  Phasor measurement units (PMUs) can be effectively utilized for the
monitoring and control of the power grid. As the cyber-world becomes
increasingly embedded into power grids, the risks of this inevitable evolution
become serious. In this paper, we present a risk mitigation strategy, based on
dynamic state estimation, to eliminate threat levels from the grid's unknown
inputs and potential cyber-attacks. The strategy requires (a) the potentially
incomplete knowledge of power system models and parameters and (b) real-time
PMU measurements.
  First, we utilize a dynamic state estimator for higher order depictions of
power system dynamics for simultaneous state and unknown inputs estimation.
Second, estimates of cyber-attacks are obtained through an attack detection
algorithm. Third, the estimation and detection components are seamlessly
utilized in an optimization framework to determine the most impacted PMU
measurements. Finally, a risk mitigation strategy is proposed to guarantee the
elimination of threats from attacks, ensuring the observability of the power
system through available, safe measurements. Case studies are included to
validate the proposed approach. Insightful suggestions, extensions, and open
problems are also posed.
