Power Utility Tests for Multi-MW High Energy Batteries

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 and functionality 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). 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.