A Method to Determine the Distance to the Critical Oscillatory Stability Limit in Terms of Active Power Injections

This article presents a method to derive meaningful margins that provide information regarding the distance to critical oscillatory stability limits. The proposed method relies on modal torque concepts which allows to reduce the eigenvalue problem to a problem involving only generator torque and speed oscillations. The reduced problem size and the sparsity of the involved matrices makes it suitable for the application to large power systems. The algorithm relies on deriving the first order eigenvalue sensitivities in respect to perturbations of generator machine active power injections based on power flow quantities. The viability of the method is demonstrated at the example of the Nordic power system, showing the capability of determining critical operation well away from the actual critical stability limit.