Brief description of lithium ion battery management system

　　Mainly briefly describe the lithium-ion battery management system, so that everyone can further understand the relevant knowledge of lithium-ion batteries.

　　1.1 Naming Rules

　　Single cell (CELL): The most basic element of a battery, a single cell, providing 3V-4V.

　　Battery block (BLOCK): Single cells are connected in parallel, providing a voltage of 3V-4V.

　　BATTARY: An independent physical module composed of a series of single cells or battery blocks in series, which can provide a higher voltage.

　　Battery pack (pack): A battery assembly composed of many batteries connected in series or in parallel.

　　1.2 Safe operation area

　　The safe operating area of lithium-ion batteries is determined by current, temperature, and voltage.

　　●If the voltage threshold is overcharged, the battery will be destroyed quickly, and it will explode in severe cases.

　　●Most lithium-ion battery cells will be destroyed if they continue to discharge when the voltage is below the threshold.

　　●If the lithium ion battery is discharged outside a certain temperature range, or charged in a relatively smaller temperature range, the life of the lithium ion battery will be seriously damaged.

　　●Lithium-ion single batteries that have been working outside the allowable temperature range for a long time are prone to thermal runaway and spontaneous combustion imagination. Even the single battery that is not prone to thermal runaway, the organic electrolyte contained in it will help combustion.

　　●Lithium-ion single cells will be damaged if they work for a few seconds under high pulse current.

　　1.3 Energy　　Output power: P=2.3Ax3.3V=7.59w

　　Power loss: P=2.3Ax2.3Ax0.01R=0.053w

　　Conversion rate: (7.59-0.053)/7.59=99.3%

　　Charging power: P=2.3x (3.3+0.01x2.3)=7.6429w

　　Two-way charging power: (7.59-0.053)/7.6429=98.6%

　　As the current increases, the energy efficiency will decrease accordingly. More energy will be wasted in the single battery in the form of heat energy, and the energy of the single battery will be reduced accordingly.

　　1.4 Charge

　　Although the amount of charge in the charge and discharge is equal, the energy released by the discharge is less than the energy stored by the charge.

　　1.5 calendar life

　　The chemical reaction that occurs inside the standard lithium-ion single battery when the voltage is higher than 4.0V in the fully charged state.

　　1.6 cycle life

　　The capacity of a single battery shows a linear decay trend with the increase of the number of charge and discharge cycles, and the rate is related to the size of the discharge current of the single battery.

　　Part of the capacity loss is attributed to the loss of active material inside the single battery, and the other part of the capacity is not lost, but not used; the insufficient charge and discharge of the single battery is determined by the increase in internal resistance and the fixed cut-off voltage set by the manufacturer .

　　1.7 Modeling

　　Dynamic internal resistance is defined as the ratio of voltage change to current change

　　R=dV/dI

　　SOC: The internal resistance is larger when the SOC is higher and lower.

　　Temperature: The internal resistance is larger when the temperature is lower.

　　Current: The internal resistance is larger when a larger current is discharged.

　　Use: The internal resistance increases as the number of uses increases.

　　1.8 Voltage equalization problem of series string

　　2.1 Lithium-ion battery management system The role of the battery management system is to ensure that the internal single cells of the managed battery work within their own safe working area.

　　●Compared with other chemical batteries, lithium-ion batteries cannot tolerate battery abuse.　　● Large-scale battery packs composed of a large number of single cells in series are more prone to overcharge and overdischarge due to the unbalanced voltage of the internal single cells. Overcharge and overdischarge of lithium ion battery are never allowed.　　 definition:

　　●Battery monitoring

　　●Battery protection

　　●Battery state estimation

　　●Maximize battery performance

　　●User or external device feedback

　　Function:

　　●Prevent any lithium-ion battery voltage from exceeding the limit by actively stopping the charging current or feeding back the stop charging information.

　　●Prevent any lithium-ion battery temperature from exceeding the limit by directly stopping the battery current, feeding back the stop operation information or starting the cooling device.

　　●Prevent the lithium-ion battery voltage from being too low by stopping the charging current or feeding back the stop operation information.

　　●Prevent the battery charging current from exceeding the limit by feeding back the current reduction or cutting off information or directly cutting off the current.

　　●Prevent the battery discharge current from exceeding the limit.