Study on subsynchronous oscillation in D-PMSGs-based wind farm integrated to power system

In recent years, the subsynchronous oscillation (SSO), which occurs in direct-drive permanent magnetic synchronous generators (D-PMSGs)-based wind farm, has great impact on the stability of power system. The different parameters and operation conditions of D-PMSGs lead to the subsynchronous interaction (SSI) among D-PMSGs. What is more, the SSI will influence the SSO characteristics of the system of D-PMSGs-based wind farm integrated to AC network. Here, considering the difference of parameters or operation conditions among D-PMSGs in the wind farm, eigenvalue analysis, based on the small-signal state-space model of two aggregated D-PMSGs which are equivalent to wind farm, is carried out. Then the stability and the SSI between D-PMSGs of the equivalent system can be studied, and the dominant D-PMSG can be determined based on the participation factors. Lastly, the detailed electromagnetic transient simulation model of D-PMSGs equivalent system is built in PSCAD/EMTDC. The simulation is conducted to corroborate the eigenvalue analysis. The result shows that an obvious SSI exists between two aggregated D-PMSGs. Furthermore, the different SSO characteristics among D-PMSGs in the wind farm indicate the study of SSO problem based on an aggregated D-PMSGs model may leave out some useful information.