First, the AC method to measure the internal resistance of the battery Currently, the measurement instrument used in the battery is commonly used in the AC injection method or the DC instantaneous discharge measurement method. Instruments that use AC injection, such as instruments that measure impedance or conductance, apply an AC test signal to the battery during measurement, and then measure the corresponding voltage, current, and impedance readings. V/I varies with frequency. Anti-XC also makes the electrochemical resistance RE smaller. Instruments using AC mode are subject to interference from charger ripple current and other noise sources. Some devices cannot be tested online (connecting charger and load and floating state). The frequency is 60Hz or 50Hz. AC test currents are less desirable because they are the primary frequency of charger ripple and noise sources, and it is not uncommon to have RMS ripple currents greater than 30A on large UPS battery packs. At present, large-scale UPS and high-frequency UPS applications are becoming more and more popular. It is very common to have strong ripple interference on the battery, especially on UPS systems such as Emerson, Schneider and Eaton. The following is a description of the ripple interference of a foreign manufacturer that uses the AC method to monitor the internal resistance of the battery.
  The text section describes how the ripple on the battery interferes with the battery monitoring device: In a UPS system, the inverter generates 2, 4, and 6 ripple currents during the inverter process. This ripple current It will be poured into the battery. Because the equipment that monitors the internal resistance of the battery by AC method needs to inject an AC signal into the battery during testing, this AC signal will be disturbed by this ripple, causing measurement error.
  In the table, the influence of the ripple of different frequencies on the internal resistance measured by the AC method is specifically listed: when measuring 12V battery, the ripple current of 50HZ frequency/1A, the influence of multiple harmonics on the measurement accuracy of the monitoring equipment is 1.3. % 4.1% 0.7% = 6.1%. In many large UPS systems, the ripple is much larger than 1A. Therefore, the measurement of battery internal resistance by AC method is often not applicable in large UPS systems and high frequency UPS.
Second, the DC method to measure the internal resistance of the battery
  The method of measuring internal resistance using DC instantaneous discharge is to generate a transient load current from the battery pack and then measure the instantaneous change of the voltage on the battery pole. It can be deduced by the instantaneous voltage drop when the load is turned on and the instantaneous voltage recovery when the load is disconnected. Corresponding internal resistance. Current A/D converters can ignore the AC signal flowing through the battery while effectively measuring DC parameters, so this type of instrument can even test the battery online in a noisy environment.
  The working principle is to divide a group of battery components into multiple cycles, and each time the internal resistance is measured, the first cycle is discharged, and then the second cycle is discharged until the last cycle. At the same time of discharge, the system collects the discharge curve of each cell (or each group) at high speed, and measures the internal resistance of each cell after obtaining the voltage drop. The discharge load uses a constant current load to ensure that the current per discharge does not change when the voltage changes.
   The system can be set to automatically measure the internal resistance at regular intervals without manual intervention.
  Therefore, the advantages of this measurement method are: ◆ Automatic measurement without manual intervention;
                            ◆ Strong anti-UPS interference, accurate and fast;
                            ◆ safe and reliable;