  This paper considers power networks governed by swing nonlinear dynamics and
subject to disturbances. We develop a bilayered control strategy for a subset
of buses that simultaneously guarantees transient frequency safety of each
individual bus and asymptotic stability of the entire network. The bottom layer
is a model predictive controller that, based on periodically sampled system
information, optimizes control resources to have transient frequency evolve
close to a safe desired interval. The top layer is a real-time controller
assisting the bottom-layer controller to guarantee transient frequency safety
is actually achieved. We show that control signals at both layers are Lipschitz
in the state and do not jeopardize stability of the network. Furthermore, we
carefully characterize the information requirements at each bus necessary to
implement the controller and employ saddle-point dynamics to introduce a
distributed implementation that only requires information exchange with up to
2-hop neighbors in the power network. Simulations on the IEEE 39-bus power
network illustrate our results.
