Modeling and Analysis of Low-Frequency Oscillations in Thermal Power Unit Governing Systems Considering Small Frequency Deviation Amplification

With the continuous reduction in equivalent inertia in modern power systems, thermal power units are required to provide faster and more sensitive primary frequency regulation. Under this background, small frequency deviation amplification (compensation) has been widely implemented in governing systems. However, while such high-gain control improves frequency response performance, it may significantly deteriorate system damping and even induce low-frequency oscillations (LFO). The underlying mechanism, however, has not been fully clarified from a theoretical perspective. To address this issue, a refined electromechanical coupled model of a thermal power unit governing system incorporating small frequency deviation amplification is established, and the corresponding linearized model is derived. Based on the damping torque analysis method, the influence of amplification gain on mechanical damping is rigorously analyzed in the frequency domain, and the fundamental mechanism leading to damping degradation is revealed. Furthermore, time-domain simulations are conducted to compare system dynamic responses under different compensation parameter settings. The results indicate that the amplification gain has a significant impact on LFO characteristics. Improper parameter settings can directly reduce system damping and trigger oscillations.