Sub-synchronous Oscillations in Power Systems Caused by Grid-connected Wind Farms-A Survey of Mechanism Studies

Sub-synchronous oscillation (SSO) incidents caused by dynamic interaction between wind farms and power system grids can threaten safe and reliable operations. This paper investigates mechanism studies of SSOs in power systems induced by grid-connected wind farms. First, characteristics of several severe SSO incidents encountered by real power systems caused by grid-connected wind farms are introduced. Second, in terms of principles and responses, this paper illustrates the most commonly adopted mechanism investigation methods for SSOs, which include impedance-based analysis (IMA) and the openloop modal analysis (OMA) methods. Systematic reviews that summarize existing studies using the IMA and OMA methods are discussed in this paper. Furthermore, a discussion of the current research gaps in the investigation of SSOs in power systems caused by grid-connected wind farms is presented.