Analysis Of Double Star Multilevel Single-three-phase Combined Inphase Power Supply System

With the development of the electrified railway in the direction of high speed and heavy load,the problem of power quality with negative sequence in traction power supply system is becoming more and more prominent,and the development of the same phase power supply technology solves the above problems.The same phase power supply technology of single three-phase combination makes it possible to reduce the capacity of the same phase compensator effectively under the precondition of satisfying the standard of power quality,especially its irreplaceable advantages in the reconstruction of existing lines.The modular multilevel(MMC)technology has a strong application prospect in high voltage and large capacity converters,and the MMC converter can be hung directly on the traction bus,eliminating the traction matching transformer and reducing the investment cost.Double star multilevel converter(DSMC)is a new topology based on the existing MMC structure,which is applied to the same phase power supply system of single three-phase combination mode,without reducing the compensation capability,to a greater extent reduce the number of converter components,reduce the volume of the same phase compensation device,reduce the cost of railway construction investment.Therefore,this paper is based on the dual-star multilevel structure converter single phase combined with phase power supply system.In this paper,the structure and characteristics of single-phase combined and single phase combined phase power supply system are compared by comparing the structure of combined phase power supply system with the utilization ratio of transformer winding capacity.The equilibrium condition of single three phase combined phase power supply system is studied,and the optimal compensation algorithm of single three phase combined phase power supply system is given based on the international standard of power quality.This paper analyzes the difference between the capacitance voltage,the control strategy,the working principle and the number of sub modules of the MMC converter based on the MMC topology,analyses the DSMC converter topology,studies its equivalent model,the balance transformation principle and the power characteristic.Combining the current control strategy with the improved carrier phase-shift modulation strategy,a layered control strategy is designed for the upper compensationcurrent control of DSMC and the lower power module input resection control.Using Matlab/simulink simulation platform to build the topological model presented in this paper,simulate the change of the same phase power supply system based on the single three-phase combination of DSMC and before and after putting into the same-phase power supply device,the simulation verifies the correctness and the effectiveness of the control strategy,and provides theoretical support for practical application.