Abstract: The data of charge and discharge current and voltage of 18650 and 26650 lithium iron phosphate batteries show that the voltage remains unchanged during the cycle aging of the battery, although the SOC value at the maximum curvature (inflection point) of the capacity voltage curve. Therefore, in the process of estimating SOC, when the discharge voltage reaches the inflection point voltage, modifying the SOC to the corresponding inflection point SOC can optimize the estimation of the ampere-hour integration method because of the initial SOC to a certain extent. Based on this, a new inflection point correction chronograph integration algorithm is proposed. The effects of temperature, charge and discharge ratio, cycle aging and other factors on the accuracy of SOC estimation are considered. The concept of inflection point of charge and discharge curve is introduced to establish a mathematical model for real-time estimation of SOC. To reduce the cumulative error problem of the ampere-time integral method. Compared with the traditional An-time integral method, the error is 3%, which indicates that the method is feasible in actual conditions, and the estimation accuracy is high, which can provide an important reference for real-time estimation and detection of SOC.

Key words: state of charge SOC, inflection point correction ampere-time integral method, real-time estimation