Research on DC Bus Voltage Resonance Mechanism for Metro Power Supply System

The operational safety of metro systems depends on the stability and reliability of their power supply systems. With the continuously increased traffic density and the massive grid connection of new energy systems, metro power supply systems suffer from frequent significant changes in electrical characteristics, such as special loads similar to short circuits potentially occurring on the traction side, and DC bus resonance. This paper aims to response to the problem of nonlinear oscillations in bus voltage. A mathematical model of the third-order nonlinear nonautonomous equation of state was established for the rectifier transformer circuit at the AC side. By adding a time dimension, the third-order nonautonomous system was transformed into a fourth-order autonomous system, and numerical analysis was conducted to examine the three-dimensional phase diagrams, phase plane diagrams, Poincare mapping diagrams, and bifurcation diagrams of the system. The chaotic waveforms obtained from simulations were compared with the oscillation voltage waveforms measured on site after 24-pulse rectification. The comparative analysis results showed that the simulated waveforms basically aligned with the recorded waveforms in terms of amplitude and frequency, proving that the occurrence of significant fluctuations in power grids contributes to nonlinear oscillations in the traction power supply system of metro systems.