A Unified Analytical Method to Quantify Three Types of Fast Frequency Response from Inverter-based Resources

TL;DR

This paper introduces an analytical method to accurately predict the lowest system frequency after contingencies by considering three types of fast frequency responses from inverter-based resources, aiding in system stability analysis.

Contribution

It develops a unified closed-form analytical approach to quantify three types of fast frequency response from inverter-based resources considering governor dynamics.

Findings

Accurately predicts frequency nadir in IEEE 39-bus system simulations.

Considers three types of FFR: step, proportional, and derivative responses.

Provides fast and reliable frequency response estimation.

Abstract

With more inverter-based resources (IBRs), our power systems have lower frequency nadirs following N-1 contingencies, and undesired under-frequency load shedding (UFLS) can occur. To address this challenge, IBRs can be programmed to provide at least three types of fast frequency response (FFR), e.g., step response, proportional response (P/f droop response), and derivative response (synthetic inertia). However, these heterogeneous FFR challenge the study of power system frequency dynamics. Thus, this paper develops an analytical frequency nadir prediction method that allows for the consideration of all three potential forms of FFR provided by IBRs. The proposed method provides fast and accurate frequency nadir estimation after N-1 generation tripping contingencies. Our method is grounded on the closed-form solution for the frequency nadir, which is solved from the second-order system frequency response model considering the governor dynamics and three types of FFR. The simulation results in the IEEE 39-bus system with different types of FFR demonstrate that the proposed method provides an accurate and fast prediction of the frequency nadir under various disturbances.