Characteristics of Subsynchronous Oscillation Power Propagation in the Large-scale Wind Farm Integrated System

Subsynchronous oscillation (SSO) caused by the large-scale wind farm integrated system has become an important issue which would threaten the security and stability of power system. Some practical cases have shown that SSO can propagate to more than three hundred kilometers through multiple voltage levels. Many studies have been focused on the issue, but there is still a lack of research on SSO power propagation characteristics. The characteristics of SSO power propagation in the large-scale wind farm integrated system was studied in the paper. Firstly, the expression of SSO power was analyzed by using the instantaneous power definition. Secondly, the characteristics of SSO power propagation were quantitatively studied by circuit analysis and derivation. Finally, simulations were carried out to verify conclusions of theoretical analysis. It is demonstrated that SSO power contains subsynchronous component and DC component when system is operating symmetrically. Otherwise it also contains supersynchronous components which amplitude is proportional to the degree of system operation asymmetry. And it is found that SSO power propagation is affected by both power flow and line impedance characteristics. Then the SSO power propagation influence factor and diversion coefficient are defined to quantify the dominant influencing factors and propagation paths of SSO power propagation under different operating conditions. © 2020 Chin. Soc. for Elec. Eng.