Dynamic system performance of renewable power generation units — Useful and doubtful grid code requirements

To maintain system stability and functioning and to ensure the quality of supply, system operators are responsible to set up transparent and commonly valid requirements for the usage and connection to their relevant grids. Facing the increasingly high penetration of dispersed power generators the requirements have been continuously updated and revised by TSOs and DSOs according to the new challenges of its transforming traditional operation procedures in all European Member States over the last decade. Based on gathered experiences in many years the reasonable needs for specifically designed and more stringent requirements with respect to system management and control schemes of renewable energy systems (RES) have evolved. However the accurate definition of advanced requirements is still ongoing and manufacturers are subjected to a rather dynamic technical as well as legislative framework in this context. In fact, ENTSO-E is currently working on a first pan-European grid code. In some ways also DSOs are overcharged in choosing the most suitable solution with respect to their alternatives like reactive power contribution of RES. Hence the intention of this paper is to highlight the contemporary sophisticated requirements related to the dynamic performance of RES during system disturbances and their respective contribution to system recovery and voltage support. The investigation of the required capabilities shows for example that under specific system conditions and operation modes the intended support function of injecting reactive current during voltage dips may not lead to the anticipated but rather to unsolicited impacts on the system that even can contradict the intention of system recovery. The corresponding analysis is based on simulations performed in German wind farm certification procedures by using manufactu