  This paper aims to identify and analyze the initial contingencies or
disturbances that could lead to the worst-case cascading failures of power
grids. An optimal control approach is proposed to determine the most disruptive
disturbances on the branch of power transmission system by regarding the
disturbances as the control inputs. Moreover, protective actions such as load
shedding and generation dispatch are taken into account in a convex
optimization framework to prevent the cascading outages of power grids. In
theory, the necessary conditions for identifying the most disruptive
disturbances are obtained by solving an integrated system of algebraic
equations. Finally, numerical simulations are carried out to validate the
proposed approach on the IEEE RTS 24 Bus System.
