  Incorporating the AC power flow equations into unit commitment models has the
potential to avoid costly corrective actions required by less accurate power
flow approximations. However, research on unit commitment with AC power flow
constraints has been limited to a few relatively small test networks. This work
investigates large-scale AC unit commitment problems for the day-ahead market
and develops decomposition algorithms capable of obtaining high-quality
solutions at industry-relevant scales. The results illustrate that a simple
algorithm that only seeks to satisfy unit commitment, reserve, and AC power
balance constraints can obtain surprisingly high-quality solutions to this AC
unit commitment problem. However, a naive strategy that prioritizes reserve
feasibility leads to AC infeasibility, motivating the need to design heuristics
that can effectively balance reserve and AC feasibility. Finally, this work
explores a parallel decomposition strategy that allows the proposed algorithm
to obtain feasible solutions on large cases within the two hour time limit
required by typical day-ahead market operations.
