Study On Nonlinear Dynamics Of Ferroresonance Overvoltage And Its Chaotic Synchronizing Suppression

With the rapid development of domestic economics, the power grids in China become more extensive and complicated. Ferroresonance is a nonlinear dynamic electrical phenomenon, which frequently occurs in power systems. Ferroresonance overvoltage can cause severe damage to power systems because of its high magnitude and long time. Nowadays, modern grid demands continuous online real-time monitoring in order to detect existed or developing faults. Thus, the appropriate measures should be taken to make sure the reliability, safety, quality and efficiency of power grids. So the automatic suppression of ferroresonance in early stage is of great importance to realize the"self-heal"function in intelligent grid.At present, the research on the suppression of ferroresonance in grounded system is relatively less, particularly compared to that in un-grounded systems. The main reasons cause the nonlinear characteristics of power systems is the saturation of potential transformers and no-loaded power transformer. In this thesis, the nonlinear characteristics of the nonlinear element such as the iron core and metal-oxide arresters (MOA) are studied at first. According to the principle of ferroresonance in grounded systems, the mathematical model is constructed by normalizing the system parameters. Thus, the differential equations of ferroresonance circuit can be obtained. So the nonlinear dynamics of ferroresonance can be studied by applying the mathematical methods such as phase map, Poincare map, power spectrum, Lyapunov exponents and bifurcation map, which is the base of further research.Because MOA is another important nonlinear element which affects the nonlinear characteristics of ferroresonance, the nonlinear dynamics of ferroresonance system with metal oxygen arresters (MOA) are studied for the first time in this thesis. The effects of MOA on ferroresonance overvoltage, especially its chaotic characteristics, of neural grounded systems are analyzed. The results show the ferroresonance overvoltage can be clamped and the chaotic ferroresonance can be transferred to non-chaotic one by installing MOA. And the range of parameter values for which chaos persists and the sensibility of systems to initial values are reduced. In addition, V-I characteristics is improved based on the anaylysis which can suppress overvoltage more. This is valuable to engineering application.A new concept of suppressing ferroresonance was proposed after analyzing the nonlinear dynamics and characteristics of ferroresonance. In this concept, a method of feedback impulsive chaotic synchronization was utilized to synchronize the ferroresonance system with normal system. The feedback coefficients can be obtained by the stability theorem. The quickness and energy-efficiency of this method was proved by simulation in MATLAB, which was also proved by ATP-EMTP for the first time. In addition, this method is also useful to the non-chaotic systems which have never been studied before.Overall, the effects of MOA on the nonlinear dynamics of ferroresonance are studied. The feedback impulsive controller is designed as well. This research makes up the incomplete research on ferroresonance of grounded systems.