Research On The Secondary Pulsation For Hybrid EMU

At present,most of the power supply mode of the EMUs is single-phase AC power supply.The EMUs convert AC to DC through single-phase four quadrant converter.The instantaneous power output from the power grid to rectifier will include steady-state DC power and secondary pulse power.Secondary pulse power will cause secondary pulsation in the intermediate DC link,which will affect the control performance of the later converters.In order to reduce the secondary pulsation,the LC resonant branch is usually connected in parallel to the DC side of the high-speed train to provide a loop for the secondary pulsation power.The secondary pulsation can also be reduced by increasing the capacity of the DC side supporting capacitor.However,the above method will reduce the overall power density of the locomotive and increase the volume and weight,which is not conducive to lightweight design.Moreover,the parameters of the LC resonant branch will change,and its resonance point will shift.Therefore,the cancellation of LC resonant branch will be the development trend,but also the current research focus.Based on the hybrid EMU project,this paper studies the secondary pulsation problem of the hybrid EMU.The goal is to realize the stable operation of the hybrid EMU without LC resonant circuit and improve the power density of the hybrid EMU.Aiming at the problem of secondary pulsation,a time-division multiplexing hybrid EMU bi-directional DC/DC converter is proposed to suppress the secondary pulsation of DC bus,and a method to obtain the secondary pulsation power based on the detection of DC bus voltage is proposed.The voltage and current double closed-loop control is designed to realize the effective tracking of the instruction voltage.Realize the secondary pulsation suppression of the middle DC side of hybrid EMU.At the same time,considering the adverse effect of the secondary pulsation of the DC bus voltage on the converter when the bidirectional DC/DC converter is not inhibited by the secondary pulsation,the problem of the harmonics on the grid side of the four-quadrant converter is analyzed,and an improved four-quadrant converter control scheme is proposed according to the source of the harmonics on the grid side.The influence of the secondary pulsation on the three-phase output voltage of the auxiliary inverter is analyzed and the optimal control method of the DC bus voltage feedforward is proposed.The simulation model of matlab/simulink is built to simulate and verify the relevant converters of hybrid EMU.At the same time,the experimental verification is carried out based on the traction converter experimental platform and auxiliary converter experimental platform of EMU.The simulation and experimental results show the feasibility of the proposed scheme.96 figures,3 tables,60 references.