Brief description of lithium ion battery management system

1.1 Naming rules

Single battery (CELL): The most basic constituent element of the battery, single core, providing 3V-4V.

Battery Block (BLOCK): Single battery in parallel, providing 3V-4V voltage.

Battery (BATTARY): An independent physical module consisting of a series of individual batteries or battery blocks in series, which can provide a higher voltage.

Pack: A collection of cells composed of many cells in series or in parallel.

1.2 Safe operating area

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

If the voltage threshold is exceeded, the battery will be quickly damaged and will explode in serious cases.

Most lithium-ion monomer batteries will be damaged if they continue to discharge below the voltage threshold.

If the lithium-ion monomer battery is discharged outside a specific temperature range, or charged in a relatively small temperature range, the life of the lithium-ion monomer battery will be seriously damaged.

Lithium-ion monomer batteries that have long worked outside the allowed temperature range are prone to thermal runaway and spontaneous combustion imagination. Even monomer batteries that are not easy to produce thermal runaway phenomena contain organic electrolytes that contribute to combustion.

The lithium-ion monomer battery will work for seconds under high pulse currents and will be damaged.

1.3 Energy

Output power: P = 2.3 Ax3 .3 V = 7.59 W

Power loss: P = 2.3 Ax 2.3 Ax 0.01 R = 0.053 W

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

Charge power: P = 2.3 X(3.3 + 0.01 X 2.3) = 7.629 W

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

When the current increases, the energy efficiency will be reduced accordingly. More energy will be wasted inside the monomer battery in the form of heat energy, and the monomer battery energy will be reduced accordingly.

1.4 Charge

Although the amount of charge and discharge is equal, the discharge releases less energy than the charge storage energy.

1.5 Calendar life

The internal chemical reaction of a standard lithium-ion monomer battery when the full state voltage is higher than 4.0 V.

1.6 Cycle life

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

Part of the capacity loss is due to the loss of active substances inside the monomer battery. The other part of the capacity is not lost but is not lost; The insufficient charge and discharge of monomer batteries is determined by the increase of internal resistance and the fixed cut-off voltage set by the manufacturer.

1.7 Modelling

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

R = dV/dI

SOC: Internal resistance is higher at both the higher and lower SoC levels.

Temperature: Internal resistance is larger at lower temperatures.

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

Usage: Internal resistance increases as the number of uses increases.

1.8 The problem of homogenization of series

2.1 Lithium-ion battery management system

The function of the battery management system is to ensure that the individual batteries inside the managed battery are operating within their own safe working area.

Lithium-ion batteries are more tolerant of battery abuse than other chemical batteries.

Large scale batteries composed of large numbers of monomer cells in series are more likely to overcharge and overcharge due to uneven internal monomer cell voltage. Lithium-ion monomer batteries must not be overcharged and overcharged.

Definition:

Battery monitoring

Battery protection

Battery Status Estimation

Maximize battery performance

Feedback from users or external devices

Function:

The voltage limit of any lithium ion monomer battery is prevented by actively stopping charging current or feedback stopping charging information.

To prevent any lithium ion monomer battery from exceeding the temperature limit by directly stopping the battery current, feedback to stop the operation information, or starting the cooling device.

To prevent the lithium ion monomer battery voltage from being too low by stopping charging current or feedback to stop running information.

By reducing current or cutting off current information through feedback, or directly cutting off current, the battery's charging current is prevented from exceeding the limit.

To prevent battery discharge over current limit.

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