Modal-based prediction of power system frequency response and frequency nadir

Abstract

This paper introduces a novel approach for predicting system frequency response (SFR) and frequency nadir based on modal analysis. By decomposing the full system dynamic response, the method identifies dominant modes based on their participation in frequency behavior and derives a closed-form expression for the frequency trajectory. Unlike traditional approaches based on the Average System Frequency (ASF) model, this method captures the true system dynamics and avoids oversimplified representations. The dominant modes exhibit low sensitivity to system parameters, enabling robust and accurate estimations across diverse operating conditions. The proposed approach is tested on two benchmark systems as well as the Salvadoran transmission planning network, demonstrating its scalability, precision, and adaptability. This methodology represents a shift from observing a simplified average system frequency response to a more detailed analysis focusing on system dynamics.