Coordinated Vertical Provision of Flexibility From Distribution Systems

The large dispersion of flexibility providing units among all voltage levels of the power system requires large, comprehensive grid models to assess the impact of flexibility usage during system operation. For this reason, aggregation methods are used to enable distributed concepts. This paper proposes a decentralized and hierarchical approach for the practical implementation of coordinated, vertical flexibility provision across multiple voltage levels, with the feasible operation region as an interface between adjacent grids. A top-down disaggregation process, based on a linear OPF model, is introduced in this paper. It is used during a flexibility provision request to distribute the requested operation point change to the underlying flexibility providing units. The objective function for this disaggregation process is chosen according to operational aspects. Both implemented methods for aggregation and disaggregation of flexibility consider grid constraints. The proposed concept is field tested during regular grid operation in a real distribution system. The results of the conducted studies show that accurate system operation in the more volatile distribution systems requires shorter time intervals compared to the transmission system. Good results with small control deviations were achieved by using time intervals of one minute for the MV and ten seconds for the LV level.