Study On Chaotic Dynamic Behavior And Control In Power System

Chaos theory is an important aspect of non-linear research, and has infiltrated a number of disciplines and engineering fields. With the increasing scale of power systems, the nonlinear characteristics are more and more obvious, under certain conditions there will even be chaotic behavior, appears as irregular electromechanical oscillations, constituting a threat to the system. The thesis concentrates on chaos theory in power system applications. The specific purpose of the study: To explore behavior characteristics of the chaotic dynamics in the power system, to study inception mechanism of chaos, chaotic detection in power system and effective measures to elimination of chaotic oscillation in power system. The Thesis includes following sections:(1) The thesis analyzes nonlinear dynamic behavior of power system and its operation characteristics of chaos. Power system is a typical nonlinear dynamic system; chaos is a unique and special operation in nonlinear dynamic system. Analysis of chaotic behavior for Power system is the scope of nonlinear dynamic analysis. Nonlinear dynamical systems theory and methods are used in the thesis, especially with the use of the phase diagram and the poincar section method, bifurcation theory, lyapunov exponent method and correlation dimension method. Through drawing phase diagram and calculating state characteristic parameters of the system, the running behavior (including the phenomenon of chaos) of the operating system is determined. With the use of non-linear power system model and numerical calculation based on the Runge-Kutta method, simulation figure is drawled and eigen value is calculated. Analysis and simulation results show that the power system under nonlinear model with different control parameters, shows complex dynamic behavior, even will produce chaotic oscillations under certain conditions.(2) The thesis detects chaos in power system. Through numerical analysis of nonlinear power system model, and observing of the phase diagram, timing diagram, divergence and convergence of adjacent tracks, as well as the quantitative calculation of the maximum Lyapunov exponent, correlation dimension and the measure of entropy, the Thesis judges and detects chaotic in system. However, the actual power system, are often unable to obtain accurate models can only obtain one or some of the time series of state variables. The thesis in the above analysis, detects chaotic phenomena of power system based on nonlinear time series analysis method. In this process, mainly the non-linear time series phase space reconstruction method is deployed. Embedding dimension and delay time are determined by G-P method based on Taken theorem and auto-correlation function method. MATLAB simulation tools are used for validation and experimentation, to map out the phase diagram based on a specific state of the power system time-series. The simulation results show that reconstruction of the phase diagram is with the characteristics of chaos, and can to detect the phenomenon of chaos using non-linear time series analysis method, and measured value of state variables (i.e. time series) of power system.(3) The thesis takes effective control measures to curb or eliminate the chaotic oscillations in the non-linear power system. Chaos oscillation in the power system is harmful and should take measures to suppress and eliminate. There have been a lot of chaos control methods, and each has its own advantages and disadvantages and different application conditions. Chapterâ…£in the thesis using differential geometry method, designs nonlinear power system controllers and systems asymptotic tracking output controller to eliminate the chaotic oscillations. The basic idea of the method is: take a diffeomorphism mapping and coordinate transformation to the nonlinear model, to get exact linearization model of the power system, with the state feedback. At last, optimal control method is adopted to design the chaos controller of the power system. Asymptotic tracking output controller is designed on this basis, by adjusting the control rate. The theoretical analysis and simulation results show that, based on the differential geometry of the chaotic controller not only can eliminate the chaotic oscillation, but also be able to control the system to any given orbit, the effect was better than the traditional method of linear approximation.Chapterâ…¤in the thesis designs asymptotic tracking output controller of the chaos power systems using sliding mode control method. The main drawback of sliding mode variable structure is that there will be high-frequency chattering. The thesis improved the algorithm, improvement 1: Dynamic switching function and the quasi-sliding mode control method of combining are designed to eliminate the high-frequency chattering ; improvement 2: Fuzzy control rules are introduced in the sliding mode variable structure controller design and isokinetic convergence rate is replaced by exponential convergence rate to eliminate the high-frequency chattering. The theoretical analysis and numerical simulation results show that two methods based on the above sliding mode controllers can eliminate the chaotic oscillation, make the system track with a given signal, effectively eliminate the high-frequency chattering appearing in the sliding mode, and can improve the tracking speed, control effect is better than conventional sliding mode controller.