Mechanism and Suppression Control of Wideband Oscillations in MMC-HVDC Connected Offshore Wind Farms

High-voltage dc (HVDC) transmission is preferred for power transfer of large-scale long-distance offshore wind farms, and practical projects based on the modular multilevel converter (MMC) for wind farms have been globally put into operation or under construction. In China, several key projects with the capacity of more than 1000 MW are being built. However, the wideband oscillation phenomena arising from the interactions between the wind farm and the MMC-HVDC system have been frequently observed in practical systems. This paper will focus on the mechanism and suppression control of wideband oscillations in MMC-HVDC connected offshore wind farms. First, the aggregation modeling of offshore wind farms and impedance modeling of MMC including internal dynamics and all control loops are conducted. On this basis, the mechanisms of wideband oscillations in the offshore wind farm-MMC interconnected system are revealed with special focus on the discussion of the main influencing factors. Then, an adaptive suppression control method for wideband oscillations is proposed. Finally, case studies will be carried out on a practical project in China to validate the effectiveness of the mechanism analysis and suppression control of wideband oscillations.