Frequency Stability Evaluation Based on Conservative Piecewise-Linearized Frequency Nadir Model in South Korea

Synchronous generators (SGs) provide the inertia and reserve power required to ensure frequency stability in the power system, while renewable resources do not contribute effectively. Maintaining frequency stability is challenging because of the increase in renewable resources and corresponding decline in SGs in response to climate change. Therefore, developing grid operation and planning strategies based on frequency stability evaluation has become increasingly important. In South Korea, frequency stability is evaluated based on frequency nadir during disturbances such as generator failures. This paper proposes a conservative piecewise-linearized frequency nadir (C-PLFN) model based on linearized relationships between the frequency nadir and system inertia, frequency regulating reserve space, governor-free reserve (GFR), and load size. The main features of the proposed methodology include linear regression on the frequency nadir against datasets of system inertia and GFR by load sizes, linear regression on the coefficients in the equation obtained by load sizes, and formalizing the C-PLFN model. This method was validated using the 2024 power system data for South Korea and the transmission security management data saved as real-time steady-state data for power system simulation for engineering simulations in South Korea.