Subsynchronous control interaction studies in DFIG-based wind farms using selective modal analysis

Abstract

In this paper the Selective Modal Analysis (SMA) method is used for reproducing the eigenvalues involved in subsynchronous control interactions (SSCI) between DFIG-based wind farms and series compensated transmission lines. The SMA method provides a reduced system matrix containing a desired part of the eigenstructure of a system without computing the eigenvalues and eigenvectors of the full system. The key concept for obtaining such reduced matrix resides in an appropriate identification of a subset of state variables and eigenvalues of the system. The intrinsic problems in identifying the corresponding subset for analyzing the SSCI phenomenon are explored and illustrated using a simplified radial system. In addition, a systematic approach for obtaining a subset with minimum dimension is proposed. The methodology consists in a two-phase iterative procedure that reduces the computational load and promotes the convergence of the SMA method to the desired eigenstructure. The proposed algorithm is validated on a relative large power system derived from a practical network.