Research On The Effects Of Geomagnetic Storms On Voltage Transformer Of EMUs Based On Chaos Theory

With the rapid development of economy and society in China,the high speed EMU is the development trend of modern railway.The high-speed railway become more extensive and complicated.Geomagnetic storm,a massive scale and sudden disaster space weather,has been reported that it poses a threat to the safe operation of the railway system.So far,due to the research on the effects of geomagnetic storms on railway system is in the initial stage,the main methods are traditional linear system analysis,which can not be an accurately method for some nonlinear phenomena.This paper based on the nonlinear theory,studies chaos phenomena of EMUs’ voltage transformer with the method of chaos analysis in high speed railway traction power supply system,accordingly having some prospect and innovation.In this paper,which based on nonlinear theory,nonlinear and excitation current are combined accordingly to voltage transformer magnetization characteristic when GIC is affecting it.This paper establishes the GIC circuit model with voltage transfoemer,which was analyzed to study the possibility of voltage chaotic oscillation in voltage transformer based on the chaos theory.The Melnikov function method is used to get the quantitative conditions for the chaos of the voltage transformer under different parameters.By bifurcation diagram and Lyapunov exponent,the nonlinear characteristics totality of voltage transformer under different excitation and the influence of different magnetic characteristics on chaos phenomena is studied,so as to determine the parameter range of the voltage chaotic oscillation.By the phase diagram,the voltage waveform,the Poincare surface of section and the three dimensional graph,the three nonlinear forms of voltage ’stability’,’chaos’ and ’transition’ are studied in voltage transformer.According to the voltage transformer core loss resistance is easily affected by GIC,through simulation this paper analyzed the effects of linear and nonlinear iron core loss resistance on the chaotic characteristics of voltage transformer.Through comparative analysis,the study shows that the nonlinear core loss resistance can be equivalently instead of linear core loss resistance.The simulation results show that if the position of the EMUs in the AT power supply area is different,the voltage chaotic oscillation of the voltage transformer is not the same.Tracking controller and feedback pulse controller are designed to suppress chaos phenomena in the voltage transformer caused by geomagnetic storm.Through using the system operating at rated voltage as reference,the control signal is added in the chaotic system.Then the chaotic system is synchronized to the reference system to realize the synchronization of the chaotic oscillation voltage and the normal operating voltage,so as to suppress the chaotic oscillation of the voltage.Simulation results shows the effectiveness of the controller.