The Mechanism And Suppression Technology Of Overvoltage During Passing Neutral Section Of CR400AF EMU

In recent years,China’s high-speed railways have developed rapidly.CR400 AF EMUs have been put into operation in large numbers,with operating speeds up to 400km/h.At present,due to the overvoltage damage of some electrical equipment such as on-board voltage transformers,on-board electrical connectors,and line voltage transformers during passing neutral section of high-speed EMUs,which affects the safety of its operation,so it is necessary to carry out research on the mechanism and suppression strategy of overvoltage generated during CR400 AF EMU’s passing neutral section.Firstly,a mathematical model of CR400 AF EMUs passing neutral section was established.Based on the complete electrical phase separation section of the traction power supply system,a model including traction substations,traction networks,AT stations,sub-regions,and electrical phase separation was established.At the same time,the RL impedance model when CR400 AF EMU is traveling in the non-electric phase separation section and the LC parallel equivalent model when the CR400 AF EMU is traveling in the electrical phase separation section are established.Secondly,the mechanism of overvoltage during passing neutral section of CR400 AF EMU was analyzed.The process of passing neutral section was divided into 6 stages,and the state space equation method was used for theoretical analysis of each stage,and then the mathematical model of each stage was simulated and analyzed based on MATLAB/Simulink software.The simulation results show that the most serious overvoltage of CR400 AF EMU passing neutral section generates at the stage one,that is,the circuit breaker disconnection stage,and the overvoltage is closely related to the current at the time the circuit breaker is opened,and the overvoltage value is the smallest at the current zero-crossing point,the overvoltage value is the largest at the peak of the current,the amplitude can reach 92 kV,which is about 3.3 times of the rated voltage of the catenary;the faster speed of the CR400 AF EMU passing neutral section,the greater of the load power,the more serious the overvoltage.The overvoltage value of each stage accords with the result of the theoretical calculation,which proves the correctness of the mechanism analysis.Then,aiming at the stage of the most serious overvoltage of CR400 AF EMUs passing neutral section,that is,the CR400 AF EMU breaker disconnection stage,four suppression strategies to reduce the overvoltage are proposed,namely,load reduction during passing neutral section,speed reduction during passing neutral section,power electronic switch to replace circuit breaker during passing neutral section,and power electronic switch to assist circuit breaker during passing neutral section.The theoretical analysis shows that the four methods can reduce the overvoltage of CR400 AF EMUs passing neutral section.Finally,based on MATLAB/Simulink software,the four overvoltage suppression strategies were simulated and analyzed.The simulation results showed that the overvoltage was reduced to45 kV by load reduction during passing neutral section,which was about 1.63 times of the rated voltage of the catenary;the over-voltage was reduced to 58.48 kV by speed reduction during passing neutral section,which was about 2.1 times of the rated voltage of the catenary;the overvoltage was reduced to 39.31 kV by the use of power electronic switch suppression strategy,which was about 1.45 times of the rated voltage of the catenary.The result proves the correctness of the research on the mechanism and suppression strategy of overvoltage generated during CR400 AF EMU’s passing neutral section.Comprehensive comparison,the strategy of the power electronic switch to replace circuit breaker during passing neutral section and power electronic switch to assist circuit breaker during passing neutral section both have obvious effect on reducing overvoltage in the aspect of theory and simulation.As the power electronic switches may experience breakdowns,failures,etc.,the strategy of power electronic switch to replace circuit breaker during passing neutral section exists risks.Therefore,the strategy of the power electronic switch to assist circuit breaker during passing neutral section can be used as a transitional solution to reduce the overvoltage of the EMU,and it can provide a reference for the future application of power electronic switches to replace the circuit breaker during passing neutral section.