AC/DC Conversion Efficiency of a Sodium-Nickel based BESS: an experimental characterization

This paper concerns the experimental characterization of the AC/DC power conversion module relative to the Battery Energy Storage System (BESS) operating in the PrInCe experimental microgrid of the Polytechnic University of Bari. The goal is to characterize a polynomial model allowing for a unified formulation of BESS constraints (i.e., valid in both charge and discharge modes) in economic dispatch problems. The manuscript reports collected experimental data relative to a commercial 60 kW/180 kWh Sodium-Nickel BESS, along with a detailed description of the employed test protocols and measuring setup. With reference to the AC/DC conversion efficiency of the device under investigation, analyses carried out on the acquired samples show a slight asymmetry between charging and discharging BESS operating conditions. This behavior is properly predicted by the identified polynomial model, whose deviation with respect to experimental data always results lower than 2%.