Robust VAR Capability Curve of DER with Uncertain Renewable Generation

TL;DR

This paper develops a robust VAR capability curve for distribution systems with high renewable uncertainty, enabling TSOs to better utilize DER flexibility for reactive power support.

Contribution

It introduces a method to incorporate renewable generation uncertainty into the aggregation process, preserving system physics and providing probabilistic capability curves.

Findings

The proposed method quantifies renewable uncertainty effectively.

The capability curve includes probability measures for better decision-making.

It enhances the reliability of DER-based VAR support in uncertain conditions.

Abstract

Active distribution system with high penetration of inverter based distributed energy resources (DER) can be utilized for VAR-related ancillary services. To utilize the DER flexibility, transmission system operator (TSO) must be presented with the aggregated DER flexibility of distribution system. However, the uncertainty in renewable generation questions the credibility of aggregated capability curve in practice. In this paper, we incorporate the uncertainty into aggregation process to develop a robust capability curve while preserving the real physics (unbalance and lossy nature) of distribution system. Statistical inference method is employed to quantify uncertainty in solar generation and quantified uncertainty is integrated into a chance constrained optimal power flow (OPF). It provides the grid operator with the dispatchable aggregated reactive power capability. The resulting capability curve with the associated probability can be harnessed by the TSO for decision making for both planning and operation.