Grid services with PV-converters in distribution systems

The most affected parts of the electrical power system in Germany are the distribution grids due to the rapid expansion of renewable energies. Most of these micro power plants e.g. photovoltaic systems feed into the low (LV) and medium (MV) voltage level. The voltage stability in these levels is thus much more complex and is partially violated in moments of strong feed-in. To reduce this negative impact the directive VDE-AR-N 4105 was specified that PV-inverters must provide reactive power instead of pure active power. This directive should however only be the beginning. In a smart grid, the asset inverter should be used much more intensively. In this paper it is demonstrated by power flow simulations with the data of a real distribution grid including PV-system feed-in that there are more possibilities but providing the reactive power for the distribution and voltage stability. It is illustrated that the use of the complete apparent power of the inverter is a more appropriate way to obtain the stationary stability of distribution grids. With this strategy in addition, the power loss can be influenced in LV- and MV-level and the power factor of the feed-in of the HV/MV-supplying transformer can be adjusted.