  Transmission line failures in power systems propagate and cascade
non-locally. In this work, we propose an adaptive control strategy that offers
strong guarantees in both the mitigation and localization of line failures.
Specifically, we leverage the properties of network bridge-block decomposition
and a frequency regulation method called the unified control. If the balancing
areas over which the unified control operates coincide with the bridge-blocks
of the network, the proposed strategy drives the post-contingency system to a
steady state where the impact of initial line outages is localized within the
areas where they occurred whenever possible, stopping the cascading process.
When the initial line outages cannot be localized, the proposed control
strategy provides a configurable design that progressively involves and
coordinates more balancing areas. We compare the proposed control strategy with
the classical Automatic Generation Control (AGC) on the IEEE 118-bus and
2736-bus test networks. Simulation results show that our strategy greatly
improves overall reliability in terms of the N-k security standard, and
localizes the impact of initial failures in the majority of the simulated
contingencies. Moreover, the proposed framework incurs significantly less load
loss, if any, compared to AGC, in all our case studies.
