Research Overview of Sub-synchronous Oscillation in DFIG-Based Wind Farm Connected to Complex System

The sub-synchronous oscillation(SSO) triggered by the large-scale access of wind power and power electronics have brought new challenges to the safe and stable operation of power system. When the doubly-fed induction generator(DFIG) is connected to weak grid by series compensation or connected to the multi-infeed DC system, there is a risk of SSO of wind turbines. Therefore, it is urgent to reveal the internal mechanism and propose mitigation strategies. Firstly, this paper introduces the equivalence modeling methods of the DFIG-based wind farm, including controlled source aggregation equivalence method, equivalent parameter equivalence method, single impedance equivalence method considering the collector system, and multi-machine equivalence method. Then, the main research methods of SSO in DFIG-based wind farm connected to complex system are discussed, including eigenvalue analysis method, impedance analysis method, frequency scan method, complex torque coefficient method, and time-domain simulation method. On this basis, the mitigation measures of SSO are summarized, which are divided into power-side mitigation method and grid-side mitigation method. Finally, the future research direction of SSO in DFIG-based wind farm connected to complex system is prospected to provide useful references for the long-distance safe and stable transmission of large-scale DFIG-based wind farms.