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Energy Storage Conversion Lab.

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Covariance controlled state-of-charge estimator of LiFePO4 cells using a simplified hysteresis model
Content type 2018
Title of paper Covariance controlled state-of-charge estimator of LiFePO4 cells using a simplified hysteresis model
Author Chang Yoon Chun, B.H.Cho, Jonghoon Kim
Publications Electrochimica Acta
Status of publication published
Vol 265
Link 관련링크 https://www.sciencedirect.com/science/article/pii/S0013468618302251 53회 연결

Equivalent circuit model (ECM)-based state-of-charge (SOC) estimation has been considered as one of

the most important aspects in battery management system (BMS). However, in case of a lithium iron

phosphate (LiFePO4) cell, because of the flatness and hysteresis effect of the open-circuit voltage (OCV)

curve, there are inevitable drawbacks directly related to both erroneous SOC information and the slow

SOC convergence speed caused by incorrect OCV characteristics. Therefore, this approach gives insight to

the design and implementation of the ECM-based SOC estimator that is suitable for an actual LiFePO4 cell.

Two approaches for settlement in current OCV issues are as follows. Firstly, through linearization between

coordinated charging and discharging OCVs, an OCV hysteresis model can be easily implemented.

This model incorporating OCV measurement data is adequately applied to the model-based SOC estimator

using the extended Kalman filter (EKF). Secondly, a well-adjusted measurement error covariance

controlled in the EKF is used to alleviate an undesired SOC fluctuation that surely results in low BMS

performance. This measurement error covariance additionally enables us to provide the fast SOC

convergence speed against an inaccurate initial SOC value. This approach has been sufficiently validated

by extensive experimental results conducted on LiFePO4 cells that had a rated capacity of 14 Ah by EIG.

Consequently, our validation showed the clearness of the proposed work for a reliable SOC estimator of a

LiFePO4 cell.