Research On Disturbance Resonant Oscillation Mechanism Of Power System Low Frequency Oscillations

With China's power system interconnection and the development of the electricity market, security incidents of Small Signal Stability in power system occur more and more and it brings about a lot of hidden dangers in safe operation of the power system. When the generators are lack in damping torque, the rotors among these generators are easily to have relative swings, leading to durative low-frequency oscillations (LFO) on transmission lines. This LFO is a typical phenomenon about deficiency of small signal stability margin. Moreover, some unknown low-frequency oscillation phenomena often happen in the process of the power system operation. This paper presents a disturbance resonance mechanism for power system low-frequency oscillation.This paper at first introduces the classic second-order model of negative damping mechanism of power system, and on the basis of it, the resonance mechanism both in the 2nd order generator model and Phillips-Heffron model is derived in detail. It indicates that when the frequency of small low-frequency disturbance signal imposing on the shaft of generating units, regulation system and excitation system is consistent with or close to the power system natural oscillation frequency, the power system will amplify the magnitude of disturbance and transit to the status of low-frequency oscillations in resonance form. Disturbance resonance mechanism is an extension of the resonance mechanism. Disturbances can be found everywhere in power system. LFO in power system will be caused in the case that the sinusoidal component of disturbance signal is closed to system natural frequency. Furthermore, based on disturbance resonance mechanism, we designed both PRBS and sinc function disturbance-signal power sources. According to characteristics of these two signals, we set the frequency of these two sources at the range of 0.1~2.5Hz and calculated their maximum power outputs. We in theory deduced that both two disturbance sources have the feature of small-storage but high-power output. In the end, we applied these two disturbance sources to Single Machine-Infinite Bus System as well as Four-generator two-area System to inspect and verify disturbance resonance mechanism in power system low-frequency oscillations via adding different disturbing capacities and placing diverse disturbing-locations in simulation. We also thought over the influence of lagging effect of the energy storage device at the same time and it provides reference for dynamic simulation experiments in the near future.