Research On Coupling Effect And System Stability Of Train-network-train In Electrified Railway Based On Impedance Analysis

With the rapid development of China’s electrified railways and the large number of AC-DC electric locomotives and EMUs in operation,the interaction between trains and traction networks and between trains that are coupled through the traction network is increasingly apparent.The harmonic interaction between different trains and the traction network may match the characteristic frequency of the impedance of the traction network where the trains are located at a specific frequency,thereby generating train-network coupling resonance.When a large number of trains are put into the traction network at the same time,the phenomenon of low-frequency oscillation also causes people to pay attention to the stability of the system.In the past,the analysis of the train-network system only considered the simplification of single trains or trains at the same location.In actual working conditions,harmonics injected by a train on the traction network may be used as harmonic sources to cause resonance accidents in trains at other locations.The distribution of train position and the parameters of each train also affect the system stability.Therefore,this dissertation analyzes the coupling effect and stability of train-network-train system.The dissertation first analyzes the train-network coupling resonance mechanism based on train harmonic characteristics and traction network impedance characteristics.In addition to the low-order harmonics and the harmonics near the switching frequency,the characteristic harmonics of the medium-frequency caused by the saturated nonlinear characteristics of the converter are analyzed.Based on the discrete system model,the description function method is used to linearly describe the saturated nonlinear links.Through the negative inverse description function of the nonlinear links and the Nyquist curves of other link functions,the system stability and the generation of self-sustained oscillations are analyzed,and the self-sustained oscillations are analyzed.Influencing factors and specific impact on the characteristic harmonics of the intermediate frequency.Simplified modeling of the traction network,focusing on the analysis of the impedance characteristics of the traction network and the corresponding relationship between the impedance characteristics and the resonance voltage of the traction network,a Matlab/simulink simulation model of the traction network based on actual parameters was established,and the resonance mechanism and the traction network were verifiedThe influence of characteristic impedance on resonance provides a theoretical basis for the research of train-network coupling resonance suppression measures.Based on the train-network-train resonance mechanism,in order to suppress the train-network-train coupling resonance,a control method for auxiliary four-quadrant converter based on impedance reshaping is proposed.By detecting the resonance voltage,the auxiliary four-quadrant converter is controlled to generate the corresponding harmonic command,which is equivalent to the harmonic impedance of the corresponding frequency in parallel with a controllable amplitude at the position where the train of the traction network is located.By controlling the amplitude of the equivalent harmonic impedance and reducing the characteristic impedance after parallel connection,the purpose of suppressing resonance is achieved,and the power quality of the system is also improved.At the same time,the factors affecting the suppression effect and the stability of the train after the impedance reshaping control strategy are analyzed.Through the dynamic suppression process analysis,further optimization of the suppression effect.This method can be used when the train itself or other trains on the traction network are used as harmonic sources,and the application range is wider.Through the Matlab/simulink simulation using actual parameters,the suppression effect is verified,and the performance is excellent.Through small signal model and impedance model,this dissertation analyzes the mechanism and influencing factors of low-frequency oscillation of train network system,and analyzes the influence of train parameters and train location distribution on the stability of train network train system when multiple trains with different parameters or at different positions are located.According to the above analysis results,the system stability can be improved by changing the train control parameters and position distribution.To better suppress the low-frequency oscillation of four quadrant converter,an impedance compensation control scheme is proposed in this dissertation.The voltage value of low-frequency oscillation is extracted and fed back to the current loop command.The low-frequency oscillation is suppressed by changing the train impedance to improve the system stability.Through the MATLAB / Simulink simulation with actual parameters,the suppression effect is verified,and the performance is excellent.Finally,an experimental platform is built to verify the correctness of theoretical analysis and the effectiveness of suppression strategies.Simulation and hardware-in-the-loop experiments were carried out on the RT-LAB semi-physical platform,and the effectiveness of the resonance suppression strategy based onimpedance reshaping was verified.A 15 k W vehicle-net-vehicle experiment platform was built to simulate the multi-train and traction network coupling system.The topological structure of the experimental prototype was analyzed in detail and the train-network-train coupling resonance verification was completed using the experimental prototype,and multiple trains low-frequency stability analysis verified the effectiveness of the proposed train-network-train resonance suppression method based on harmonic impedance reshaping and the low frequency oscillation suppression method based on impedance compensation.Figures: 104.Tables: 13.References: 152.