Discovery and Characterization of Cross-Area and Intra-Area SSOs Sensitive to Delay in Droop Control of Grid-Forming Converters

TL;DR

This paper identifies and characterizes new cross-area and intra-area subsynchronous oscillations in power grids with grid-forming converters, highlighting the impact of droop control delays on stability through frequency-domain analysis and simulations.

Contribution

It introduces the phenomenon of cross-area SSOs in grids with 100% droop-controlled GFCs and analyzes the effects of droop delay on their stability.

Findings

Discovery of cross-area SSOs in GFC-dominated grids

Frequency-domain characterization of oscillatory modes

Validation through electromagnetic transient simulations

Abstract

Subsynchronous oscillations (SSOs) involving grid-forming converters (GFCs) are in a less familiar territory of power system dynamics. This letter reports a new phenomenon namely cross-area SSOs in grids with 100% droop-controlled GFC-based renewable penetration, which was discovered during our study on evaluating the adequacy of quasistationary phasor calculus (QPC) and space phasor calculus (SPC)-based models in capturing SSOs. We present frequency-domain characterization of such oscillatory modes in addition to intra-area SSOs in grids involving GFCs and study the impact of a delay in power-frequency droop feedback loop in regards to their stability. Electromagnetic transient (EMT) simulations validate our findings.