  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.
