  Power grids normally operate at some stable operating condition where power
supply and demand are balanced. In response to emergency situations, load
shedding is a prevailing approach where local protective devices are activated
to cut a suitable amount of load to quickly rebalance the supply demand and
hopefully stabilize the system. This traditional emergency control results in
interrupted service with severe economic damage to customers. Also, such
control is usually less effective due to the lack of coordination among
protective devices. In this paper, we propose a novel structural emergency
control to render post-fault dynamics from the critical/emergency fault-cleared
state to the stable equilibrium point. This is a new control paradigm that does
not rely on any continuous measurement or load shedding, as in the classical
setup. Instead, the grid is made stable by discretely relocating the
equilibrium point and its stability region such that the system is
consecutively attracted from the fault-cleared state back to the original
equilibrium point. The proposed control is designed by solving linear and
convex optimization problems, making it possibly scalable to large-scale power
grids. Finally, this emergency control scheme can be implemented by exploiting
transmission facilities available on the existing grids.
