  In modern power systems, the operating point, at which the demand and supply
are balanced, may take different values due to changes in loads and renewable
generation levels. Understanding the dynamics of stressed power systems with a
range of operating points would be essential to assuring their reliable
operation, and possibly allow higher integration of renewable resources. This
letter introduces a non-traditional way to think about the stability assessment
problem of power systems. Instead of estimating the set of initial states
leading to a given operating condition, we characterize the set of operating
conditions that a power grid converges to from a given initial state under
changes in power injections and lines. We term this problem as "inverse
stability", a problem which is rarely addressed in the control and systems
literature, and hence, poorly understood. Exploiting quadratic approximations
of the system's energy function, we introduce an estimate of the inverse
stability region. Also, we briefly describe three important applications of the
inverse stability notion: (i) robust stability assessment of power systems
w.r.t. different renewable generation levels, (ii) stability-constrained
optimal power flow (sOPF), and (iii) stability-guaranteed corrective action
design.
