Sub-synchronous control interaction between direct-drive PMSG-based wind farms and compensated grids

Abstract

Previous researches suggested that the direct-drive permanent magnetic synchronous generator (PMSG)-based wind farms are immune from sub-synchronous control interaction (SSCI). However, since the occurrence of emerging sub-synchronous oscillation (SSO) caused by PMSG-based wind farm connected to a weak AC network, it is of great significant to re-investigate this SSCI problem. To address it, a small-signal model of target system is established first, then modal analysis is conducted to delve into the dynamic interaction between PMSG and compensated network, and the time domain simulation is performed to verify modal analysis results. The results of the paper reveal that PMSG connected to compensated grid could excite an emerging SSCI, which is caused by the dynamic interaction of converters and series compensated line, and the oscillation frequency is strongly related to the electrical resonance frequency. The major contributions of the paper include: (1) re-discussion of the SSCI immunity of PMSG-based system and re-identification of the turbine types which are susceptible to SSCI, (2) analysis on frequency characters of the emerging SSCI, (3) investigation of decoupling effect between machine and grid.