Harnessing Flexibility of Distribution System With Uncertain Loads and DERs

The aggregated capability distributed energy resources (DER) and controllable loads present in active distribution systems (D-system) can be an additional source to support need of future grid which can be economical and emission free. To engage these DERs & make use of the D-system's flexibility in the transmission side, distribution system operators (DSOs)/aggregators need to aggregate individual DERs' capability and communicate it to the transmission system operators (TSOs). However, the variability in DERs and loads makes the aggregated capability region contentious. The objective of the paper is to construct a probabilistic active and reactive power (P-Q) flexibility region of the distribution system which can be leveraged to support the transmission grid during contingencies. In this work, uncertainty is incorporated into the aggregation process by formulating a chance-constrained OPF. The resulting P-Q flexibility region with the associated probability can be used by the aggregator to determine the level of participation in the energy market and ancillary service commitments. The P Qflexibility region is expected to be valid in real-world scenarios as it takes different practicalities into account such as device state and the unbalanced nature of the distribution system.