The Research On Three-phase Load Unbalance Compensation Technology Of High-speed Railway Traction Power Supply System

In recent years,the construction and development of high-speed railway is more and more rapid,which has become the most important way of transportation and travel.The traditional electrified railway has the problem of three-phase load imbalance due to the structure of traction power supply system.Compared with the traditional electrified railway,the load power of highspeed railway is larger,the departure frequency is higher,and the imbalance caused by it is more serious.Negative sequence current will seriously affect the safe and stable operation of power system in terms of power generation,transmission,distribution,etc.;In addition,the EMUs running on high-speed railway will adopt regenerative braking mode when braking,while the regenerative braking energy is not effectively used in the traction network at present,and most of the regenerative braking energy is fed back to the grid,which deteriorates the imbalance of high-speed railway.However,the large capacity and high cost of the compensation device restrict its wide application to a great extent.Therefore,it is necessary to study the unbalanced compensation technology of high-speed railway traction power supply system.The main contents of this paper are as follows:(1)The cause and harm of three-phase load imbalance,the problem of regenerative braking power feedback and the situation of traction transformer connected to power grid by alternating phase are analyzed in detail.On this basis,this paper summarizes the research status of threephase load imbalance compensation technology of traction power supply system,classifies the existing compensation technology,summarizes their advantages and disadvantages,discusses the different methods of traction power supply system for the utilization of regenerative braking energy,and points out the advantages and disadvantages of various methods,and finally expounds the significance of this study.(2)In view of the power feedback of high-speed railway,an electromagnetic hybrid unbalance compensation system is proposed.The influence of power feedback on negative sequence current under different working conditions is studied;the topological structure of hybrid compensation system is proposed,and the working principle of hybrid system cooperative compensation is discussed according to the response speed and characteristics of different compensation devices;according to the working principle of cooperative compensation,the respective compensation reference current of two sets of devices is deduced,and the control system and minimum of hybrid compensation are designed Finally,the effectiveness of the proposed method is verified by simulations and experiments.(3)In view of the fact that it is difficult to further reduce the installed capacity of the unbalanced compensation device by the single station unbalanced compensation method,a multi station coordinated unbalanced compensation system for high-speed railway is proposed.The conventional Steinmetz and RPC imbalance compensation principle is proposed based on the treatment of single station negative sequence current,which is not suitable for multi station coordinated compensation.Therefore,a direct injection method which is more suitable for multi station cooperative compensation is proposed.This paper studies the working principle of multi station cooperative compensation,deduces and calculates the total negative sequence current of multiple stations and the negative sequence current that each station compensation device needs to compensate,and proves theoretically that the multi station cooperative compensation method can reduce the installation capacity of a single station compensation device by 1/3.In order to reduce the communication requirements of the whole system and improve its reliability,a control strategy based on multi-agent is proposed and a multi station cooperative control system is designed.Finally,the effectiveness and advantages of multi station cooperative compensation are verified by simulations and experiments.(4)In order to improve the utilization of regenerative braking energy and traction transformer by adding energy storage in high-speed railway,an unbalanced compensation system of high-speed railway considering energy storage is proposed.The topological structure of energy storage unit is analyzed based on the unbalanced compensation device.In order to make the two functions of energy storage and imbalance compensation not affect each other,the possibility of decoupling control of the two functions is analyzed,and the corresponding decoupling control method is studied.Through the analysis of the capacity and power of the device,it is found that the decoupling control not only enables the two functions to be flexibly controlled according to the actual demand,but also reduces the installed capacity of the compensation device by 15.47% when the power of the energy storage unit is fixed.Finally,the simulation and experiment results show that the system can flexibly compensate the imbalance and energy storage without affecting each other.According to the characteristics of high-speed railway,the three-phase load imbalance compensation technology of high-speed railway is studied in this paper,which further enriches the theory and technical system of power quality compensation of traction power supply system,and adds a guarantee for the rapid development of high-speed railway.