Overview
Frequency stability assessment in high-renewable power systems faces complexity due to increasingly large active-power disturbances exhibiting diverse time scales. A response-based frequency stability assessment method has been developed to address this challenge. This method uses disturbance power, inferred from generator electrical responses, to provide a unified treatment for multi-scale disturbances.
Research Context
High-renewable power systems are characterized by active-power disturbances that are becoming larger and occur across a wider range of time scales. This trend complicates the assessment of frequency stability, particularly when confronting unanticipated events. The need exists for robust methods that can effectively evaluate frequency stability under these evolving conditions.
Approach
The proposed response-based method involves several sequential steps for frequency stability assessment:
Disturbance Classification
Unanticipated disturbances are initially classified into two broad categories: short-term events and permanent events. Permanent disturbances are further refined into specific types: step disturbances, second-level slope disturbances, and minute-level slope disturbances.
Unified Disturbance-Power Model Construction
Based on measured power responses from generator groups, a unified disturbance-power model is constructed. This model serves to identify the disturbance type online and quantify its intensity. Intensity quantification is achieved through evaluation of the disturbance power and its rate of change.
Analytical Frequency-Response Model Derivation
Analytical frequency-response models are derived specifically for each identified disturbance class. These models form the basis for subsequent stability assessments.
Stability Assessment for Step Disturbances
For step disturbances, the method determines the maximum tolerable disturbance power. This determination is made subject to constraints related to both steady-state and transient frequency deviation. A safety-margin index is also defined for this disturbance type.
Stability Assessment for Slope-Type Disturbances
For slope-type disturbances, an improved system frequency response (SFR) model is employed. Additionally, the rotor motion equation, particularly after the exhaustion of primary frequency regulation, is utilized. These elements are combined to compute the over-limit time of frequency deviation.
Findings
The proposed response-based assessment method demonstrated its effectiveness and accuracy. Validation was conducted on the CSEE-FS frequency-stability benchmark system. This validation indicates the method's capability for quantitative frequency stability assessment within high-renewable power systems.
Why This Matters
The method provides a unified framework for assessing frequency stability under various types and scales of active-power disturbances in high-renewable power systems. By quantifying disturbance intensity and predicting frequency deviation, it offers a systematic approach to manage challenges posed by increasing renewable energy integration.