A Case Study on Modeling Adequacy of a Grid with Subsynchronous Oscillations Involving IBRs

TL;DR

This paper investigates the modeling adequacy of power grids with renewable resources and grid-forming converters, highlighting the importance of transmission line dynamics in capturing subsynchronous oscillations through eigenvalue analysis.

Contribution

It revisits the space-phasor-calculus in the d-q frame for stability analysis and demonstrates the limitations of quasistationary models in representing subsynchronous oscillations.

Findings

SPC models with transmission line dynamics capture SSOs effectively.

QPC models neglecting line dynamics fail to predict SSOs.

Eigenvalue analysis confirms the necessity of including transmission dynamics.

Abstract

A case study on modeling adequacy of a grid in presence of renewable resources based on grid-forming converters (GFCs) is the subject matter of this paper. For this purpose, a 4-machine 11-bus IEEE benchmark model is modified by considering GFCs replacing synchronous generators that led to unstable subsynchronous oscillations (SSOs). We aim to: (a) understand if transmission network dynamics should be considered in such cases, (b) revisit the space-phasor-calculus (SPC) in d-q frame under balanced condition that captures such phenomena and lends itself to eigenvalue analysis, and (c) emphasize limitations of such models while underscoring their importance for large-scale power system simulations. Time-domain and frequency-domain results from SPC and quasistationary phasor calculus (QPC) models are compared with electromagnetic transient (EMT)-based simulations. It is shown that models with transmission line dynamics in SPC framework can capture the SSO mode while QPC models that neglect these dynamics fail to do so.