A Novel State of Charge Dependent Equivalent Circuit Model Parameter Offline Estimation for Lithium-ion Batteries in Grid Energy Storage Applications

This paper develops a novel methodology to estimate the parameters of the Equivalent Circuit Model (ECM) for Lithium-ion battery cells focusing on their use in grid applications. The methodology considers both static and dynamic test profiles based on grid energy storage applications for identifying the battery model parameters. Parameters dependency on SOC and temperature is also included in the proposed methodology. The correlation between the parameters and the SOC is obtained through polynomial regression, in which the quality of the fitness indicates the appropriateness of the resulting trend curve. The proposed methodology is compared with two conventional methods, to validate its effectiveness and accuracy on battery parameter estimation. The proposed SOC-dependent model has shown to reduce the root-mean-square error of the estimated terminal voltage by approximately 50% when compared to that of the SOC-independent model, making it a more suitable solution for SOC and SOH estimations for grid applications.