Electrical Stability Analysis Of Vehicle-Grid Coupling System Based On Impedance Modeling In Harmonic Domain

The train-to-network coupling system formed by the coupling of the high-speed railway EMU and the traction network has typical nonlinear time-varying characteristics,and the complex harmonic coupling relationship within the system may lead to serious electrical stability problems.Aiming at the stability problem of the existing vehicle-network coupling system,it mainly focuses on the harmonic distortion near the fundamental frequency of the low-frequency band and the harmonic distortion phenomenon related to the switching frequency of the high-frequency band.To study the electrical stability of the vehicle-network coupled system,this paper attempts to model based on Harmonic State-Space,to study the harmonic coupling process existing in the vehicle-grid coupling system as a nonlinear timeperiodic system and establish a full-frequency domain small-signal impedance model in the harmonic domain of the vehicle-to-grid coupled system.To analyze the harmonic distortion of the fundamental frequency and low-frequency disturbances in the vehicle-to-grid coupling system in the low frequency band,using the HSS modeling method to derive the Multi-Input Multi-Output harmonic domain low-frequency impedance model of the equivalent single rectifier on the vehicle side,study the phenomenon of single fundamental frequency transfer and frequency coupling in the system caused by Park transformation in the vehicle side controller.Through the harmonic transfer relationship between the traction network and the onboard rectifier,the established MIMO impedance model is converted into an equivalent Single-Input Single-Output harmonic domain impedance model that retains all harmonic coupling information,which further simplifies the impedance verification and impedance-based stability analysis process.Aiming at the high-order harmonic distortion phenomenon in the high frequency band of the vehicle rectifier,the coupling mechanism of the middle switching frequency and the fundamental frequency generated by the PWM modulation process is studied in detail;Furthermore,the HSS modeling method is used to establish the small-signal model in the harmonic domain,and the coupling transfer process between the fundamental frequency,switching frequency,and disturbance frequency in the PWM modulation process is analyzed.The harmonic signal flow diagram is used to fully display the frequency harmonic coupling and frequency transfer harmonic transfer process inside the rectifier,and the obtained harmonic domain low frequency impedance model is extended to the full frequency domain stage.The obtained equivalent SISO harmonic domain impedance model is verified by MATLAB/Simulink platform.Unified analysis of the low-frequency oscillation and high-frequency resonance of the vehicle-to-grid coupling system is carried out.The obtained harmonic domain impedance model is used to qualitatively analyze the influence of each system parameter and control parameter on the system stability in the system,and further quantitatively determine the stability margin of each parameter.Then,the distributed capacitance and the obtained impedance model of the traction network are introduced to analyze the high-frequency harmonic resonance of the vehicle-to-grid system,and the generation mechanism of the highfrequency harmonic resonance of the vehicle-to-grid coupling system is analyzed;Through the MATLAB/Simulink platform and the Hardware-In-the-Loop simulation platform,the stability analysis results are verified in this paper.