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

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.