Mechanism Analysis And Suppression Of Harmonic Instability Of Vehicle-Network Coupling System In Electrified High Speed Railway

As the proportion of electrified high-speed railways in the transportation system is increasing year by year,this has contributed to an irreplaceable role in accelerating the construction of a carbon-free power network system.The controllability of the vehicle-network coupling system and the quality of energy transmission have been fully embodied due to the power electronic conversion function of the converter connected to the traction power supply network in a high proportion.However,this also increases the risk of interaction instability of the vehicle-network coupling system.For a long time,researchers have focused on the study of low-frequency oscillation faults of interactive instability,but there are few research literatures considering the phenomenon of resonance instability.This hinders its long-term and stable operation guarantee in complex actual conditions,and the resulting failures and losses limit the further development of electrified high-speed railways.Therefore,the content of this article is to study the mechanism and suppression strategy of resonance instability of the electrified high-speed railway vehicle-network coupling system.Firstly,the basic theory of the necessary harmonic transfer function method is explained,and then the structure and function of the traction power supply network system,high-speed train and vehicle-network coupling system are briefly introduced.Considering that the existing literature on the impedance model of the car-side converter lacks the ability to be applied in the high frequency range,by fully considering the frequency coupling characteristics in the actual converter and the characteristics of the nonlinear link in the controller,using the linear period time-varying theoretical framework,the topological structure of the high-speed railway traction power supply network and electric drive locomotives are accurately modeled in harmonic domain impedance.It also compares and analyzes the influence of the non-linear link,that is,the analog-digital sampling link and the pulse-width modulation link on the impedance characteristics.The result shows that it is easier to misjudge the system instability in the high frequency range if its effect is not considered.Finally,the built model obtains its harmonic domain impedance comparison with the impedance sweep frequency measurement method to determine the correctness of the built harmonic domain impedance model.This model lays the foundation for analyzing the mechanism of resonance instability of the electrified high-speed railway vehicle-network coupling system and designing instability suppression strategies.Then,based on the built harmonic domain impedance model,the resonance instability mechanism of the electrified high-speed railway vehicle-network coupling system is analyzed.This chapter first briefly analyzes the impedance analysis principle of the resonance stability of the vehicle-network coupling system,and then simply converts the harmonic domain impedance model built in this article into an equivalent single-input single-output impedance model based on mathematical matrix transformation.It not only retains the accuracy of the impedance model built,but also makes the analysis and measurement process simple and effective.The measurement result verifies the accuracy of the model and compares and analyzes the difference and connection of the impedance model characteristics of different documents.Finally,use the derived equivalent single-input single-output impedance model to analyze and summarize the effects of various parameters in the system on the stability of the system.The consistency between the simulation results and the theoretical analysis verifies the analysis of the resonance instability mechanism.Accuracy,and use this as a basis to put forward proposals for actual project construction and operation,and provide ideas for resonance instability suppression strategies.Finally,the study of instability suppression is carried out from the following two perspectives: The first method is to propose an instability suppression method that considers the optimization of control parameters.The result of this design is that when the control cannot be changed at the design stage,it only relies on parameter adjustment to support the stable operation of the system with a large range of impedance on the power supply network side as much as possible.At the beginning of the method,the parameters of the current compensator and the DC side voltage outer loop compensator are designed under the influence of delay.Secondly,the integrated power supply network strength,the parameters of the phase-locked loop compensator and the system stability margin are designed to ensure the control parameters of stable operation within a certain grid-side strength range.The results show that there are certain limitations in the optimization of control parameters.The simulation results verify the effectiveness and limitations of the proposed instability suppression method considering the optimization of control parameters.The second method uses the frequency domain passivity theory to propose an impedance-based passive enhancement method of instability suppression.It can solve the problem that the current inner loop and the phase-locked loop outer loop are coupled with each other due to the system delay,which affects the system interaction stability.The proposed passive enhanced instability suppression control can decouple the current inner loop and lock only through simple open-loop feedforward compensation without knowing the network side information and without introducing a complex and cumbersome new control framework.The phase loop outer loop reshapes the passive characteristics of the vehicle side impedance,thereby ensuring the stability of the vehicle-network coupling system.The simulation results verify the effectiveness of the proposed impedance-based passive enhancement method of instability suppression.Finally,by building a corresponding low-power physical platform,the effectiveness of the proposed resonance instability suppression method is further verified.