低频振荡是影响电力系统稳定运行的一个重要方面。阐述了低频振荡产生的机理和分析方法，利用Hopf分歧理论，针对一个四阶模型的单机无穷大系统，分析了在临界点附近时可能出现的非线性奇异现象。研究表明：由于分歧的存在，导致系统稳定性在临界点附近出现奇异，从而影响了电力系统的稳定域。

LFO (Low Frequency Oscillation) is a main aspect that affects power system stability. In this paper, the inherent reason that causes LFO is discussed.With Hopf bifurcation theory, it is analyzed that the nonlinear singularity phenomenon happens close to the critical points in a single-infinite power system of four-rank model. The study indicates that because of the Hopf bifurcation, singularity phenomenon in the power system happens close to the critical points, which affects the steady bound.