Research On Neutral Point Voltage Of EMU Three-level Traction Converter

Nowadays rail transport system in China plays a key important role, and Harmony CRHEMU emergence of a key role in promoting China’s railway development. The tractionconverter is a part of EMU traction, which plays an impotent role in EMU’s key technologysystem. The structure consists of an AC-DC-AC converter system by traction rectifier, DClink and the traction inverter.The three-level traction converter was studied in this paper, analysis of its workingprinciple and control methods. At the same times, a system of mathematical models wasestablished. A mathematical model of single-phase three-level rectifier and three-level NPCinverter were set up. In this paper, analyze the causes and impact by the reason of the DC busvoltage imbalance, and set up the neutral point current’s mathematical model, and reduced thecapacitor voltage unbalance. And it presented several of software control methods to reducethe imbalance in the mid-point potential.At the end of this paper, with the application of MATLAB/AIMULINK software, it hasestablished the three-level traction converter system simulation model. Respectively forsingle-phase three-level rectifier and three-level NPC inverter for a simulation study, thesimulation results obtained to verify the correctness of the converter control. After Simulationand experimental, the neutral voltage maintain a certain degree of balance by different controlmethods, so that verify the correctness of control and the system.