Grid Voltage Influences of Reactive Power Flows of Photovoltaic Inverters with a Power Factor Specification of One

The quantity of installed photovoltaic (PV) systems in the German distribution grid is still increasing. In some areas the installed PV capacity exceeds 5.0 kWp [1] per house connection (HC). Therefore the load flow changes its characteristics and leads to new requirements for grid dimensioning. Additionally, the feed-in is carried out via inverter systems and a lot of power electronics have to be integrated in the existing grid infrastructure. This leads to new challenges to ensure the required grid stability. Due to the rapid extension of PV systems, primarily in low and medium voltage grids, the state of the grid is increasingly unknown. This article discusses unintended reactive power flows of PV inverter systems. The focus hereby is on the power factor (PF) specification of one. Hence, these PV inverters should feed-in no reactive but only active power. Various observations in low voltage grids show a dispersion of the active and apparent power feed-in and thus a reactive power flow. To investigate these unintended reactive power flows numerous commercially available inverters in the single and double digit kW range are analyzed. The investigations are based on the analysis of data from a very detailed measurement campaign in a distribution grid with high PV penetration in southern Germany. Every single inverter with a power factor specification of one shows reactive power flows. Finally it is shown, that there is an influence of the unintended reactive power flows on the grid voltage. This influence has to be considered in grid planning and power system