Modeling and Evaluation of Common-Mode EMI Coupling Through Converter Chassis in Metro Traction System

The internal layout of the converter chassis in metro traction system is compact, and the electromagnetic couplings among power circuit, control circuit, and converter chassis are complicated. The electromagnetic interference (EMI) generated by the high-speed switching of power devices couples to the control circuit through the converter chassis, which may affect the safety and reliability of the system. In order to evaluate EMI performance at low-voltage power ports effectively, this article studies noise coupling mechanism on how common-mode (CM) EMI from the power circuit propagates to the low-voltage power cables through converter chassis. A multiterminal impedance network model of the converter chassis with an impedance matrix is built, and the parameters in the impedance matrix are extracted. The high-frequency models of coupling impedances between the converter chassis and different components are built, and the parameters of coupling impedances in the models are extracted. Based on these works, an estimation model of CM EMI coupling from power circuit to low-voltage power port through converter chassis is proposed. With the proposed model, the CM EMI at low-voltage power port is simulated. Different grounding schemes of the converter chassis are evaluated, and the optimal grounding position on the converter chassis is found. The simulated results are verified by experiment.