The Inhibition Methods Of Low-frequency Oscillation In Vehicle-grid System In Electric Railways

In recent years, there have been many low-frequency oscillation accidents of electric locomotives appeared in our country, severe oscillations lead to the abnormal operation of electric locomotives with the cause of traction blockade, which seriously affected the normal order of railway transportation. Base on the low-frequency oscillation phenomenon of electrified railway, this paper analysis the influence of control algorithm of ac-side converter in traction drive system for low-frequency oscillations, and give two suppression methods of low-frequency oscillations, then reproduces the low-frequency oscillations in the simulation in time domain. This provides theories and models for engineers to solve the low-frequency oscillations and has important engineering significance.Firstly, according to the low-frequency oscillation phenomenon in our country, mathematical model of the traction power supply system (including traction and traction transformer)is given, as a case study of CRH3 electric rail vehicles, inverter and traction motor models are reasonable simplified, a vehicle-grid model is designed.Secondly, in order to study the mechanism of electrified railway low-frequency oscillation, it can obtain the key factors which influence the stability of the vehicle-grid system, this dissertation establish a small signal "input-output" model of the vehicle-grid system from the mechanism and transient direct current control strategy of the line-side converters, use damping coefficient to analysis the PI controller parameters of the control strategy to the low-frequency oscillations.It provides an important reference basis to the methods of restrain the low-frequency oscillations by optimizing the PI controller parameters.For further suppress low frequency oscillation phenomena occur, draw lessons from modern control theory, the line-side converter control strategy of multivariable pole-placement control has been designed. By analyzing the stability of vehicle-grid system which controlled by multivariable pole-placement control, it provides this control strategy has better ability of low frequency oscillation suppression contrast with the instant current control strategy.In order to verify the correctness of the theoretical research, this paper set up a vehicle-grid model in the time domain simulation. Combined with the low-frequency oscillation criterion and referenced to low-frequency oscillation field test waveform, it successfully reproduced the low-frequency oscillation phenomenon. On this basis, the optimization of PI parameters of low frequency oscillation suppression method was verified and low frequency oscillation criterion was verified at the same time. Simulation verifies the multivariable pole-placement control strategy has a reliability effect of the converter control and the ability of low frequency oscillation suppression.Finally, based on DSP TMS320F28335 controller, and RT-LAB experimental platform, the low-frequency oscillation phenomena and oscillation suppression method is verified, and the validity of the vehicle-grid model and the effectiveness of the low frequency oscillation suppression methods are verified by the experiment results.