of lithium-ion batteries, it is not possible to study the management system of the battery, so that the battery and its use can be balanced.
Protection of lithium-ion batteries Important includes overcharge protection, over-discharge protection, overcurrent and short circuit protection, etc. 1 Function 1.1 Overcharger Protection For the lithium ion battery, the maximum voltage of the single-section battery cannot exceed the specified value after charging, otherwise the electrolyte in the battery will be analyzed, so that the temperature rises and germinate gas, reducing the battery.
The service life is severe, and even cause an explosion, so the protection circuit must ensure that the end voltage of each battery in the battery pack is absolutely inexhaustible. When the voltage of the battery exceeds the set value, it is activated. Charging protection function, cut off the charging circuit by the protection circuit, suspend charging.
The protection can be stopped when the battery voltage returns to the permitted voltage and releases the excess lock mode. Lithium-ion batteries of different materials have their own different specified values. In addition, it is not necessary to pay attention to the misunderstanding of the noise, in order to prevent misconduct and misoperation, it is necessary to set an overcharging delay, and the delay time cannot be shorter than the noise.
When the voltage continues to exceed the overchalton test voltage, it will trigger an over-reserve protection. 1.2 Over-discharge protection of the excessive discharge of the lithium-ion battery will shorten its life, and damage to the battery is often irreversible.
In order to prevent the over-discharge state of the lithium ion battery, when the lithium ion battery voltage is lower than its over-discharge voltage test point, the over-discharge protection, the discharge is activated, and the battery is maintained at a standby mode of low static current, and the parameter setting is similar. Charge. 1.
3 Excessive / short-circuit protection Lithium-ion battery has certain limitations, excessive discharge currents can also cause irreparable damage to lithium ion batteries, affecting their service life. The feature of short circuit protection is actually expanded over flow protection. If the externally short circuit is caused, the discharge is stopped immediately, otherwise it may cause serious damage to the lithium ion battery itself and external equipment.
The delay time of overcurrent protection is generally at least a few hundred microseconds to milliseconds, while the short-circuit protection delay time is microseconds, almost short-circuit instantly cuts the loop, which can prevent huge damage to the battery from the battery. In terms of power tools, the setting of the protection current value and the delay time is not combined with the parameters of the power tool itself, otherwise it will affect the output torque of the tool and the life of the motor. 1.
4 Battery balanced dynamic lithium-ion batteries generally have a few strings, dozens of strings or even hundreds of strings, due to the battery in the process of processing, it is necessary to pass a lot of steps from the coating film to become a finished product, even after a strict test procedure, The voltage, resistance, capacity of the power supply is consistent, but after a period of time, the internal resistance, voltage, capacity, etc. are born, form an inconsistent state, will be born or such differences. This difference is reflected as the voltage between the series battery cores when the battery pack is overflowed or after.
In this case, during the battery pack, the battery core is too high, and the battery core is triggered early, and the battery core that is too low in the discharge process causes the battery pack to over-discharge protection, thereby enabling the overall battery pack The capacity is clearly lowered, and the capacity embodied throughout the battery pack is the capacity of the battery core in the battery pack, and it is easy to overcharge and excessive phenomenon during use, and it is not easy to discover, resulting in advance failure. Therefore, the protection circuit can be used to complete the balanced operation of the battery unit to extract excess current from a battery having a higher voltage, consume extra power, realize battery equilibrium, maximize the utility of dynamic lithium-ion batteries, and extend battery use Life, new security. The commonly used equalization method has energy storage equilibrium and resistance balance.
The energy storage equilibrium is the charge and discharge of the energy storage element such as inductance or capacitance to achieve energy transfer between the energy transfer between the battery. This balanced charging method generally controls the complex network of networks, high security management requirements, should pay attention to the charging and discharge time of energy storage components, and the maximum advantage is that all units can be balance each unit. The function of the battery does not consume the electrical energy of the lithium ion battery pack.
Resistance equalization is generally transmitted to battery packs through the controller control resistor network, which can be balanced for multi-cell batteries at the same time. However, in the equalization process, if the electrically resistant is too small, the equalization current is too small, the effect is very small; if the electrical resistance is too small, the resistance power is large, the system energy loss is large, the balance efficiency is low, the system is high for heat management requirements. To perform temperature test control.
The principle of resistance equalization is in the process of battery pack charging, when a certain battery is faster, the voltage is higher than other batteries, the system is controlled by controlling the power-on shunt of the equalization resistance, and the battery is charged to reducing the charging speed of the battery to achieve each section. Battery balance charging purpose. 2 Protection function Realization of the protection of lithium-ion batteries Important: single-chip control and integrated circuit protection chip.
2.1IC Control Currently, there are many chips that can realize lithium-ion battery protection. There are many kinds of chips, Taiwan, and mainland can choose.
At present, there is a lot of ways to use, mature, and the peripheral circuit is simple, but the price is comparison expensive. The functionality of various protection ICs is different. The protection mode and external lines are also different.
It can be based on different ICs in actual use. When choosing an IC, it is necessary to consider it. The overcharge protection voltage of different models of IC is different.
There are 4.25V and 4.35V, and the IC's own power consumption, the peripheral circuit is simple enough, protect the parameters of IC Is it in line with the requirements, the volume is small enough, you must consider thoughtful.
In addition to the protection of the protection, the protective plate is also a critical parameter. For the over-discharge of the alert, protect the IC to test the battery voltage. Once the over-discharge test voltage is reached, it is not to turn off the power MOSFET and the cut-off discharge.
However, at this time, the battery itself still has a natural discharge and the current consumption of the IC. Therefore, it is necessary to reduce the current consumption of the IC to the lowest level, and when the statically consumption current is not 0.1ua.
In addition, the power lithium-ion battery is working or charging, and there will be high pressure gerberations. Therefore, the protection of ICs should meet high pressure requirements. Figure 1 is a schematic diagram of 4 string usage schematic to protect the IC in the Seiko S-8254A.
The S-8254 series built-in high precision voltage test circuit and delay circuit are ICs for 3 sections or 4-segment-linking lithium ions or lithium polymer rechargeable batteries. Switching through the SEL terminal, can be used to protect 3 or 4 series battery cells. Figure 1S 1S-8254A4 String Protection Schematic Schematic The current battery protection chip can generally protect 4 lithium-ion batteries, but many of the lithium-ion batteries above 5 sections, such as electric tools, electric bicycles, and UPS, at this time What should I do? As shown in FIG.
2, the circuit can realize the output power of 20A / 24V, so that S-8254AAV is used as a use example of the control chip, which simultaneously uses two protective chips together, protects the 8-string lithium ion battery pack, over The deprotection voltage is 2.70V ¡À 0.080V, the overchaulic voltage is 4.
250V ¡À 0.025V. Figure 28 Servatic Lithium Ion Battery Protection Circuit This circuit equilibrium control uses R5408 chip, the voltage measurement accuracy is relatively high, and the equalization current is up to 1A.
2.2MCU Controls Existing Integrated Circuit Protection Chips Important to the protection of battery packs below 4, and battery packs above 4 sections can be used in series or several multi-level protection of multiple single-stage protection chips. Way of chip series.
However, the circuit scalability of the battery pack of the 4-section battery pack using a plurality of protective chips. At the same time, integrated protection chips are often only for one or one of the characteristics of a type of battery, and the cost is often relatively high. To this end, combined with the charging and discharge characteristics of the lithium ion power lithium battery, many cases of power lithium ion battery protection circuits, design methods using MCU (micro-conscious) as the core.
As the core of various functional controls, the micro-rescue is supplied to the lithium-ion battery pack to provide overcharge, overlapping, overcurrent protection. Protection, short circuit protection, while supplying functions such as capacity prediction, communication, identity identification. 3 Hardware anti-interference measures power lithium ion battery management system as part of the use system, often subject to various electromagnetic interference, the actual working environment is more bad, it is necessary to take certain resistance on hardware design and PCB board Interference measures.
4 Other Requirements Because the battery is important to supply power to the main use project, it requires BMS only very low power consumption. 5 Monitoring of the end of the dynamic lithium-ion battery pack is a newest issue, and its management system will integrate monitoring of technical design ideas, with basic functions such as static, charging, discharging, management, automatic maintenance of battery packs, and achieve practicality, Reliable use requirements.
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