Lithium-ion battery balance management -Lithium - Ion Battery Equipment

Lithium-ion battery balance management -Lithium - Ion Battery Equipment

When it comes to battery balancing, it has basically touched the core area of ​​BMS. First of all, it is necessary to understand a few issues.

1. There is a limit to battery balancing, and the effect should be evaluated with certain parameters.

2. Battery balance In HEV and EV, the requirements are very different.

3. The effect of battery balancing must be a game and compromise with cost and additional energy consumption.

Reason for balance:
Both EVs and HEVs have to withstand large instantaneous currents during the charging and discharging phases, and they are manifested in regenerative braking current during charging. For lithium-ion batteries, such a large charging current may be that the partially full battery directly exceeds the damaged voltage range.

The discharge stage is when the motor starts up and the car accelerates, requiring a high instantaneous energy. A large discharge current may cause some batteries to be in a state of deep discharge. First, it affects the output current, and second, the battery itself will be damaged.(Lithium - Ion Battery Equipment)

Regarding the above current calculation, it has a lot to do with the whole vehicle. I believe that after finding sufficient information and calculation formulas later, the parameters of the energy management unit (EnergyStorageSystem) power unit (powerTrainSytem) and the final vehicle body environment can be established. Some calculation and evaluation formulas can make some preliminary reviews when comparing some electric vehicles currently sold.

Differences in battery cells are mainly reflected in internal resistance and capacity differences over time and temperature. Batteries with high internal resistance and low capacity will have larger voltage swings when the discharge current is large. Batteries that differ greatly from standard batteries are more likely to be damaged, so to some extent, a balanced algorithm should be used to make the entire battery pack get rid of the short-board effect.

Equalization method classification: charge equalization, discharge equalization and dynamic equalization.

1. Charge equalization In the late stage of the charging process, the capacity of some batteries is very high, and when the cell voltage has exceeded the set limit (generally smaller than the cut-off voltage), the BMS controls the equalization circuit to start to work, and controls the capacity to be full. The battery is less charged, not charged or even transferred energy, in order to achieve the purpose of continuing to charge the battery with a small capacity in the entire battery pack and the battery with full capacity will not be damaged.

The function of charge equalization is to prevent the batteries in the battery pack from being overcharged, and some structures may have some negative effects during discharge use. Since the charge equalization only ensures that the battery is being charged, the battery with the smallest capacity is not charged, and during the discharging process, the energy it can release is also the smallest, so these batteries have a high possibility of being over-discharged. If the BMS is not well controlled, these small-capacity batteries are already in a deep discharge condition, and the battery pack as a whole still contains higher energy (in the form of a higher battery pack voltage). Often charge equalization is used in conjunction with discharge equalization.



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