Analysis And Control Of Low-Frequency Electromechanical Oscillations In Power Systems Based On Prony's Method

This thesis focuses on analysis and control of low-frequency electromechanical oscillations in power systems based on Prony's method. The main work is as follows:1. Chapter 1 presents the classification, causes, and harmful subsequences of low-frequency electromechanical oscillations in power systems. Some typical accidents resulting from this kind of oscillations are presented. A comparison of deferent kind of measures to damp electromechanical oscillations is made. And an introduction to some software packages for analyzing electromechanical oscillation, including PSS/E, Matlab and SSAT, is made at the end of this chapter.2. Chapter 2 discusses the inherent drawbacks of eigenanalysis and presents Prony's method. The principles, useful indexes and parameter selection of Prony's method are discussed in detail. Then the tests on selection of parameters such as sampling frequency, time interval and model order are made and their impact on the result of Prony analysis is analyzed. Prony's method is then extended to analyze multi-output signal. The impact of nonlinearity on Prony's method is discussed as well. Prony's method is used in transfer function identification, and it is useful for controller design for damping electromechanical oscillations.3. Chapter 3 discuses the selection of damping controllers, especially for PSS, HVDC small signal modulation and TCSC modulation. Then residues associated with the oscillation of interest are used as the effective index and their relative magnitude under several operation conditions are used as the robust index of damping controllers. The design procedure of damping controllers is presented, including PSS, HVDC small signal modulation and TCSC modulation. Prony's method is used in open-loop transfer function identification and computation of residues. The pole-placement method is used in the design of controllers. The 4-machine system example validates the effectiveness of this Prony's method based damping controller design.4. Chapter 4 presents a detailed analysis of low frequency inter-area oscillations of the South China Interconnected Power System for the year of 2005 based on the eigenvalue analysis method. Participation factors and mode shape diagrams of generators related to the inter-area oscillations are figured out, and locations of PSS are determined accordingly, the parameter setting for the PSS is studied as well. The method of HVDC small signal modulation is applied to enhance the small signal stability of the system; the results are investigated based on the Prony method. Theinfluences of components outage in the transmission corridor on the inter-area oscillations are further investigated, and some important conclusions are drawn.