Determination of Sub Synchronous Control Interaction between Wind Turbines and Series Compensated Transmission Lines

In this paper, a modified frequency impedance scanning tool is developed to scan wind turbine side impedance at various frequencies.  Voltage harmonic injection technique by retaining the fundamental frequency is used to determine the impedances at any given subsynchronous frequencies.  Additionally, the tool is designed to incorporate the entire frequency range of interest in a single simulation rather than the traditional multi-run or looped frequency scanning techniques.  The principle of frequency scanning analysis is used to determine the risk of sub-synchronous control interaction (SSCI) before an interconnection of wind farm. The tool measures the impedance of non-linear models containing power electronic devices (such as wind turbines) at sub-synchronous frequencies (SSF).  The tool is validated with a passive RLC circuit at a known resonance frequency in PSCAD and also for non-linear systems consisting of representative Doubly Fed Induction Generator (DFIG) wind turbine model and a designed SSCI test grid.   The tool developed is used to determine the behavior of a representative DFIG wind turbine at sub-synchronous frequencies and its susceptibility to SSCI events under various operating conditions.  Sensitivity of various wind parameters at wind farm level on the impedance exhibited by the wind generation plant is studied.