Response-Based Frequency Stability Assessment under Multi-Scale Disturbances in High-Renewable Power Systems

In high-renewable power systems, active-power disturbances are becoming larger and exhibit increasingly diverse time scales, which complicates frequency stability assessment under unanticipated events. This paper presents a response-based frequency stability assessment method that uses disturbance power, inferred from generator electrical responses, to provide a unified treatment of multi-scale disturbances. Unanticipated disturbances are first classified into short-term and permanent events; permanent disturbances are further divided into step, second-level slope and minute-level slope disturbances. Based on the measured power responses of generator groups, a unified disturbance-power model is constructed to identify the disturbance type online and to quantify disturbance intensity through the disturbance power and its rate of change. Analytical frequency-response models are then derived for each disturbance class. For step disturbances, the maximum tolerable disturbance power is obtained under steady-state and transient frequency deviation constraints, and a safety-margin index is defined. For slope-type disturbances, an improved system frequency response (SFR) model and the rotor motion equation after exhaustion of primary frequency regulation are used to compute the over-limit time of frequency deviation. The proposed response-based assessment method is validated on the CSEE-FS frequency-stability benchmark system, demonstrating its effectiveness and accuracy for quantitative frequency stability assessment in high-renewable power systems.