Research On Harmonic Suppression And Reactive Power Compensation Of Metro Traction Power Supply System

With the completion of the first urban subway in the world in the 19th century-the British metropolitan subway,the subway has become an indispensable mode of urban transportation.The development of subway in China is relatively mature.Compared with other urban transportation modes,subway has the characteristics of fast operation speed,large transportation flow and almost no environmental pollution.With the continuous increase of subway operating mileage in China,the harmonic pollution and reactive power problems in subway traction power supply system have a great impact on the power quality of public power grid.Based on the harmonic pollution and reactive power problems generated by metro traction power supply system,this paper proposes to use active power filter（APF）and static var generator（SVG）to control the harmonic pollution and reactive power problems of metro traction power supply system respectively.Based on the analysis of the working principles of APF and SVG,the corresponding mathematical models are constructed,The parameters of its components are calculated,the reference command current detection method is studied,the respective control strategies of APF and SVG are studied,and the simulation model is built by Matlab/Simulink software for verification.In the research of reference command current detection method,firstly,the instantaneous reactive power theory widely used in three-phase system is introduced,and the i_p-i_qdetection method developed on the basis of instantaneous reactive power theory is further studied,It is found that there is a frequency doubling component in the output current signal of the low pass filter（LPF）used in the i_p-i_qdetection method based on the instantaneous reactive power theory.To solve this problem,this paper uses the notch filter to filter the frequency doubling component and improve the accuracy of the detection process.Aiming at the problem of high delay caused by coordinate transformation in i_p-i_qdetection method based on instantaneous reactive power theory,a virtual i_p-i_qdetection method without coordinate transformation is proposedβImproved i_p-i_qdetection method of phase.Finally,Matlab/Simulink software simulation shows that the improved i_p-i_qdetection method has the advantages of good real-time performance and high accuracy.In the research of APF and SVG control strategies,in the research of APF control strategies,the working principles of traditional proportional integral（PI）controller and quasi proportional resonance（QPR）controller are analyzed,and PI+QPR comprehensive control strategy is proposed to track and control the compensation current output by APF,QPR controller is used to accurately track the third harmonic of harmonic current,while PI controller is still used to track and control the other harmonic currents.In the research of SVG control strategy,two common control methods,indirect control of compensation current and direct control of compensation current,are introduced.Aiming at the problem that indirect control needs to track and control SVG compensation current through intermediate variables,the direct control method of tracking and controlling SVG compensation current without intermediate variables is selected,This control method not only has high response speed,but also reduces the detection error of the system.In the research of APF and SVG cooperative control strategy,in order to make rational use of the compensation capacity of APF and SVG,a cooperative control mode is proposed to optimize the configuration of reference command current and improve the accuracy of compensation.Finally,the corresponding simulation models are established according to their control strategies.Finally,the Matlab/Simulink platform was used to establish simulation models respectively.The feasibility of the respective control strategies of APF and SVG was verified by the simulation under three conditions,namely,no governance measures were taken,APF was invested separately and APF and SVG were invested simultaneously.The simulation results show that the compensation capacity of APF and SVG is fully utilized,the harmonic content of the system is obviously reduced,and the reactive power compensation effect is remarkable.