Research on SOC Estimation Based on Room-temperature SOC-OCV Curve and Capacity Normalization for Li-ion Batteries

Bingxiang Sun, Yangxi Li, Zhanguo Wang, Pengbo Ren, Wendy Jiang

Abstract


The Open Circuit Voltage (OCV) is a measure of the electromotive force of the battery, which has a monotonic relationship with the State of Charge (SOC). This relationship is widely used inSOCestimation. However, Li-ionbatteries have different capacities available at different temperatures, leading to the great variation of the SOC definition. In addition,the OCV-SOC curve of the battery varies greatly at different temperatures.And it isthusnecessary to store multiple OCV-SOC curves or OCV-Temperature fitting curves at different SOC in hardware while using this method.Thereforeit comes with great challenge to accurately estimate SOC of batteries at different temperatures.In this paper, wepropose a method to normalize battery capacity by top SOC alignment, which is adopted to estimate SOC at -20 °C~+55 °C only by the OCV-SOC curve at room temperaturefor Li-ionbatteries (LiNi1/3Co1/3Mn1/3O2, NCM). The normalized OCV-SOC curves are very similar, and the curve at room temperaturecan be used to represent the curves at other temperatures. Experimental results indicate that this proposed method exhibits a high accuracy and can reduce the data volume dramatically for SOC estimation. It delivers a good engineering solution for battery management system in electric vehicles and power grid energy storage.

Keywords


NCM Li-ion battery; SOC estimation; Capacity normalization; OCV curve


DOI
10.12783/dteees/iceee2018/27784

Refbacks

  • There are currently no refbacks.