Frequency Nadir Estimation Using the Linear Characteristics of Frequency Control in Power Systems

With the increasing integration of inverter-based resources, the contribution of synchronous generators to power grids has decreased, resulting in a reduction in system inertia. Currently, acquiring the reserve power to mitigate the volatility associated with renewable-energy sources are difficult. Hence, evaluating the frequency stability of power systems and formulating operational and planning strategies based on these evaluations are becoming increasingly important. In this paper, we propose the definition and formalization of the frequency nadir index (FNI) by identifying the linear characteristics of inertia, frequency regulating reserve space (FRRS), and governor free (G/F) reserve in relation to frequency nadir, particularly under assumed contingencies such as generator dropout and sudden load fluctuation. Furthermore, we present an effective methodology for evaluating frequency stability using the FNI equation by extracting inertia, FRRS, and G/F reserve information from the power-system data. This approach is straightforward and efficiently computes the frequency nadir based on the size of the generator failure using readily available power-system data within a short timeframe.