Research On Resonance Mechanism Of Power System Low Frequency Oscillations

On the basis of analyzing the traditional mechanism of low frequency oscillation in power system, the paper establishes the resonance mechanism theory system with concepts, formula, oscillating characteristics and rising factors. Applying this theory, an unknown mechanism oscillation field case is successfully studied. The main studying achievements are shown as follows: 1. The paper presents the resonance mechanism for power system low frequency oscillation for the first time. A single machine to infinite system expression is deduced. And for generator Phillips-Heffron model, the resonance mechanism is analyzed. The oscillation characteristics and rising factors are totally discussed then. It is pointed that the disturbance on turbine shafting, speed governor system and excitation system can all cause the resonance oscillation. This mechanism expanded the low frequency oscillation mechanism, and can be successfully used to explain some unknown reason field case. 2. The paper presents an experimental method for analyzing the low frequency oscillation, which focus on the field data and the simulation validity. This method is in accord with the physics rule, which suits for new mechanism studying and existing theory validity testing in power system. 3. An improved Prony method is presented in this paper, which suits for kinds of noise and disturbance. The method can be used to analyzing the field data, which providing a handful tool for power system dynamic analyzing. 4. An application of resonance mechanism for low frequency oscillation is that successfully explain the unknown mechanism An-Bao line oscillations in Hebei south grid. The oscillation characteristics of An-Bao case are obtained by the improved Prony method. And a series of resonance mechanism simulation are carried out to reproduce the An-Bao line oscillation. The simulation results fit the field data quite well, which shows the resonance mechanism is the proper reason for An-Bao line oscillations. 5. After discussing the measured impedance trace during oscillations by field data, a new startup criterion is discussed for low frequency oscillation recording. 6. Some problems in dynamic data recording are summarized in the last part of the paper. Solving such problems are depending on not only device manufacturers but also operating units. The achievements of this paper enrich the low frequency oscillation theory, and providing a new idea for field case studying. The theoretical work of this paper establishes one of the fundamental works for machine-grid correspond control research.