Power Utility Tests for Multi-MW High Energy Batteries

Abstract

This paper reviews the procedures, layouts and metrics described in the new test manual issued by the Electric Power Research Institute (EPRI), in order to determine the performance, functionality and equivalent models of a utility scale battery energy storage system (BESS). In this approach, the large battery unit is connected to the dc-link of a bidirectional power conversion system (PCS), which may be interfaced with either the utility grid or a load bank for the purpose of estimating the BESS operation and performance characteristics, some of which includes; available charge/discharge energy at rated power, continuous charge/discharge duration, battery ramp rate, and ac round trip efficiency (RTE). For the purpose of characterizing and verifying the functionalities of the utility sized BESS, the bidirectional converter is operated with different charge and discharge cycles relevant to each specification and the battery state of charge along with electrical measurements at the ac and dc side are monitored and recorded. Also, an electrical equivalent circuit for a utility scale battery unit was developed based on the 1MW/2MWh operational BESS at the LG&E and KU E.W. Brown facility. This model was formulated using an improved method for estimating the battery cell parameters.

Parameter Identification for Cells, Modules, Racks, and Battery for Utility-Scale Energy Storage Systems

“…In order to meet the ratings of the power conditioning device, the experimental battery system includes 20 racks, which are equally distributed between two identical containers. A rack includes 17 LG Chem M48126P3B1 battery modules, each with 14 Li-ion cells and rated for 126Ah at 51.8V nominal voltage. This battery system also employs a BMS, whose function includes the supervision of cell performance and balancing the SOC across all cells.…”

“…lent circuit parameters of a utility-scale battery system and its sub-components using equipment typically available at installation sites. An approach describing how the equivalent circuit parameters of a cell compares to that of a battery system with identical cells connected in series and parallel was proposed by the authors in [17]. This work emphasizes how the difference in parameters of cells within a battery system can lead to significant variations in terminal voltages and defines a metric for comparing the voltage performance of utility-scale battery models developed using select cell, module, or rack parameters.…”