Analysis of Subsynchronous Oscillation Caused by Integration of New Wind Farm via MMC-HVDC

The integration of new wind farm via modular multilevel converter based high-voltage direct current (MMC-HVDC) will lead to subsynchoronous oscillation (SSO). The SSO will activate the protection of MMC-HVDC, and then the whole system will shut down. In order to address this problem, the propagation and distribution of SSO in the whole system are derived. First, the model of wind farms integrated into the power grid through MMC-HVDC is established. Second, the characteristics of SSO caused by the integration of new wind farm is analyzed. The process of propagation of SSO from wind farms to MMC-HVDC is derived. By calculating the instantaneous power of the MMC bridge arms, the frequencies of SSO components present in the system are calculated. The SSO components frequency relationship among wind farm, MMC-HVDC and power grid is revealed. Finally, the correctness of the theoretical analysis is validated by time-domain simulations.