Identifying Secure Operating Ranges for DER Control using Bilevel Optimization

TL;DR

This paper presents a bilevel optimization framework to identify secure operating ranges for distributed energy resources in unbalanced distribution grids, enabling third-party control without violating grid constraints.

Contribution

It introduces a novel bilevel optimization approach that determines aggregate DER flexibility while ensuring no disaggregation leads to grid violations, simplifying control rules.

Findings

Wide range of DER flexibility identified

Control rules prevent grid constraint violations

Framework validated on two distribution feeders

Abstract

Active distribution grids are accommodating an increasing number of controllable electric loads and distributed energy resources (DERs). A majority of these DERs are managed by entities other than the distribution utility, such as individual customers or third-party aggregators, who control the loads and DERs without consideration of any distribution grid constraints. This makes it challenging for a distribution system operator (DSO) to allow third-party aggregators and transmission operators to fully exploit the flexibility offered by these resources while also ensuring that distribution grid constraints such as voltage magnitude limits are not violated. In this paper, we develop a bilevel optimization-based framework to determine the aggregate power flexibility that can be obtained from an unbalanced distribution grid while ensuring that there is no disaggregation solution that leads to grid constraint violations. The results are a set of constraints and operating rules that are easy to communicate, and which provide the entities that procure flexibility from DERs (e.g. transmission operators or third-party aggregators) with the ability to freely implement their own disaggregation strategy without intervention from the DSO. The proposed approach is tested on two unbalanced distribution feeders and our simulation results indicate that it is possible to determine a wide range of aggregate power flexibility, as long as a simple set of rules for DER control activation are followed.