A Fast Method To Approximate The Flexibility Region of An Active Distribution Network In Pq Space

The increase of controllable devices in distribution networks has turned distribution feeders into Active Distribution Networks (ADN), thus creating possibilities for providing flexibility that can be used by the Transmission System Operator (TSO). In particular, modern ADNs can modify their active and reactive power exchange with the transmission system through control of their own resources. This paper proposes a fast optimization-based method to approximate the ADN flexibility region at the connection point with the transmission system in the PQ space. The method identifies boundary points of the ADN flexibility region by solving a modified second-order cone optimal power flow problem. Using the boundary points, a polygon approximation of the flexibility region is formed and expressed as linear inequality constraints that can be used to solve a centralized optimization problem which provides reference PQ values for each ADN. The proposed approach is implemented on two test feeders and is evaluated for its precision and computation time.