Low-frequency Resonances in Grid-Forming Converters: Causes and Damping Control

TL;DR

This paper investigates the causes of low-frequency resonances in grid-forming converters and reviews control strategies for damping these resonances, supported by experimental validation under various grid conditions.

Contribution

It provides a comprehensive analysis of resonance causes in GFM-VSC systems and critically reviews recent damping control methods with experimental results.

Findings

Identification of control interactions causing SR and SSR

Evaluation of damping control effectiveness through experiments

Insights into stabilizing control strategies for GFM-VSC

Abstract

Grid-forming voltage-source converter (GFM-VSC) may experience low-frequency resonances, such as synchronous resonance (SR) and sub-synchronous resonance (SSR), in the output power. This paper offers a comprehensive study on the root causes of low-frequency resonances with GFM-VSC systems and the damping control methods. The typical GFM control structures are introduced first, along with a mapping between the resonances and control loops. Then, the causes of SR and SSR are discussed, highlighting the impacts of control interactions on the resonances. Further, the recent advancements in stabilizing control methods for SR and SSR are critically reviewed with experimental tests of a GFM-VSC under different grid conditions.