A method for estimating lithium battery SOC by ampere-hour integration

Abstract

The invention discloses a method for estimating the SOC of a lithium battery by an ampere-hour integral. S1, turn on the battery management system BMS, and judge whether the lithium battery is in the charging state or the discharging state according to the connection state of the charging gun charging the battery; S2, enter the charging state , the state of charge at the end of the last discharge state is obtained as the state of charge (SOC) at the initial moment of this charge 0 ) N ; S3, judging whether the lithium battery reaches a fully charged state every time T during charging, if so, enter step S4, otherwise enter step S3; S4, use the ampere-hour integral to calculate the state of charge (SOC) of the lithium battery N and state of charge SOC error (ΔSOC) N ; S5, calculate discharge factor F N , storage discharge factor F N and (SOC 1 ) N ; S6, obtain the state of charge at the initial moment of the discharge state as (SOC 0 ) N+1 ; S7, utilizing the ampere-hour integral to calculate the state of charge (SOC) of the lithium battery during discharge 1 ) N+1 . The introduction of the discharge factor in the invention can not only calibrate the error caused by the current sensor, but also calibrate the capacity error caused by battery aging.

Description

technical field [0001] The invention relates to the field of battery management systems, in particular to a method for estimating the SOC of a lithium battery by ampere-hour integration. Background technique [0002] As one of the core components of electric vehicles, the battery management system (Battery Management System, BMS) has always been the focus of electric vehicle research and development. The core function of BMS is to maintain and manage the power battery of electric vehicles, ensure the safe and efficient operation of batteries, and improve the driving range and driving experience of electric vehicles. To realize these functions, it is first necessary to make an accurate estimation of the operating state of the battery, especially the State of Charge (SOC). [0003] At present, the combination of the ampere-hour integration method and the open circuit voltage method is commonly used in BMS to estimate the SOC of lithium batteries. The ampere-hour integration ...

AI Technical Summary

Problems solved by technology

However, there are three defects in the ampere-hour integration method: first, the ampere-hour integration method depends on the initial value of SOC. When there is an error in the initial SOC, the estimated SOC will always have an error; second, the ampere-hour integration method depends on the sensor accuracy. And sampling frequency, improving sensor accuracy will bring about a rapid increase in hardware costs; third, the ampere-hour integration method depends on battery capacity, battery capacity will change with temperature and battery attenuation, and inaccurate battery capacity will also bring SOC error

This method also has the following defects: first, the battery needs to be left standing for a long time, which does not meet the real-time requirements; second, the accuracy of the SOC-OCV curve is high, if the curve obtained in advance is not accurate, the open circuit voltage method The effect may be counterproductive; third, for lithium iron phosphate batteries, there is a voltage plateau period (SOC is in the range of 20% to 90%, and the change range of OCV is small), and the sensor measurement error will bring a large SOC error

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