Impedance characteristics of DFIGs considering the impacts of DFIG numbers and locations and its application on SSR analysis

Sub-synchronous resonance (SSR) occurred in the power system with both Doubly Fed Induction Generators (DFIGs) and series-compensated lines. There have been several papers focusing on the analysis of such SSR phenomenon. To the authors' knowledge, the impacts of DFIG numbers and locations are seldom considered in existing papers. In this paper, the impedance characteristics of DFIGs under different wind speeds and with different numbers are analyzed. The contributions to be included in the paper are as following: 1) the impedance of N DFIGs is roughly equal to 1/N of the impedance of one DFIG. The relationship between SSR damping and the DFIG number could be monotonic or nonlinear in case of different series-compensated line parameters. 2) The influence of SSR characteristics different under different wind speeds for two wind farms is different. The wind speed of the closer wind farm has a greater impact of the system stability.