Analysis And Control Of Low Frequency Oscillations In Interconnected Power Systems

Low frequency oscillations among interconnected synchronous generators are phenomena inherent to power systems. The stability of these oscillations is of vital concern, and is a prerequisite for secure operation of power system. Due to large scale and complexity, conventional small signal stability analysis cannot meet the demand of plan, design and operation of the power grid. According to these situations, this dissertation brings forward an integrated analysis method and control strategy in oscillation research, which can be applied to prompt the level of dynamic stability analysis and provide the solution for real system. The main research work is summarized as follows:As the basis, the concept and process of eigenvalue analysis are discussed first. Then according to the research of the state matrix, a concept that the system general damping coefficient keeps constant is proposed, which is helpful for understanding the interaction of all the dynamic components and impacts for the distribution of dampings. Some fundamentally influential factors such as systemic structure, the distribution of power flow, effects of excitation system and PSS, as well as characteristics of load models, etc, are discussed in detail to study the systemic damping. Digital simulations reveal many valuable characteristics of the power system low frequency oscillation.The limit of conventional analysis and the appearance of new technique such as WAMS together with the advance of the nonlinear theory, require a new method for oscillation research of power grid, which can combine small and large disturbances analysis effectively.Measurement based dynamic system identification method is presented in the paper. Firstly, a new iterative version of Prony analysis is proposed, which has better performance than the conventional one. Then the pattern recognition of power grid's transient response and identification of reduced order linear model using Prony method are discussed in detail.A powerful tool of dynamical system analysis named normal form method is presented in this dissertation, and then it was used to analyze oscillation phenomena in interconnected power grids. Using nonlinear coordinate transformation of normal forms, a fully described power system can be converted to an equivalent reduced order model, which can still use the conventional modal analysis of small signal stability problems. Applying normal form method, conventional eigenvalue calculation and Prony analysis, small signal stability and time domain simulation can be combined efficiently. Theproposed method can get nonlinear information which never obtained by past techniques, so it shows a new way for analyze oscillation problems in interconnected power systems.China power industry has been stepping into the stage of nation-wide interconnection. With the increasing demands for security, stability, and economy, the requirement on the level of power system analysis and control is also enhanced. Some intelligent analysis methods and control strategies are studied in the dissertation, among them, data mining based small signal stability assessment and genetic algorithm based multiple PSSs design are described in detail.With high practicability, a set of novel analysis methods and control strategies on low frequency oscillations in interconnected power grids is established by the research results of this dissertation.