Measurement and Estimation of the Equivalent Circuit Parameters for Multi-MW Battery Systems

This paper proposes and validates through simulations and measurements, a procedure for the determining the equivalent circuit parameters of large utility-scale batteries. It is considered that a large battery includes multiple cells connected in series and parallel, and therefore, its equivalent circuit can be represented as a series-parallel network of state of charge (SOC) dependent resistors and capacitors. Tests for determining these equivalent circuit parameters are proposed. These tests involve subjecting the battery energy storage system (BESS) to multiple charge and discharge cycles, while monitoring the terminal voltage and current response. A method for post-processing and analyzing the measurements in order to obtain an equivalent circuit model that accounts for the dynamic properties of the battery system and differences between the parameters of each cell is developed. The measurements and simulations are conducted for a 1MW/2MWh BESS demonstrator located at the Louisville Gas and Electric and Kentucky Utilities (LG&E and KU) E.W. Brown generating plant.