# High-Frequency Oscillation Suppression Strategy for VSG MMC-HVDC Integrated Offshore Wind Farms Considering Frequency Coupling

## TL;DR

This paper identifies a new high-frequency coupling issue in wind farms using VSG control and proposes a suppression strategy to stabilize the system.

## Contribution

The novel contribution is the discovery of high-frequency coupling in VSG-controlled systems and a new suppression strategy using a band-stop filter.

## Key findings

- A significant high-frequency-range frequency coupling between the GSC and the VSG-controlled WFMMC was discovered.
- The proposed band-stop filter strategy effectively suppresses high-frequency oscillations in various operating conditions.

## Abstract

What are the main findings?
A significant high-frequency-range frequency coupling between the GSC and the VSG-controlled WFMMC has been discovered, which critically reshapes their positive-sequence impedances.Based on the identified key control loops responsible for frequency coupling, a high-frequency oscillation suppression strategy incorporating a band-stop filter in the WFMMC voltage sampling loop is proposed, with consideration of frequency coupling.

A significant high-frequency-range frequency coupling between the GSC and the VSG-controlled WFMMC has been discovered, which critically reshapes their positive-sequence impedances.

Based on the identified key control loops responsible for frequency coupling, a high-frequency oscillation suppression strategy incorporating a band-stop filter in the WFMMC voltage sampling loop is proposed, with consideration of frequency coupling.

What are the implications of the main findings?
This finding compels a revision of conventional stability theory by revealing that frequency coupling under VSG control extends into the high-frequency range, thereby mandating its incorporation into the design of high-frequency oscillation suppression strategies, unlike the conventional V-f control.The proposed strategy effectively suppresses the frequency coupling between the GSC and the VSG-controlled WFMMC, thereby mitigating high-frequency oscillations in the system induced by such coupling under various challenging operating conditions.

This finding compels a revision of conventional stability theory by revealing that frequency coupling under VSG control extends into the high-frequency range, thereby mandating its incorporation into the design of high-frequency oscillation suppression strategies, unlike the conventional V-f control.

The proposed strategy effectively suppresses the frequency coupling between the GSC and the VSG-controlled WFMMC, thereby mitigating high-frequency oscillations in the system induced by such coupling under various challenging operating conditions.

In MMC-HVDC-integrated offshore wind farms, the Wind-Farm-side MMC (WFMMC) is increasingly adopting Virtual Synchronous Generator (VSG) control to provide active support. However, this control strategy may introduce high-frequency oscillations that cannot be predicted by conventional stability analysis. Existing suppression strategies, designed for WFMMC under conventional V-f control, fail to account for frequency coupling effects in the high-frequency range, making it difficult to effectively analyze or suppress such oscillations. To address this issue, this article reveals a significant high-frequency-range frequency coupling effect between the wind turbine’s Grid-Side Converter (GSC) and the VSG-controlled MMC, which is distinct from systems with conventional V-f control. It is further identified that the asymmetric control structure introduced by the VSG control and control delay are the key factors driving this coupling. Based on this finding, an oscillation suppression strategy incorporating a band-stop filter in the WFMMC voltage sampling loop is proposed. Time-domain simulations demonstrate the effectiveness of this strategy under various operating conditions.