Flexibility Procurement for Local Ancillary Services and Provider Aggregation Perimeter in Radial Distribution Systems

User-side flexibility can significantly contribute to the management of distribution systems. The flexibility useful to Distribution System Operators (DSOs) is strongly local; at the same time, it should be engaged through market mechanisms. The concept of flexibility perimeter is useful for meeting both DSO’s and market needs; it is based on the approach of Load Area (LA), a set of buses where the power injection has a comparable impact on grid operation. In a radial grid, the perimeter of flexibility providers for congestion relief services is easily identifiable; this is not the case for voltage support services. A large perimeter might be beneficial from a market perspective, but might only allow limited participation in service provision due to grid constraints. To assess the influence of grid partition in LAs on market results for voltage support services, in the paper the problem of optimal flexibility procurement with a market approach is presented, with the DSO’s needs for secure network operation and detailed representation of the flexibility providers’ offers and capabilities. The optimal procurement model is applied to three case studies, each with different grid partitions and flexibility offers; the results show the influence of grid partition on market outcomes for flexibility-based voltage support services.