Safety Management of Lithium Battery Pack-SOC

The safety management of lithium battery pack-SOC also has a DOD (depth of discharge) corresponding to SOC. This parameter refers to the percentage of the current released power to the total capacity, which can be used for the BMS to correct the actual capacity of the battery. Unlike SOC, DOD can exceed 100%. In short, the measured voltage budget SOC in BMS accounts for the majority; in electric vehicles, integration is often added. In advanced applications, in order to improve the budget accuracy of the SOC, methods such as Kalman filtering and neural networks are also introduced, which can adapt to actual conditions. The internal resistance of a battery is difficult to directly measure, and it will vary with changes in factors such as battery state of charge, temperature, and discharge rate. However, there is still a certain correspondence between internal resistance and SOC. The method of DC measurement of internal resistance is to instantaneously change the current, measure the voltage, and the ratio of the momentum of the voltage change to the momentum of the current change is the battery internal resistance. The method of internal resistance is very messy, and the practice is not too much. There is a third method of internal resistance: integral method (ampere method) because energy is conserved, so the amount of electricity released when the battery is charged is the same as the amount of electricity released when it is charged. The method of integrating charging power and time to obtain charging power, and integrating discharging power and time to obtain discharge power is more commonly used in commercial electric vehicles. But there is another problem: there are too many measurement parameters involved, especially the initial SOC with budget will have a significant cumulative error. The accuracy of the measurement voltage, current and other wheel parameters is very high. At different charging and discharging rates, the impact of battery resistance is Batteries that cannot be handled will gradually age, and their capacity will change. During the charging and discharging process, the relationship between the electromotive force and the state of charge is mostly a monotonic function, and the corresponding state of charge can be obtained by measuring the electromotive force. This is a lithium manganate battery的charge-discharge curve. However, this method has some obvious shortcomings: the curve here is a description of electromotive force, when there is current flowing, the battery resistance will make the measured voltage and electromotive force opposite, the greater the ignition error, the greater the current, the greater the error. There is such a strange battery in the process of charging and discharging, a large piece of lithium iron phosphate battery is basically in a constant voltage state, close to a single value function, no matter how accurately the voltage is measured, it cannot correspond to the correct degree of SOC thinking. Two ways: directly measure the voltage state of charge as the percentage of the remaining battery. This parameter has two meanings: about a single battery, or about a battery pack. The budget of a single SOC is accurate, and can be used to adjust the balance of the battery pack to make the situation of each battery consistent; the SOC budget of the battery pack is accurate, and it can accurately display the remaining power and look forward to the user experience. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: What are the unique advantages of lithium batteries?