  This paper provides an enhanced modeling of the contingency response that
collectively reflects high-fidelity physical and operational characteristics of
power grids. Integrating active and reactive power contingency responses into
the security-constrained optimal power flow (SCOPF) problem is challenging, due
to the nonsmoothness and nonconvexity of feasible sets in consequence of
piece-wise curves representing generator characteristics. We introduce a
continuously-differentiable model using functions that closely resemble PV/PQ
switching and the generator contingency response. These models enforce physical
and operational limits by optimally allocating active power imbalances among
available generators and deciding the bus type to switch from the PV type to
the PQ type. The efficacy of this method is numerically validated on the IEEE
30-bus, 300-bus, and 118-bus systems with 12, 10, and 100 contingencies,
respectively.
