Evaluation and Characterization of Direct Current Emissions caused by Inverters in the Distribution Grids

The expansion of distributed renewable energy technologies like photovoltaic systems and electric vehicle (EV) charging stations and its active power electronics causes direct current (DC) emissions in the electrical AC distribution grids which are currently not monitored. Although emissions in the harmonic frequency range (50 Hz to 2 kHz) are well standardized, for DC emissions no standards are defined yet. However, failure to detect and standardize DC emissions do have a significant negative impact on the public grid through grid disturbances or quality losses. Measurement and protection systems are affected as well as thermal effects on cables or transformers are given. In this study the DC current emissions of EV charging stations and PV systems are analyzed and characterized at the reconstructed electrical distribution grid of the university of applied sciences Technikum Vienna. The results show that the DC current emissions depend on the design of the active power used in V2G chargers and photovoltaic systems and how they vary at different power levels (low power vs. high power). The research indicates that the emissions can reach up to 200 mA from a single EV charger.