Method for solving open circuit voltage and state of health of battery pack based on constant-current charging and discharging voltage curve

Abstract

The invention discloses a method for solving the open circuit voltage and the state of health of a battery pack based on a constant-current charging and discharging voltage curve, which comprises three stages such as open circuit voltage curve characteristic analysis under constant-current charging and discharging, battery open circuit voltage solving based on curve transformation and battery packSOH (State of Health) estimation based on OCV-SOC (Open Circuit Voltage-State of Charge) curve transformation. In the open circuit voltage curve characteristic analysis stage, a battery constant-current charging and discharging test is conducted under the multiplying power of 0.3C, and an intermediate value is solved by using an interpolation method so as to obtain an OCV-SOC curve. Compared witha curve extracted by using a standing method, there is a rising trend at the tail end of the curved extracted by using the multiplying power of 0.3C, and the characteristics of the battery are displayed more accurately. In the battery open circuit voltage solving stage, the OCV-SOC curves almost coincide with each other after being horizontally stretched by k times at different cycle times, and the battery open circuit voltage is obtained according to the unique curve. In the battery pack SOH estimation stage, the SOH of the single battery is a drawing coefficient, and the SOH of the batterypack in which multiple single batteries are connected in series is Qpack / Qinitial. According to the method, the update of the OCV-SOC curve can be quickly realized, and the SOH of the battery pack issolved by directly utilizing the OCV-SOC curve transformation.

Description

technical field [0001] The invention belongs to the technical field of electric vehicles, and in particular relates to a method for solving the open-circuit voltage and health state of a power battery pack of an electric vehicle. Background technique [0002] Accurately estimating the state of health (SOH) of the battery pack provides a reference for battery life estimation and safety assessment, which is conducive to improving the overall performance of the battery management system and ensuring the cruising range of electric vehicles. The SOH of the power battery pack is closely related to the number of battery cycles, the operating conditions of the vehicle and the battery manufacturing process. Its aging mechanism is complex, and it is difficult to estimate the SOH online. [0003] At present, the health status of the battery is mostly measured by the increase in battery internal resistance or the decrease in capacity. A typical algorithm is the dual-time scale extended ...

AI Technical Summary

Problems solved by technology

The open-circuit voltage of the battery is often obtained by the static method, that is, the hybrid pulse characteristic test (Hybrid Pulse PowerCharacteristic, HPPC) is set to obtain the OCV-SOC curve. The voltage can be considered as the open circuit voltage, which cannot meet the test conditions in practical applications

In addition, the initial calibrated OCV-SOC relationship curve is generally used as a reference standard in the application, and the curve cannot be updated with the battery life, so the estimation effect will be affected to a certain extent

[0004] For lithium iron phosphate batteries, there is a voltage plateau in the middle area of ​​the OCV-SOC relationship curve, so there are higher requirements for the method of obtaining the open circuit voltage. The researchers proposed to use the pulse or low current static method to obtain high-precision OCV-SOC relationship curve, but how to quickly obtain the OCV-SOC relationship curve and then apply it to the online SOH estimation of battery packs still needs to be further studied

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