  Online decision support for effective mitigation actions against propagating
cascading outages in a power grid still poses a big challenge to grid
operators. This paper proposes an online mitigation strategy against cascading
outages using an optimal power flow model based on a Dynamic Interaction Graph.
For a given power grid, its interaction graph, also called an interaction
model, was proposed in recent literature, which is composed of components and
links that have large contributions to outage propagation. Differing from a
conventional interaction graph, a Dynamic Interaction Graph can adaptively
update its parameters with changes of grid topology and hence is more accurate
in online identification of the most vulnerable transmission lines and likely
outage propagation paths for mitigation. Further, the paper introduces an
optimal power flow model based on the proposed Dynamic Interaction Graph for
determining the optimal control strategy to maintain transfer margins of
vulnerable transmission lines and effectively mitigate outage propagation. The
numerical results on the IEEE 118-bus system demonstrate the effectiveness of
the proposed models and associated control strategy.
