  This paper proposes a service restoration model for unbalanced distribution
systems and inverter-dominated microgrids (MGs), in which frequency dynamics
constraints are developed to optimize the load pick-up during restoration
process and guarantee frequency stability. After extreme events, the damaged
distribution systems can be sectionalized into several isolated MGs to restore
critical loads and tripped distributed generations (DGs) by black-start DGs.
However, the high penetration of inverter-based DGs reduce the system inertia,
which results in low-inertia issues and large frequency fluctuation during the
restoration. To address this challenge, we formulate a sequential service
restoration model as a mixed integer linear programming (MILP) problem. The
proposed MILP model explicitly incorporates the frequency response into
constraints, by interfacing with transient simulations of inverter-dominated
MGs. Numerical results on a modified IEEE 123-bus system have validated that
the frequency dynamic performance of the proposed service restoration model are
indeed improved.
