Power System Frequency Security Index Considering All Aspects of Frequency Profile

Frequency security is an essential issue in power system operation and planning, especially with the increasing penetration level of intermittent and non-synchronous energy sources, which causes insufficiency of inertial and primary frequency responses. Therefore, various studies must observe the frequency security in the problem formulation as objective function and/or constraints. This letter proposes a Frequency Security Index (FSI), which determines the frequency security based on all aspects of the frequency profile. This index presents a quantitative percentage for the frequency security in order to specify the relative distance from the insecure (0%), secure (100%), and absolute secure (200%) conditions. The FSI considers transient and steady-state aspects of frequency security based on the boundaries related to each power system requirements and standards. The applicability, correctness, and sufficiency of the proposed index are demonstrated based on the numerical results of a real large-scale power system.