Comprehensive Optimization Strategy Of Coupled Stability Of Train-Network In Electric Railways

In recent years,the safe and stable operation of electric railways has attracted more and more attention,especially the train-network coupled stability problem focusing on train-network high-frequency resonance(HFR)and low-frequency oscillation(LFO),which has become the core of research.This paper analyzes coupled stability of train-network in electric railways from four aspects: the impedance modeling of train-network,stability and mechanism analysis,the network-side converter control strategy suppression methods and the modulation strategy suppression methods are studied and discussed.The main research results are as follows:Firstly,based on all frequency rotating-coordinate system(AF-RCS),train-network impedance small-signal model is proposed.The model considers the d and q-axis coupling effect of impedance,and reflects the influence of variables of train and traction network on the system,optimizes the inaccuracy in existing models;it considers the simplified impedance model of inverter and traction motors,improves the incomplete problem in existing model;it unifies the impedance forms in high frequency and low frequency,and solves the problem that the unstable mechanism is not comprehensive due to the inconsistency of the high and low frequency impedance model forms.Secondly,based on the AF-RCS train-network impedance small-signal model,the stability and mechanism of train-network coupling are analyzed.For a new type of EMU,the influence of traction network parameters on the stability of the system is studied,and the theoretical reference can be provided for other EMUs.By analyzing the stability from train position,the traction network equivalent parameters,the network-side converter voltage loop and current loop control parameters,and the number of trains,the HFR and LFO mechanism is proposed and summerized.It is clear that the insufficient system damping is an important factor causing the instability of the system in whole frequency.The relationship provides a theoretical basis for the study of suppression measures against both HFR and LFO.Thirdly,based on the AF-RCS train-network impedance small-signal model and the instability mechanism,measures to suppress both HFR and LFO are proposed from the perspective of the network-side converter control strategy.The active oscillation compensation(AOC)suppression measure is proposed to improve the system damping,solves the problem of unstable train-network coupling caused by insufficient system damping.The voltage constant transient(VCT)control is further proposed.The VCT has short adjusting time which can protect the system in time.For the type and degree of train-network coupled instability,VCT-AOC comprehensive suppression strategy is finally proposed,which both enhances the damping ratio and realizes fast protection.Finally,based on the instability mechanism,two measures to suppress HFR are proposed from the perspective of network-side converter modulation strategy.Based on the improvement of common modulation strategies,periodic control carrier phase-shift pulse width modulation(PCCPS-PWM)is proposed,which solves the problem of HFR caused by inaccurate phase shift angles between network-side converters.The strategy is simple and easy,but can not suppress HFR of all cases.For the problem of wide harmonic band in the traction network,the windowed resonant harmonic elimination total harmonic distortion minimization modulation(WT-PWM)is further proposed.The non-fixed frequency resonance suppression is realized by the cooperation of a based window and a moving window.On this basis,the THDM algorithm is proposed to reduce the total harmonic distortion(THD)of the network voltage.The possibility of HFR is reduced as much as possible.For all of the theories,models and approaches above,there are corresponding simulated and experimental results,explaining their applicability and validity.104 figures,13 tables,185 references...