Loss Model for Improved Efficiency Characterization of DC Coupled PV-Battery System Converters

The use of battery energy storage systems (BESS) is emerging in residential settings, complementary to the existing presence of photovoltaic (PV) systems. BESS can play a vital role in distributed energy generation. The latest efficiency guidelines for PV-battery systems, the Effzienzleitfaden presented by the German BVES only characterize the efficiency for singular power flows, which falls short in correctly representing the operational reality of the combinatory power flows present in a DC coupled PV-battery system. A loss model is proposed. The experimental case study of a commercially available DC coupled PV-battery converter system allows to perform a least-squares fitting using experimental measurements. The proposed loss model accurately characterizes the efficiency of the converter both in modes of singular and combinatory power flows. Comparison between the proposed model and a quadratic loss model based on the datasheet has shown that the data available on a datasheet is insufficient to accurately model combinatory power flow losses.