Distributionally Robust Frequency-Constrained Microgrid Scheduling Towards Seamless Islanding

TL;DR

This paper introduces a distributionally robust microgrid scheduling model that ensures frequency security during unscheduled islanding events by co-optimizing various system controls under uncertainty.

Contribution

It develops a novel robust optimization framework using Wasserstein ambiguity sets to handle RES uncertainty and frequency constraints during islanding.

Findings

Model effectively maintains frequency security during islanding.

Proposed approach outperforms traditional methods in case studies.

Robust scheduling reduces risk of frequency instability.

Abstract

Unscheduled islanding events of microgrids result in the transition between grid-connected and islanded modes and induce a sudden and unknown power imbalance, posing a threat to frequency security. To achieve seamless islanding, we propose a distributionally robust frequency-constrained microgrid scheduling model considering unscheduled islanding events. This model co-optimizes unit commitments, power dispatch, upward/downward primary frequency response reserves, virtual inertia provisions from renewable energy sources (RESs), deloading ratios of RESs, and battery operations, while ensuring the system frequency security during unscheduled islanding. We establish an affine relationship between the actual power exchange and RES uncertainty in grid-connected mode, describe RES uncertainty with a Wasserstein-metric ambiguity set, and formulate frequency constraints under uncertain post-islanding power imbalance as distributionally robust quadratic chance constraints, which are further transformed by a tight conic relaxation. We solve the proposed mixed-integer convex program and demonstrate its effectiveness through case studies.