  We propose a Koopman operator-based surrogate model for propagating parameter
uncertainties in power system nonlinear dynamic simulations. First, we augment
the a priori known state-space model by reformulating parameters deemed
uncertain as pseudo-state variables. Then, we apply the Koopman operator theory
to the resulting state-space model and obtain a linear dynamical system model.
This transformation allows us to analyze the evolution of the system dynamics
through its Koopman eigenfunctions, eigenvalues, and modes. Of particular
importance for this letter, the obtained linear dynamical system is a surrogate
that enables the evaluation of parameter uncertainties by simply perturbing the
initial conditions of the Koopman eigenfunctions associated with the
pseudo-state variables. Simulations carried out on the New England test system
reveal the excellent performance of the proposed method in terms of accuracy
and computational efficiency.
