| With the continuous improvement of the urban development process,the subway,as the main system for the development of urban rail transit in China,has ushered in an unprecedented development,and the safe and stable operation of the metro traction drive system(MTDS)has received extensive attention.Limited by the space and weight of the onboard converter device,the dc-link input filter usually selects a larger inductance and a smaller capacitor to achieve a better filtering effect.However,this kind of filter has the problem of weak damping.Simultaneously,the inverter-motor drive system exhibits negative impedance characteristics under constant power control,which will cause the vehicle-grid system impedance mismatch and further reduce system damping.Therefore,the subway traction drive system will have LC resonance on the DC side under certain operating conditions,which will affect the safe and stable operation of the train.Therefore,it is of great significance to establish a model that can accurately analyze the subway traction drive system’s harmonic characteristics and design a suppression strategy.This article first briefly introduces the basic mathematical model of the MTDS and constructs the characteristic equation model and the impedance model based on the Linear Time-Invariant(LTI)system theory.The accuracy of the LTI model is verified by impedance measurement.Combining time-domain simulation and the LTI impedance model,dc-link input filter parameters and motor operating conditions on system stability are analyzed.Considering that the inverter-motor drive system presents a periodic trajectory in the steady-state,the Harmonic State-Space(HSS)model of the MTDS is constructed based on the Linear Time-Periodic(LTP)system theory to accurately describe the non-linear parts such as inverter switching characteristics and coordinate transformation.The method of reconstructing the harmonic domain HSS model in the time domain with Simulink based on the Multi-dq modeling theory is studied.The accuracy of the proposed LTP model of the MTDS is verified by impedance measurement and time-domain reconstruction.Based on the characteristic equation model,the LTI impedance model,and the HSS model,the stability boundary of the system operating conditions and the critical value of the input filter parameters are adjusted.Based on active damping control,focusing on compensating the damping of the DC side input filter and inverter-motor drive system,the active damping suppression strategy based on virtual positive impedance and virtual resistance are studied,respectively.For these two suppression strategies,the closed-loop system’s HSS model is constructed separately,and the active damping controller parameters are tuned through the HSS model.Simulation-based on Simulink verifies the effectiveness of the proposed suppression strategy in the full speed range.Finally,a low-power inverter-motor drive system experimental platform using TMS320F28335 DSP controller is built.Based on this platform,the LC resonance phenomenon on the DC side was reproduced,and the active damping suppression strategy program based on vector control was completed.A low-power experimental platform verifies the effectiveness of the proposed active damping suppression strategy. |
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