Coordination of Distributed Reactive Power Sources for Voltage Support of Transmission Networks

The provision of voltage support from distribution systems to transmission networks requires new cost-effective coordination schemes to drive thousands of non-centrally monitored distributed energy resources (DERs). In this paper, we demonstrate how small-scale photovoltaic systems in distribution systems can provide reactive power services to other networks. This is achieved by means of their local controllers that change their logic to respond to external requests. These controllers operate with local information and without direct knowledge of the full system performance. This facilitates scalability as new DERs can be added to participate in a plug-and-play fashion. The paper focuses on the voltage support concept for the Swiss transmission system. The coordination defines when DERs must participate in voltage support, which task to perform and how to fulfill it. It is demonstrated that dispersed units can engage in system objectives, and still be able to support local voltages when required. The proposed approach is tested in different systems with high penetration of PV systems.