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

At present,there are some power quality problems,for instance,reactive power,harmonics and negative sequence in the electrified railway power supply system.The existence of the neutral section devices in the traction network greatly limits the development of the capability of speed and load of the locomotive.The continuous co-phase traction power supply system based on three-phase to single-phase converter realizes the three-phase to single-phase conversion through controllable power electronic devices,which can totally cancel the neutral section devices and solve the power quality problems better,and the traction network can be linked up completely.In this paper,the continuous co-phase power supply system of three-phase to single-phase converter based on MMC structure is studied,and the feasibility of the system is verified through the aspects of theoretical evaluation and simulation.In order to study the feasibility of the continuous co-phase traction power supply system of three-phase to single-phase converter based on MMC structure,first of all,the paper analyzes the topology structure and working principle of MMC sub-module.The mathematical model of the single-bridge arm of MMC sub-module is established,and its capacitance voltage equalization control strategy,circulating current suppressing strategy based on PI,and modulation strategy of MMC are studied.Secondly,on that basis,the topology structure and working principle of the three-phase seven-level PWM converter and single-phase seven-level PWM converter based on MMC structure are analyzed independently.The three-phase active reactive power decoupling control strategy based on dq coordinates for the three-phase PWM converter and the single-phase dq decoupling control strategy for the single-phase PWM converter are researched.Finally,through the above research,the parameters of the continuous co-phase power supply system of three-phase to single-phase converter based on MMC structure are calculated,and the parameters of sub-module capacitance and bridge arm inductance are designed.The topology of the grid is studied and the impedance model of the traction network is evaluated and establishedOn Matlab/Simulink simulation platform,the simulation models of a three-phase PWM rectifier,a single-phase PWM inverter and a continuous co-phase traction power supply system of three-phase to single-phase converter based on MMC structure connected to three substations are set up.The simulation results prove the theoretical analysis and the validity and correctness of the main circuit structure,modulation strategy and control strategy of the system,and traction substations can realize grid-connected completely,while,the system has good steady-state and dynamic performance.It indicates that the system can cancel the neutral section devices and achieve the consecutive power supply.