Study On Mechanism And Control Measurement Of Low Frequency Oscillation In Interregional Power Grid

The successful implementation of network interconnection has tremendous economic and social significance. The large-scale optimized distribution is made possible and the economy and reliability of systematic power generation and transmission is improved by the interconnection. However, a lot of dynamic stable problems are caused by the interconnection. The most possible one is the low frequency oscillation. Its occurrence in power network in China and abroad seriously endangers the stable operation and high attention of power enterprises and academic circle is attracted. With the unremitting efforts of electric power professionals, a series of research results have been achieved, but there are still many problems remain unsolved. How to interpret and solve the problem of low frequency oscillation well seems crucial in the network interconnection today. Its cause, mechanism, feature extraction and inhibition are all problems waiting for solving.Plenty of relative sources are referred, analyzed and concluded in this paper. Based on the work done before, the deep and systematic research has been done from the aspects of cause, mechanism, the method of modal identification, inhibition, comprehensive precaution and intelligent control strategy, and relevant results are achieved. The paper mainly researches in the following aspects:Detailed theoretical analysis of non-linear singular mechanism and chaotic mechanism of low frequency oscillation are implemented, and simulation and verification is also made. Resonant transmission mechanism is established, the effectiveness of the mechanism verified by using grid structure parameters of systems in North America and China.An interface power flow analysis model which could maintain the dynamic feature of the generator is established and the transient energy function calculation is simplified. Based on the model, the method of transient energy function is applied to the mechanism analysis of the multiple disturbances in low-frequency oscillation, using the concept of critical energy to explain the phenomenon of multiple disturbances in low frequency oscillation. The multiple disturbance is the one which happens orderly in time, firstly a small disturbance, then sometimes a small disturbance, and sometimes a series of secure strategies for the small disturbance. And the secure strategies which are involving are the very disturbance to the system. The low frequency oscillation which is caused by multiple disturbances happens sometimes after the transient stable phenomenon; therefore the principle of transient energy function could be used to analyze the mechanism of multiple disturbances. Analyzing the low frequency oscillation of the power system from the energetic aspect could get some significant guiding strategies in the inhibition of low frequency oscillation, insurance of systematic stability and etc.The method of modal identification and extraction of the needed modal information from practical oscillation signals by data mining of low frequency oscillation signals based on the measured data is researched. Firstly, the ITD method which used to be applied on mechanical free oscillation and ARMA method which used to be applied on digital signal process in the modal identification of low frequency oscillation in Interregional power system is adopted and simulation and verification is established. Then the method of matrix pencil fuzzy identification is mainly studied, and the method of basic matrix pencil based on the method of order selection by analyzing principle components and singular entropy is established.Whether in the noise-free or in the noise situation, the modal order could be determined quickly, automatically rejecting false modal and undermining the calculating complexity. The effectiveness and feasibility of identifying the wide area systematic low frequency oscillation signals based on the matrix pencil method of order selection singular entropy analysis is verified by the simulating results.The inhibiting strategies of low frequency oscillation are discussed, considering the excitation system of generator is of great importance to enhance the systematic stability, and is the simplest, the most economic and efficient strategy among the ones which could improve the stability of power system, having a significant practical meaning in accelerating the research and industrial practice of excitation control theory. Based on the comparison and analysis of some frequent excitation control algorithm, the uncertain non-linear system Terminal sliding mode variable structured excitation control algorithm is established, its designing principle and process are carefully derived and the stability is analyzed. The outstanding advantage of this controller is mollifying the transient process in the limited time. Implementing the model of excitation controller in the PSASP environment, the significant effect of this algorithm in inhibiting systematic low frequency oscillation is verified by the simulating experiments and the stability is improved. Referring to the features of ultra-high voltage grid, the low frequency oscillation quick early-warning index algorithm based on multiple disturbance and intelligent control strategies is established; the dynamic coherency identification method is deeply researched and realized. Safe early-warning system of the wide area power network low frequency oscillation is designed and the structure of early-warning platform is established, providing the effective protection for the safe operation of power network.