  The increasing penetration of inverter based renewable generation (RG) in the
form of solar photo-voltaic (PV) or wind has introduced numerous operational
challenges and uncertainties. According to the standards, these generators are
made to trip offline if their operating requirements are not met. In an RG-rich
system, this might alter the system dynamics and/or cause shifting of the
equilibrium points to the extent that a cascaded tripping scenario is
manifested. The present work attempts at avoiding such scenarios by estimating
the constrained stability region (CSR) inside which the system must operate
using maximal level set of a Lyapunov function estimated through sum of squares
(SOS) technique. A time-independent conservative approximation of the LVRT
constraint is initially derived for a classical model of the power system. The
proposed approach is eventually validated by evaluating the stability of a 3
machine test system with trip-able RG.
