Research On Hybrid Power Quality Control System For Electrified Railway

As an important indicator to measure a country’s infrastructure,electrified railway plays an important role in promoting national economy.However,as a highpower single-phase rectification load,the electric locomotive produces negative sequence current,reactive power,harmonic current,etc.,which seriously affects the power quality of the traction power supply system.The rapid development of high-speed railways mitigates harmonic pollution,while brings a more serious negative sequence current issues.The existing power quality adjustment methods demand excessive compensation capacity but can’t solve the power quality problem entirely.In view of that,an asymmetrical connection balance transformer based hybrid power quality control system for electrified railway(ACBT-HPQCS)has been proposed in this paper,and its topology structure,parameter design and control method has also been analyzed.Firstly,based on the measured data of a traction substation,the relationship between the three-phase unbalance rate,reactive power and voltage fluctuations in the traction power supply system is analyzed,which provides a realistic basis and entry point for subsequent research.In order to optimize the existing adjustment technology,the advantages and disadvantages of the existing control measures such as optimizing the traction power supply mode,installing the passive compensation device,installing the active compensation device and installing the power flow controller are analyzed.Then,based on the shortcomings of the existing adjustment methods,combined with the good negative sequence current suppression effect of the balance transformer,a power quality hybrid regulation system using asymmetric connection balance transformer is proposed.The system fully utilizes the negative sequence current suppression capability of the balance transformer,and combines the advantages of the inductively filtered rectifier transformer(IFRT)to skillfully integrate the passive branch with the back-to-back converter system,effectively reducing the capacity of the active device..In order to adapt to the strong time-varying and nonlinear characteristics of the traction power supply system,the advantages and disadvantages of several nonlinear control methods are analyzed.Based on the passivity of the converter system,the damping injection control method based on the Euler-Lagrangian model is finally adopted to control the converter system.This control method flexibly adjusts the tracking speed by changing the injection damping,and has strong anti-interference ability.Finally,based on the above research,the simulation model of the proposed power quality hybrid control system is established by MATLAB/Simulink.The simulation analysis is operated under the two-side load and one-side load conditions respectively.The simulation results verify the outstanding ability of the hybrid regulation system to reduce active device capacity and improve power quality.It also reflects the effectiveness of the proposed control method.In order to analyze the engineering availability of the system,a small-capacity experimental system is established,and the device parameters,wiring principle,platform debugging and control system implementation has been illustrated.The experimental results also show that the adjustment system can effectively reduce the capacity requirements of active devices,significantly reduce investment costs,an d has certain engineering application value.