Analysis And Suppression Of Electrical Oscillation Mechanism Of High Speed Railway Train-grid System

In recent years,low-frequency oscillation(LFO)phenomenon frequently occurs in the EMUs traction network coupling system(ETNCS)in the high speed railway.LFO is the synchronous oscillation of grid voltage,grid current and rectifiers DC-link voltage in the grid-side,which seriously affects the stable operation of the ETNCS and the transportation order of the railway system.In order to analyze and suppress the LFO,this paper takes the CRH5 in the ETNCS as an example.Aiming to improve the stability of the ETNCS,the impedance analysis of multi-input multi-output system is adopted to study the mechanism and suppression of LFO in the ETNCS.Firstly,the structure and principle of the ETNCS are studied to establish the system model,which lays a theoretical foundation for stability analysis.As for the traction network,the equivalent impedance model is established according to the transformer and transmission lines impedance.For the EMU,combined with the voltage and current decoupling control in the dq coordinate,the small-signal modeling of the single-phase pulse rectifier in the grid side is carried out to obtain the equivalent impedance model of CRH5.The time domain simulation of the ETNCS is built based on MATLAB/Simulink,which verified the correctness of the system modeling method.Moreover,in order to analyze the mechanism of LFO,an improved forbidden region-based criterion(IFRC)is proposed.The stability of the ETNCS is analyzed and compared with the time domain simulation,which verifies the accuracy of the proposed criterion.Further,the development of IFRC shows the influence of ENTCS electrical parameters and the control parameters on the system stability.Therefore,the mechanism of LFO is revealed,which lays the theoretical foundation for the suppression of LFO.Through the joint simulation of the ETNCS and the hardware-in-the-loop(HIL)test,it further proves that the proposed criterion has less conservativeness.In addition,in order to study the suppression of LFO,three controllers are designed.Aiming at the nonlinear characteristics of the grid-side rectifier,a nonlinear PI(NPI)controller is designed,combing with the traditional PI controller and nonlinear function,to realize the adaptive adjustment of the control parameters.The tracking differentiator is introduced to avoid the overcurrent problem caused by large error during the start-up period,which constitutes the auto disturbance rejection error(ADRE)PI controller in the voltage control loop with complex structure and parameters identificantion.In order to simplify the control structure,the controllers of the rectifier voltage and current are designed based on the linear active disturbance rejection control(LADRC),whose controller parameters are set by the Nyquist criterion.Furthermore,in order to analyze the dynamic and static performance of the above controllers,mutation tests of load and voltage are carried out in simulation.The simulation result infers that all three controllers can achieve stable control of the system.However,the adjustment time of the NPI controller is long,and the anti-interference of ADRE controller is poor.While LADRC has the comprehensive optimal performance in anti-interference and dynamic response.Besides,the time domain simulations of the ETNCS adopting the above three controllers are built respectively to compare and analyze the static performance of the above controllers.The simulation result indicates that the above three controllers can significantly improve the stability of the ETNCS,which verifies the effectiveness of the design schemes for the LFO suppression in the ETNCS.