Ancillary Frequency and Voltage Support Provision by Renewable Energy Sources in a Medium Voltage Distribution Network

The penetration of renewable energy sources (RES) is changing the characteristics of electrical distribution networks. One of the most affected aspects is the network stability. Thus, the system operators are imposing new requirements on RES to provide grid-support services. Significant part of these services focuses on the system stability improvement where RES can have large impact, thanks to their fast response time. Besides RES, such services can be provided by other converter interfaced generation (CIG) devices (e.g. batteries). Although the overall impact of such services on the network stability is positive, they can lead to system instabilities under certain conditions. In this paper, the provision of grid-support services and their overall effect on the network is studied for several distribution network scenarios An overall positive effect of such services is demonstrated, as well as the potential negative effect at high levels of RES penetration. In such case, the interaction between RES and batteries can lead the system to instabilities. The analysis conducted in this paper is focused on both network sensitivity and transient stability and it includes simulation results from models implemented in DIgSILENT-PowerFactory.