  Wide-area control is an effective mean to reduce inter-area oscillations of
large power systems. Its dependence on communication of remote measurement
signals makes the closed-loop system vulnerable to cyber attacks. This paper
develops a framework to analyze and quantify resilience of a given wide-area
controller under disruptive attacks on certain communication links. Resilience
of a given controller is measured in terms of closed-loop eigenvalues under the
worst possible attack strategy. The computation of such a resilience index is
challenging especially for large-scale power systems due to the discrete nature
of the attack strategies. To address the challenge, we propose an
optimization-based formulation and a convex relaxation approach to facilitate
the computation. Conditions under which the relaxation is exact are derived and
an efficient algorithm with guaranteed convergence is also developed. The
proposed framework and the algorithm allow us to quantify resilience for given
wide-area controllers and also provide sufficient conditions to guarantee
closed-loop stability under all possible communication attacks. Simulations are
performed on the IEEE 39-bus system to illustrate the proposed resilience
analysis and computation framework.
