Network-Cognizant Time-Coupled Aggregate Flexibility of Distribution Systems Under Uncertainties

TL;DR

This paper introduces a novel, less conservative method to efficiently approximate the feasible power injection trajectories of distributed energy resources in distribution systems, accounting for uncertainties and enhancing flexibility utilization.

Contribution

It develops an ellipsoidal inner approximation approach for the flexibility region, incorporating adaptive robust optimization to better characterize feasible trajectories under uncertainty.

Findings

Less conservative flexibility region approximation

Effective characterization of DER flexibility under uncertainty

Validated on a realistic distribution feeder

Abstract

Increasing integration of distributed energy resources (DERs) within distribution feeders provides unprecedented flexibility at the distribution-transmission interconnection. To exploit this flexibility and to use the capacity potential of aggregate DERs, feasible substation power injection trajectories need to be efficiently characterized. This paper provides an ellipsoidal inner approximation of the set of feasible power injection trajectories at the substation such that for any point in the set, there exists a feasible disaggregation strategy of DERs for any load uncertainty realization. The problem is formulated as one of finding the robust maximum volume ellipsoid inside the flexibility region under uncertainty. Though the problem is NP-hard even in the deterministic case, this paper derives novel approximations of the resulting adaptive robust optimization problem based on optimal second-stage policies. The proposed approach yields less conservative flexibility characterization than existing flexibility region approximation formulations. The efficacy of the proposed method is demonstrated on a realistic distribution feeder.