A method for estimating the unbalanced capacity of lithium iron phosphate battery system

Abstract

The invention discloses an estimation method of imbalance degree of capacity of a LiFePO4 battery system. The estimation method comprises the following steps: collecting time and current data of the maximum cell voltage Vmax and the minimum cell voltage Vmin of vehicles in the charging process; smoothing the data, performing capacity differential processing, and meanwhile, performing constructionprocessing on dQ / dV and V; classifying peaks in dQ / dV-V figures into P1-P3; calculating peak potential difference between the same peaks, and solving peak potential difference delta V of dQ / dVmax anddQ / dVmin; calculating the imbalance degree delta SOC by use of the obtained peak potential difference delta V. The imbalance of the vehicles adopting the LiFePO4 battery system can be recognized, battery systems with large imbalance degree can be judged, balance treatment is performed on the vehicles timely, the energy use efficiency of the battery systems of the vehicles can be improved, the vehicle miles of travel can be increased, SOC hopping can be reduced, and undervoltage alarm when SOCs are located in normal application intervals can be reduced.

Description

technical field [0001] The invention relates to the application field of new energy vehicle power battery technology, and more specifically to a method for estimating the unbalanced capacity of a lithium iron phosphate battery system. Background technique [0002] The power battery system of a new energy vehicle is composed of several cells connected in series and parallel. The performance of the system is affected by the consistency of the cells. Different rates, capacity decay rates, and Coulombic efficiency will lead to inconsistencies in the SOC between battery cells, that is, capacity imbalance. This unbalanced phenomenon will reduce the available capacity of the battery system, reduce the utilization efficiency, and reduce the mileage of the vehicle. [0003] In the current battery management system (BMS), the voltage difference between the highest and lowest cells in each cell is usually used to judge the unbalanced capacity. However, for the lithium iron phosphate s...

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Problems solved by technology

[0002] The power battery system of a new energy vehicle is composed of several cells connected in series and parallel. The performance of the system is affected by the consistency of the cells. Rate, capacity decay rate, Coulombic efficiency, etc. will lead to inconsistencies in the SOC between battery cells, that is, the capacity is not balanced

This unbalanced phenomenon will reduce the available capacity of the battery system, reduce the utilization efficiency, and reduce the mileage of the vehicle.

[0003] In the current battery management system (BMS), the voltage difference between the highest and lowest cells in each cell is usually used to judge the unbalanced capacity. However, for the lithium iron phosphate system, because of its flat voltage platform, the dynamic voltage The difference is mainly caused by the polarization difference between the cells, and the static pressure difference is mainly caused by the inconsistent difference in battery manufacturing, and the capacity difference cannot be accurately fed back; and the pressure difference often does not reach the alarm value after the capacity imbalance of the battery system has occurred, so There are flaws in using differential pressure for lithium iron phosphate system as a method to judge capacity imbalance

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