9V rechargeable battery

　　Analysis of typical abnormal alarms of 9V rechargeable battery in energy storage power stations and research on corrective measures

　　As a new energy service product, energy storage is a high-quality, reliable millisecond-level control response resource. It can provide dual support of active and reactive power, and provide the power grid with a variety of services such as peak regulation, frequency regulation, backup, and accident emergency response, effectively meeting the needs of the power grid. The urgent needs for renewable energy consumption and safe operation of power grids promote the coordinated development of "source, grid, load and storage". In 2018, grid-side and user-side energy storage power stations began to be put into use. As the core component of energy storage power stations, batteries have also exposed some problems in actual operation. This article starts with the abnormality and alarm phenomena of the battery pack, conducts a comparative analysis on the design, selection and structure of the battery pack, and explores a safer, more reasonable and efficient battery pack design method.

　　1 Run data analysis

　　According to statistics on the operation data of a grid-side energy storage power station, there were a total of 31,435 battery alarm messages for the entire energy storage power station from January 8 to March 8, 2019, which had a great impact on the safe and stable operation of the power station (Table 1). Among them, a total of 31,313 cell overvoltage and undervoltage alarms were abnormal voltage alarms, accounting for 99.61%; a total of 60 overtemperature and undertemperature alarms were abnormal temperature alarms, accounting for 0.17%; and low SOC alarms were low battery charge. There were a total of 69 alarms, accounting for 0.22%.

　　Table 1 Statistics of actual operating alarm information of an energy storage power station

　　Considering that SOC alarms are caused by the inherent chemical characteristics of lithium batteries, this article focuses on the analysis and research of abnormal voltage and temperature alarms.

　　2.1 Abnormal voltage

　　2.1.1 Analysis of abnormal causes: The connecting bolts of the main positive and negative aluminum rows of the aircraft plug and the U box were not locked according to the torque requirements when they left the factory, resulting in increased contact resistance and battery voltage sampling errors; the total positive and negative aluminum rows of the aircraft plug and the U box The connecting bolts of the negative aluminum row are not anti-vibration/relaxed. In addition, the battery box vibrates or expands due to thermal expansion and contraction during long-term operation, causing the connecting bolts to loosen and the contact resistance to increase (single alarms sometimes appear irregularly, (Some occur repeatedly); false welding and missing welding lead to changes in contact resistance; the internal modules of the U box use welded aluminum rows for split type, that is, each module uses an aluminum row for welding, and the aluminum rows between modules are close to each other. For screw connections, the screws are not locked or are loose due to long-term vibration/thermal expansion and contraction, causing the contact resistance to increase. The connection of some aluminum bars is unreliable, and the contact resistance increases due to dust entering during operation; there are differences in the consistency of the battery cores, and the internal resistance increases due to the attenuation of the battery itself or long-term operation; the aviation plug withdraws the pin, causing vibration or heat Under the action of expansion and contraction, the aviation ferrule body is prone to pin withdrawal, resulting in poor contact, resulting in increased contact resistance, which in turn causes an increase in voltage drop. From the disassembled old aviation plug, it can be seen that the core body is easy to pull out, and there are obvious signs of oxidation in the connection between the core body and the aluminum row.

　　2.1.2 Rectification plan: Replace the bolts connecting the positive and negative aluminum rows of the U box with the aviation plug to anti-fall bolts, coated with anti-fall thread adhesive, and locked with a torque of 10N·m; after replacement, measure the internal resistance with a voltage meter The internal voltage resistance of the module and the impedance between the total positive and total negative aluminum bars and the aviation plug. If the impedance is ≤0.2mΩ, it is considered qualified. If it is not qualified, check and tighten the bolts to check whether there is any false welding. Remove the connecting bolts of the aluminum row of the module and clean the surface of the aluminum row with alcohol. Measure the module voltage and compare it with the entire cluster. If the voltage difference is within 200mV, it is considered qualified. Otherwise, the module will be recharged or discharged.

　　Testing and comparison of new power connecting lines found that the new structure is conducive to reducing the internal contact resistance and can reduce the voltage drop and temperature rise problems caused by excessive contact internal resistance. The SIA plug structure was tested on a charger and discharge machine with a current of 150A, and the voltage drop and actual current were recorded. After data calculation, the internal resistance of the SIA plug and copper bar combination was between 0.073~0.093mΩ.

　　2.2 Temperature anomalies

　　2.2.1 Cause analysis: The air duct structure is unreasonable. Through thermal simulation data analysis of the air duct, it was found that the wind speed at the end of the air duct was basically 0, the air volume was also very small, and the cooling effect was not achieved; the U box fan did not start. Starting the fan can accelerate the air flow rate and achieve a certain cooling effect. However, because the BMS (battery management system) sets the fan starting temperature to be too high (40°C), the U box fan does not start; the spacing between individual cells in the U box is relatively small. Small, which is not conducive to ventilation and cooling; the air duct is not tightly sealed at the upper end of the air conditioner outlet, and there is a gap at the joint between the air conditioner outlet and the air duct. There is an obvious feeling of wind blowing when the hand is stretched here, and there is air leakage, causing wind pressure, Air volume loss.

　　2.2.2 Rectification plan air duct rectification. Use special-shaped sheet metal parts and foam as shown in Figure 3 to install them at the air duct outlet (near the air-conditioning outlet). By narrowing the air duct outlet, the air pressure is increased and the flow rate of cold air/hot air in the air duct is increased to ensure that the air is at the end of the air duct. (Cluster 5 and Cluster 1) have a certain air volume to improve the cooling effect. Judging from the test results on the A side of cabin 13#, the wind speed and air volume at the end of the air duct have improved, but the effect is not obvious enough. Further analysis and communication with operation and maintenance personnel revealed that the U-box fan did not start during operation. If the fan is started, it can further accelerate the flow speed of the wind and the cooling effect will be further improved [2].

　　Fan startup strategy optimization. Adjust the fan control strategy and change the fan starting temperature to ensure that the U box fan starts to meet the U box heat dissipation requirements.

　　3. Analysis of the rectification effect. After the energy storage power station was rectified and re-operated for a week, the operation data was collected and the rectification effect was analyzed. Voltage test. Select the No. 23 battery compartment, charge or discharge at full power (500KW), record the cross-contact voltage distribution, and compare the BMS system data before and after the rectification. It is found that the cross-contact voltage discreteness disappears after the rectification, and the BMS no longer reports voltage abnormalities. Impedance testing. Select the No. 23 battery compartment, replace the bolts, re-tighten the torque, and use an internal resistance tester to confirm the impedance of all connection points (Figure 4). All impedances are controlled within 0.25mΩ.

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