DC current injection into the network from PV inverters of <5 kW for low-voltage small grid-connected PV systems

The present paper is focused on the study of DC current injection for low-voltage small grid-connected PV systems, which is one of the power quality requirements of utility companies. To achieve this aim, the existing status of guidelines and regulations in six selected countries where the development in the grid PV sector has evolved rapidly over the last decade (Australia, Germany, Japan, Spain, the United Kingdom and the United States) has been reviewed according to the DC current injection into the grid. Furthermore, a grid-connected system installed in Spain has been used to carry out measures concerning possible DC current injection into the grid. Thus, 12 single-phase inverters <5 kW (according to the transformer options: 50 Hz LF transformers, HF transformers or transformerless) from the European market have been tested. Many groups of measurements were made under different conditions. The results show that in all cases there is DC current injection, even if an LF transformer inverter is used.