Research On Leakage Current Mechanism And Test Of EMU Coupling

With the continuous increase in the mileage and speed of high-speed EMU in recent years,a higher requirement for the safety performance has been proposed.Electrical corrosion faults caused by motor leakage current of EMU have gradually increased,and to solve the problem of motor leakage current is becoming more and more important.At present,the leakage current mechanism through the EMU coupling is unclear,the coupling leakage current composition during the operation of EMU also needs to be researched.In respect of the issues above,The motor leakage current model is established based on the transmission structure relationship of EMU,and the equivalent circuit model of the motor leakage current was established based on the equivalent impedance relationship of the transmission structure which include motor,coupling,gearbox and so on.Then,the transfer function and frequency response of equivalent circuit model are analyzed.Furthermore,the mechanical structure characteristic of the coupling is analyzed,and the mathematical model of the coupling tooth surface is established by using coordinate transformation method.Then,the relationship between the coupling shrinkage resistance and the operation condition which is calculated by characteristic of the coupling operation.Finally,The data acquisition of EMU motor leakage current through the full-scale train test,which is applied to identify the parameters of the equivalent circuit model,and to verify the deviation.The main research contents in this thesis include:1.According to the structural characteristics of the motor leakage current model,the relationship between the equivalent impedance and the motor torque and speed is analyzed and is applied to establish an equivalent circuit model.The transfer function of the equivalent circuit model is derived,in which the input is three-phase common mode current and the output is coupling leakage current.Then,based on the characteristics of the three-phase common-mode current input,the frequency response of the leakage current system of the motor is derived.2.According to the machining principle of the drum-shaped gear coupling of EMU,the mathematical model of the tooth surface of the coupling is established.The contact area and shrinkage resistance of the drum-shaped gear coupling under different torques of the motor are derived.Then,the correlation function is derived which between coupling contact resistance and torque.The contact resistance of the coupling decreases as the inclination angle when the shafts increases,and decreases as the torque increases.3.According to current sensor mechanism,the mechanical structure of the current sensors and the installation method of the acquisition device and the test scheme are designed.Sensors are installed in the corresponding parts of EMU,and the leakage current data of the motor during the operation of EMU are obtained.In the factual operation,the peak value of the common mode current of the motor reaches 20 A,and the peak value of the coupling leakage current reaches 900 m A.4.The time domain characteristics of the current data is analyzed.Then,the current data is intercepted according to the output torque of the motor,and using Fourier transform to obtain its frequency domain characteristics.And the least squares standard matrix is constructed base on the relationship between the system output-input amplitude ratio and frequency.Making use of the least square method to fit the frequency response curve and obtain the system parameters,the result shows that the coefficient of determination between the fitting curve and the actual leakage current signal is 71.82%,therefore,the fitting curve can effectively express the actual leakage current signal.Based on the fitted system model,The motor coupling leakage current is predicted by three-phase common mode current data from other operating conditions.And the accuracy of the predicted current is judged by the scale-root-mean-square-error,which result between the actual coupling leakage current and the predicted coupling leakage current is 21.28%.It shows that the prediction system can predict the actual coupling leakage current changing trend effectively.