Research On Stability And Suppression Measures Of Low Frequency Oscillation Of Electrified Railway

In recent years,the frequent occurrence of low-frequency oscillations in railway hubs in China has seriously affected the normal operation of trains and traction power supply systems,and endangered the safety of related power equipment.In response to the above problems,this paper takes CRH5 electric multiple unit as the object,analyzes the stability of electrified railways,and proposes an improved forbidden region criterion.On this basis,an active disturbance rejection controller optimized STATCOM device scheme is designed to suppress the low-frequency oscillation of the traction power supply system from the grid side.And through the particle swarm algorithm and the improved forbidden region criterion,the control parameters of the scheme are optimized.First,the topology and functions of the train-network coupling system are studied.The impedance method is used to calculate the total impedance of the traction power supply system,and the small-signal impedance model of the traction network side is established according to the results;the CRH5 electric multiple unit model is mathematically analyzed,and the small-signal admittance model of the train is established,which provides the basis to the theoretical analysis of the stability of the network coupling system.Then,a time-domain simulation model of the train-network coupling system was built based on Matlab/Simulink,and the phenomenon of railway low-frequency oscillation was reproduced as a verification method for the theoretical research in this paper.Secondly,in order to focus on solving the conservative problem of the stability analysis of the train-network coupling system,according to the Nyquist criterion,the forbidden region of the criterion is reduced,and an improved forbidden region criterion is proposed in combination with the Gaelic circle theorem and the variant of the return ratio matrix.This criterion has the advantages of low conservativeness and quick judgment of system stability,and can be used for stability judgment based on the port measurement impedance matrix.By comparing the established small signal model with the stability identification results of different criteria,the reliability and advancement of the proposed criteria are verified.Then,in order to suppress the railway low-frequency oscillation phenomenon,an oscillation suppression scheme based on active disturbance rejection controller and STATCOM device is designed to suppress the oscillation.Aiming at the insufficiency of disturbance immunity and smoothness of the PID controller in the converter control of the STATCOM device,an active disturbance rejection controller is used to replace the PI link in the voltage outer loop,which improves the stability and robustness of the system.The improvement effect of the device on the stability of the train-network coupling system is analyzed by the improved forbidden region criterion and simulation model.Finally,the particle swarm algorithm and the improved forbidden region criterion are used to optimize the control parameters in the STATCOM device and improve the effect of oscillation suppression.Using the improved forbidden region criterion as the objective function of the particle swarm algorithm,combined with the small signal model of the train-network coupling system based on the STATCOM device,two sets of optimized control parameters are obtained through the algorithm;the coupling system of the two sets of parameter values is compared by the improved forbidden region criterion curve,The final STATCOM optimized control parameters were obtained.The simulation verified that the optimized parameters have improved the suppression effect of the STATCOM device.