Research On Continuous Co-phase Power Supply System Based On Three-phase To Single-phase Converter

As a momentous mode of travel and freight transportation,railroad is be closely bound up with the development strategy of the country and the daily life of the nation.With the implementation of the "eight vertical and eight horizontal" railroad network planning,China’s railroad transportation is developing towards electrification,high-speed and heavy-duty.Traction power supply system is the power core of electrified railroad,and at present,the traditional traction power supply system not only has many power quality problems,but also the electric phase separation set in the system seriously restricts the development of high-speed and heavy-haul railroad.In recent years,the research in the Domain of power electronics and multi-level technology is changing day by day,and the emergence of through-phase homogeneous power supply technology based on three-phase to single-phase converter has brought an opportunity to solve the power quality problems in the traction power supply system.In high-capacity and high-power applications,the modular multilevel converter(MMC)has advantages over the common three-level converter,which not only can reduce the cost but also improve the quality of output voltage,so MMC is applied to the through-phase traction power supply system.In this paper,the through-phase homogeneous traction power supply system based on MMC three-phase to single-phase converter is investigated.The main work is as follows.Firstly,the current status of the development of multilevel converter and through-phase power supply system is introduced.The three modes of operation of the MMC submodule in the system are also analyzed.In order to study the four-quadrant operating characteristics of the MMC,this paper investigates the single-phase MMC from both a mathematical model and an equivalent circuit diagram.The mechanism of inter-phase circulating current generation and its effects on the three-phase side and single-phase side of the converter are analyzed,and the corresponding suppression measures are taken.Next,the topology of the MMC three-phase-single-phase converter is studied and its operating principle is analyzed.The control strategies of the three-phase rectifier side and the single-phase inverter side of the MMC three-phase to single-phase converter are introduced.A double closed-loop control strategy based on active and reactive current decoupling is used to control the rectifier side,and a voltage RMS-based control strategy is used to control the inverter side.Then,the impedance analysis of the through-phase same-phase traction power supply system is carried out,and the mechanism of circulating current generation among traction substations is analyzed,and the simulation model of three power sources on the grid is built in Multisim simulation software for simulation verification;for traction substations distributed in different geographical locations,consistent output voltage cannot be achieved without adding additional communication lines,therefore,this paper proposes a Beidou-based Therefore,this paper proposes a multi-converter grid-connection control strategy based on Bei Dou satellite navigation system(BDS)with self-synchronization of second pulses.The simulation is carried out to verify the feasibility of the strategy.Finally,the MMC three-phase to single-phase converter is modeled and simulated using the Matlabl/simulink simulation platform.The dynamic and steady-state results of the rectifier-side and inverter-side output voltages of the system under various operating conditions are analyzed,and the correctness of the system control strategy is demonstrated.