Analysis of Frequency Oscillation Caused by AGC in Hydro-Dominant Power Grids using Piecewise Linearization Method

A piecewise linearization model is developed for the analysis of ultra-low frequency oscillation, taking the nonlinearity of governor deadband and the automatic generation control (AGC) into considerations. Firstly, the ultra-low frequency oscillations occurred in actual power grids are discussed in depth. Then, based on the piecewise linearization model developed, the AGC-excited frequency mode is calculated and key factors that influence the frequency stability are analyzed using the eigenvalue approach. Results show that the governor deadband introduces a frequency mode that likely to be excited by large frequency bias coefficient B of the AGC system. To avoid this frequency oscillation, it is advised that B should be properly tuned under the situation when only the secondary frequency regulation is activated.