Lithium battery discharge test mode

　　The charging and discharge test equipment generally uses semiconductor devices as a stream element. By adjusting the control signal of semiconductor devices, it can simulate loads with different characteristics such as constant flow, constant pressure, and constant resistance. Lithium -ion battery discharge test mode mainly includes constant flow discharge, constant flux, constant power discharge, etc. Continuous discharge and interval discharge can also be distributed in each discharge mode. Among them, according to the length of time, the interval discharge can be divided into intermittent power discharge and pulse discharge. During the discharge test, the battery is discharged according to the set mode, and the discharge is stopped after the setting conditions are met. The discharge deadlines include setting voltage cuttering, setting time deadline, setting capacity deadline, and setting negative voltage gradient cutting. The change of battery discharge voltage is related to the discharge system, that is, the change of the discharge curve is also affected by the discharge system, including: discharge current, discharge temperature, discharge termination voltage; intermittent discharge. The larger the discharge current, the faster the operating voltage decreases; as the discharge temperature increases, the discharge curve changes relatively slowly.

　　(1) Hengli discharge

　　When the constant current discharge, set the current value, and then adjust the current value by regulating the CNC constant current source, so as to realize the battery constant current discharge.

　　At the same time, the end voltage of the battery is collected to detect the discharge characteristics of the battery. Hengli discharge is unchanged, but the battery voltage continues to decline, so the power continues to decline. Figure 5 is the voltage and current curve of the constant current discharge of lithium ion batteries. Due to the use of constant currents, the time coordinate axis can easily be converted to capacity (current and time multiplication) coordinate axes. Figure 8 is the voltage-capacity curve during constant current discharge. Hengli discharge is the most commonly used discharge method in lithium ion battery test.

　　(2) Constant power discharge

　　When constant power discharge, first set the power value P of the constant power, and collect the output voltage U of the battery. During the discharge process, the P is required to be constant, but U is constantly changing, so it is necessary to continuously adjust the current of the CNC constant stream according to the formula i = P / U to achieve the purpose of constant power discharge. Keep the discharge power unchanged. Because the voltage of the battery continues to decline during the discharge process, the current in the constant power discharge continues to rise. Due to constant power discharge, the time coordinate axis is easily converted to energy (power and time multiplication) coordinate axis. Figure 9 shows a typical constant power charging and discharge curve of lithium lys of lithium battery.

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