Dominant mode identification and influence mechanism investigation of frequency oscillations as affected by automatic generation control

Several frequency oscillation events have recently been observed in practical power grids, which are strongly related with dynamic process of AGC (automatic generation control). This kind of oscillations are caused by the phase relation mismatching between mechanical powers and rotational speeds and the detailed dynamic performance and oscillation mechanism are not clear and deserve in-depth investigations. Motivated by this, this paper establishes the state-space model of multi-area AGC systems containing different kinds of generator units and time-scale dynamics. Without distinguishing AGC and PFR (primary frequency regulation) modes, Homotopy method is applied to identify the dominant mode and thus analyze the key influencing factors of frequency oscillations affected by AGC dynamics. The method can clearly establish the congruent relationship between eigenvalues and state variables and is more rapid and intuitive to identify the dominant mode for AGC oscillations. The correctness and feasibility of the proposed method are validated by time-domain simulations and results analysis. Finally, simulations are performed in single-area as well as four-area system based on real data to demonstrate the proposed model and method. And relevant parameter influence mechanism and oscillation performances are investigated for AGC system oscillations.