Analysis on the Influencing Factors of SSO of Direct-Drive Wind Farm via MMC-HVDC Transmission

This paper focuses on studying the issue of subsynchronous oscillation (SSO) caused by direct-drive wind farms via flexible DC transmission. The analysis utilizes the theorem for impedance-based system stability analysis to derive a criterion for evaluating the damping stability of the equivalent circuit. Using this criterion, the relationship between the damping characteristics of the equivalent circuit and the control systems, such as the grid-side converter (GSC) for wind turbine control and the modular multilevel converter (MMC) control system, is examined. The influencing of control parameters on SSO characteristics is investigated. To validate the findings, a simulation model of the direct-drive wind farm transmission system via a modular multilevel converter-based high-voltage DC (MMC-HVDC) is built on the PSCAD/EMTDC simulation platform, and electromagnetic transient simulation analysis and verification are conducted.