The transition to sustainable power systems with a high penetration of renewable energy sources and distributed generation is one of the major challenges of the future energy supply. So far mainly conventional power plants provide ancillary services such as frequency and reactive power control. With the increasing penetration of distributed generation systems this has to change. In this paper, it is assumed that all generation units in the power system participate on the primary frequency control with a certain percentage of their current generation. For this case, this investigation presents possible approaches to participate wind-turbines and photovoltaic plants on primary frequency control and shows the results of the transient behavior by this control for several scenarios.