The power battery pack charging and discharging testing system can meet the various standard testing requirements of power batteries, with rich programmable functions and expandable functions, while considering ease of use, reliability, and safety. It is a high-precision charging and discharging equipment specially developed for high-power secondary battery pack testing, which recycles and reuses the electrical energy generated by battery pack discharge, and provides high-precision output measurement, suitable for detection that requires reliable data. The system adopts high-power IGBT control technology to achieve bidirectional AC/DC conversion, meeting the requirements of high standard testing specifications. It can achieve simulation testing of charging and discharging of power battery packs under various working conditions, comprehensively evaluate the capacity, efficiency, state of charge, thermal performance, and other performance of the battery pack, providing reliable guarantee for the production of power battery packs. The system has the characteristics of energy feedback function, high conversion efficiency, low grid connected harmonics, high efficiency and energy saving, no pollution to the power grid, fast dynamic response time, etc. It will not cause environmental temperature rise during the testing process, and the equipment operates reliably.
System architecture composition
Equipment technical parameters
1)DCIR testing
The evaluation method of DCIR is based on the spirit of BS EN61960, and this test waveform can be used to calculate the DCIR value using voltage difference.
Calculation method 1: Apply a current pulse at both ends of the battery, and the voltage at the battery end will undergo a sudden change, where: Δ I is the current pulse; U (t) is the battery terminal voltage at time t; U0 is the initial battery terminal voltage. DC internal resistance often includes ohmic internal resistance and a portion of polarization internal resistance, where the proportion of polarization internal resistance is affected by the current loading time t. Calculation method 2:When a current is applied at both ends of the battery to jump to another current value, the voltage at the battery end will change, where: Δ I is the current change value; Δ U is the voltage change value.
2)Battery pack cycle life test
The charging and discharging service life of a battery is not only required for power batteries, but all battery cell products have the same testing conditions. The testing is based on the charging and discharging conditions defined by the assessor as a cycle, repeatedly testing the same battery cell, evaluating the battery until the testing termination conditions are met, and correctly performing several cycles, that is, the cycle of this battery. The more cycles there are, the longer the lifespan of the battery cell. Furthermore, different types of battery cells are tested under the same testing conditions to evaluate their performance, or to evaluate the most suitable charging and discharging conditions and usage conditions for a particular product.
3)Capacity Test
The capacity of a battery pack is usually integrated based on two conditions: discharge current and time. Therefore, the discharge current during capacity testing will affect the final capacity measurement. Although each battery has the manufacturer's indicated specifications and is commonly tested at a low charge discharge rate, power batteries should often be charged and discharged at a state higher than the high charge discharge rate, If only referring to the specifications to set the capacity of the power battery, there will be a gap between it and the actual capacity. In actual situations, it is necessary to refer to the charging and discharging rate of the final power battery to test its battery cells, in order to obtain more accurate power battery capacity.
4)Battery pack charging/discharging characteristics test
Lithium ion batteries usually adopt a constant current to constant voltage charging mode. Starting charging is a constant current stage, and the voltage of the battery is low. During this process, the charging current remains stable and unchanged. As charging continues, the battery voltage gradually increases to 4.2V. At this point, the charger should immediately switch to constant voltage charging, with charging voltage fluctuations controlled within 1% and charging current gradually decreasing. When the current drops to a certain range, it enters the trickle charging stage. Trickle charging, also known as maintenance charging, in the maintenance charging state, the charger continues to charge the battery at a certain charging rate, and finally puts the battery in a sufficient state. There are significant differences in the variation of battery voltage under different discharge rates. The higher the discharge rate, the lower the battery voltage at the corresponding remaining capacity. Using a discharge rate of 0.2C, the rated capacity can be released when the voltage of the individual battery drops to 2.75V. When using a 1C discharge rate, it can discharge 98.4% of the rated capacity.
5)Battery pack pulse charging/discharging characteristic test
The diffusion rate of lithium ions between electrodes determines the charging rate of lithium-ion batteries. Slow diffusion of lithium ions inevitably leads to concentration polarization of lithium ions, especially during high current charging. Concentration polarization can cause the battery terminal voltage to rapidly rise to the charging termination voltage. To overcome these difficulties, pulse charging technology is applied to lithium-ion batteries. Insert idle time and discharge pulses during the charging process. Short idle time and discharge pulses can effectively eliminate concentration polarization and increase power transmission rate. Therefore, it can improve the utilization rate of active materials and accelerate the charging process.
6)Battery pack charge retention and recovery capacity test
The detection of charge retention capacity and charge recovery capacity mainly tests the capacity retention of lithium-ion batteries after being stored for a period of time, and recharges the battery after the charge retention test, following certain test steps to verify its capacity recovery.
7)Battery pack charging and discharging efficiency test
The operating cost and service life of battery modules/pack are directly related to the power performance of the battery pack. Therefore, it is necessary to fully utilize the limited energy of lithium battery packs to reduce the operating cost of the battery pack and extend the service life. Therefore, it is necessary to study the charging and discharging efficiency of the battery pack during use, establish the optimal charging and discharging performance model of the battery pack, shorten charging time, and improve the energy released by the battery pack, ensure that the energy stored in the battery pack meets the requirements of the vehicle throughout its entire service life. The charging efficiency is related to the charging system used and the depth of discharge of the battery before charging; The discharge efficiency is related to the total resistance loss and discharge current size of the system.
8)Individual temperature characteristic test
Lithium batteries have an impact on their capacity under different temperature conditions. Under the same charging and discharging conditions, the higher the temperature, the higher the capacity. Conversely, the lower the temperature, the lower the capacity.
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