Studies have shown that as the number of battery charge-discharge cycles increases, the battery capacity decreases, the internal resistance of the battery increases, and the internal performance of the battery deteriorates until it finally fails. The process is a gradual accumulation process. The inconsistency in the battery pack will accelerate the battery pack. Enter an unsafe state.

　　A typical battery pack charge balance management system, its working method is to charge the connected series battery pack while detecting the terminal voltage of each single battery in the battery pack. When the terminal voltage of a single battery is high, The battery is charged and shunted by the equalization circuit connected in parallel with the single battery to reduce the charging speed and terminal voltage rise speed of the single battery, so that the terminal voltage of each single battery tends to be balanced and consistent, so as to avoid the series connection of battery packs. The difference in the charge and discharge characteristics of the individual cells in the battery affects the life of the battery pack. As the equalizing circuit connected in parallel with the single battery consumes part of the charging power during the charging and shunting, the equalizing circuit generates heat, and the equalizing ability of the equalizing circuit is limited. For large-capacity, high-power batteries, the equalization capability of the equalization circuit cannot meet actual needs when charging with large currents.

　　At the end of the battery’s life, the internal performance of the battery gradually deteriorates. If discharge or charge is performed according to the original discharge current limit value and constant current charge value, overdischarge and overcharge may occur, leading to further deterioration of battery internal resistance and other parameters. The battery will heat up severely during discharge and discharge. Although the existing BMS can monitor the abnormal increase in battery temperature and cut off the external charging or discharging path, the battery itself is already in an unsafe state, and cutting off the path cannot prevent abnormal electrochemistry inside the battery. During the reaction process, there is still a danger that the battery will continue to heat up or even explode. When the battery temperature rises abnormally, the discharge path is suddenly cut off, which may cause safety problems in the operation of the equipment for equipment that requires continuous power supply, such as electric vehicles.

　　Battery management system based on internal resistance measurement and status comparison

　　Studies have shown that as the number of battery charge-discharge cycles increases, the battery capacity decreases, the internal resistance of the battery increases, and the internal performance of the battery deteriorates until it finally fails. The process is a gradual accumulation process. The inconsistency in the battery pack will accelerate the battery pack. Enter an unsafe state.

　　This paper proposes a battery management system for internal resistance measurement and status comparison. As shown in the figure, the single-chip microcomputer is used as the control core, and the initial value of the internal resistance and the allowable error value of each single battery under different terminal voltages are stored in the memory in advance. During the process, the terminal voltage rise rate and error allowable value of each single battery in different terminal voltage sections, the predetermined value of the cumulative charge, the charge voltage range, the discharge voltage range, the charge cut-off voltage value, the discharge cut-off voltage value, the battery temperature range, Charge current value and charge current error allowable value, discharge current protection value, balanced starting voltage value, terminal voltage imbalance value and other parameters. During the charging and discharging process, various parameters of the charging and discharging process are detected, and the terminal voltage, terminal voltage rising rate, and charging current of each single cell in the battery pack are measured and recorded before, during and after the charging process. , Charge capacity and battery internal resistance, and compare it with the parameters measured and recorded during the previous charge, analyze the charge capacity of the battery pack and the changes in the internal resistance, terminal voltage, and terminal voltage rise rate of each single battery, and judge the internal battery The process and degree of performance degradation provide early warning of battery failure and possible safety issues. Control the charging and discharging process to realize charging and discharging termination voltage protection, temperature protection, and overcurrent protection. At the same time, during the charging process, the single battery with lower terminal voltage is compensated and balanced to make the series connection The terminal voltage of each single battery in the battery pack is the same to avoid the impact on the life of the battery pack due to the difference in the state of each single battery.

　　Schematic diagram of a battery management system with internal resistance measurement and status comparison functions

　　Using the system for the test of 10 20Ah series battery packs, using 5A constant current charging, 2A current compensation balance, the system compensation balance effect is very obvious, there is no additional heat, and it is convenient for energy saving control.

　　There are many factors influencing the change of internal resistance, especially the study of the internal resistance change law during the complete life cycle of the battery pack, which requires a lot of experiments. The relevant experimental plan is underway, including the entire discharge of the power battery pack under simulated working conditions. Life process testing.

　　in conclusion

　　Detect and record the battery charge, terminal voltage, current, internal resistance, battery temperature, charging time and other parameters during the charging process before, during and after the charge, and calculate the change amount and rate of change of each parameter, and Compare with preset initial parameters, accurately judge the degree of change in battery charging performance, and provide early warning of possible battery safety issues, providing high safety guarantee for the use of rechargeable batteries. Taking electric vehicles as an example, even if there is a battery safety warning, the driver has at least a few days of free time to repair and deal with it, without having to force it to disconnect immediately.

　　During the charging process, the single battery with lower terminal voltage is compensated and equalized, which reduces the status difference of each single battery and improves the service life of the battery pack, while avoiding the heating problem of the equalizing circuit during the charging equalization process. , Thereby greatly improving the balance ability, and has a significant effect on the application of large-capacity and high-power battery packs.

　　During the charging process, the battery charge capacity, terminal voltage, current, internal resistance, battery temperature, charging time and other parameters are comprehensively recorded during each charging process, thereby recording the change process of various electrical parameters throughout the life cycle of the rechargeable battery. Analysis of group failure causes provides a data basis.