Influence and Analysis of PFC of DFIG on the Ultra-Low Frequency Oscillations Mode of Power System

The large-scale integration of renew abIes into power systems leads to the decrease of system inertia. Grid codes require renewable generators, e.g., wind turbines (WTs), to actively participate system frequency regulation. Whereas, the addition of frequency control inevitably induces the electromechanical interactions between WTs and power systems. In this paper, the influence of primary frequency control (PFC) of DFIG on ultra-low frequency oscillation of power system is studied. Firstly, a modified two-area four-machine test system is built, via numerical simulations, we identify that high gain of DFIG PFC can possibly stimulate an ultra-low frequency oscillation around 0.06 Hz. Subsequently, a small-signal model of such system is constructed and a closer analysis on this phenomenon is carried by eigenvalue and participation factor analysis. The key control parameters related to this mode is identified, and investigated by eigenvalue sensitivity analysis. Time domain analysis are conducted to verify the effectiveness of the analysis above.