Method for computing RAC of lithium ion battery packs

Abstract

The invention discloses a method for computing the RAC of lithium ion battery packs. The method comprises the steps of firstly computing the charging load state SOC of each single lithium ion battery in each lithium ion battery pack, computing the RAC of each single lithium ion battery, thereby computing the RAC of the lithium ion battery packs, comparing the RAC of the lithium ion battery packs through a lithium ion BMS, defining the maximum value of the RAC of the lithium ion battery packs as the RAC of the lithium ion battery packs, carrying out self-learning and temperature compensation on the current internal resistance R of each single lithium ion battery in each lithium ion battery pack, diagnosing the health condition of the lithium ion battery packs, ensuring that the RAC of the lithium ion battery packs is accurately computed, and releasing the RAC in a maximized mode. Meanwhile, when the working condition changes, the lithium ion BMS still can accurately compute the RAC of the lithium ion battery packs, and provide timely maintenance information.

Description

【Technical field】 [0001] The invention relates to a method for calculating the remaining available capacity RAC of a lithium ion battery pack. 【Background technique】 [0002] At present, the calculation method of the remaining available capacity RAC of lithium-ion or lithium polymer battery packs is generally by measuring the total current of the charging and discharging circuit, and then obtaining the absolute capacity value by current integration, and then dividing it by the current actual capacity after one charge and discharge learning , to obtain the current state of charge load SOC of the lithium-ion battery pack. The limitations of this method of calculating the remaining available capacity RAC include: First, the way of current integration will produce cumulative errors and will increase with time. Second, only the current charging load state SOC of the lithium-ion battery pack can be obtained, and the remaining available capacity RAC of each single-cell lithium-ion ...

AI Technical Summary

Problems solved by technology

[0002] At present, the calculation method of the remaining available capacity RAC of lithium-ion or lithium polymer battery packs is generally by measuring the total current of the charging and discharging circuit, and then obtaining the absolute capacity value by current integration, and then dividing it by the current actual capacity after one charge and discharge learning , to obtain the current state of charge load SOC of the lithium-ion battery pack. The limitations of this method of calculating the remaining available capacity RAC include: First, the way of current integration will produce cumulative errors and will increase with time. Second, only the current charging load state SOC of the lithium-ion battery pack can be obtained, and the remaining available capacity RAC of each single-cell lithium-ion battery in series cannot be calculated, so that the remaining available capacity RAC of the lithium-ion battery pack is consistent It is impossible to make a good evaluation, and at the same time, it is impossible to control the balance according to the remaining available capacity RAC of each lithium-ion battery in real time, resulting in too low balance efficiency; third, the current charging load state SOC cannot represent the lithium-ion battery pack. The actual power that can be released under the current environment and working conditions, that is, the current charging load state SOC is not equal to the remaining available capacity RAC, and the ambient temperature, aging degree, connection status and current discharge current of the lithium-ion battery pack They are all variable, and the calculation method of using the current charging load state SOC as the current capacity reference value of the lithium-ion battery pack has serious limitations, and it is impossible for users to obtain the current real situation and comprehensive information of the lithium-ion battery pack; Fourth, in the diagnosis of single-cell failure, only the terminal voltage of a single-cell lithium-ion battery is used as the basis for judgment, and it is impossible to effectively distinguish whether the failure of a single-cell lithium-ion battery is due to increased internal resistance or capacity decay At the same time, it is impossible to locate the failed batteries; fifth, during production, it is necessary to calibrate the current sensor and perform a capacity self-learning action on a full and full discharge of the lithium-ion battery pack, which increases time and cost.

[0003] Moreover, the calculation of the remaining available capacity RAC of the lithium-ion battery pack and the charging and discharging control of the lithium-ion battery pack use different evaluation units. The former is the ampere-hour unit obtained after integrating the coulomb counter, and the latter is the measurement of a single cell connected in series. The terminal voltage value obtained after the lithium-ion battery, when the lithium-ion battery with the lowest voltage in the lithium-ion battery pack reaches the discharge cut-off voltage, the lithium-ion battery pack must stop discharging. That is, it is determined by the lithium-ion battery with the lowest voltage. When the capacity and internal resistance of the lithium-ion battery pack are inconsistent, the remaining available capacity RAC of the lithium-ion battery pack will become smaller with the expansion of this inconsistency; at the same time Since the environment and working conditions of the lithium-ion battery pack will also lead to inconsistencies in capacity and internal resistance, when the environment and working conditions change, the amount of electricity that the lithium-ion battery pack can discharge after each full charge will also change. There is a big difference, so there will be problems with inaccurate calculation of the remaining available capacity RAC of the lithium-ion battery pack. For example, when the current charging load state SOC is still 20%, it has entered the undervoltage protection; or the current charging load state SOC It is already 0, but the lithium-ion battery pack can still be discharged

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