Mitigation of subsynchronous oscillation in a VSC-HVDC connected offshore wind farm integrated to grid

Abstract This paper focuses on analyzing and mitigating subsynchronous oscillations (SSO) in a doubly-fed induction generator (DFIG)-based offshore wind farm when connected to power grid through voltage source converter based HVDC (VSC-HVDC). Two dominant kinds of oscillation modes are found by modal analysis. One is subsynchronous shaft torsional oscillation (SSTO). However, only a little information exists in published literature regarding SSTO of an offshore wind farm. The other one, which in this paper is named as subsynchronous equipment interaction (SSEI), is due to the interaction between the converter controller of VSC-HVDC and that of wind farm. Research about SSEI is rare and lacks comprehensiveness. For further analysis and mitigation of SSO, participation factor (PF) analysis is conducted in this paper to find variables strongly correlated with SSTO and SSEI. Major contributions of this paper are (1) qualitative principle analysis of these two modes, (2) investigation of the influence of strongly-correlated variables on the oscillation characteristics of each mode and (3) application of damping controllers to comprehensively mitigate SSTO and SSEI.