Research On Active Compensation Method For Power Quality Of Electric Traction System Based On MMC-RPC

Railway,as a green transportation mode,its level of development has become one of the standards to measure whether a country is advanced.Today,the development level of China’s railway has approached the ranks of first-class countries,and its mileage and scale have far surpassed other countries,and it has become one of the Chinese brands going global.However,with the development of electrified railways in my country,there are increasingly serious power quality problems.After the negative sequence,harmonics,and reactive power are injected into the power system,it will seriously affect the normal operation of locomotives,and even cause immeasurable damage to the power system.loss.Railway power condition(RPC),which balances the system by adjusting the harmonics,active and reactive power of the power supply arms on both sides,has become a power quality compensation device with higher efficiency and better performance.The thesis uses a multi-modular railway power condition(MMC-RPC)to adjust the power quality of the electric traction power supply system.The use of this topology makes up for the shortcomings of traditional railway power regulators that have insufficient compensation capacity and low switching frequency.The modular converter replaces the voltage source converter on both sides of the DC capacitor,and is directly connected to the power supply arms on both sides,eliminating the need for step-down transformers,improving economic benefits,and the use of modularization makes the switching frequency more High,the compensation effect far exceeds that of traditional power regulators.The main circuit structure of the thesis is to change the 110kV three-phase high voltage into 27.5kV double unidirectional through the V/v traction transformer.Starting from the structure,the thesis analyzes the principle of the V/v traction transformer,and expounds the harmonic characteristics and negative sequence characteristics of the electric traction system based on the Vv traction transformer.Next is the principle analysis of the MMC module.For the 3-leg MMC-RPC,the thesis analyzes its voltage,current and power and establishes the abc coordinate system,αβ coordinate system and the single-phase MMC based on its topology.Mathematical model in dq axis coordinate system.For the 3-arm MMC-RPC,a two-layer control strategy based on sliding mode inverse is proposed.The control strategy adopts the idea of two-layer control,and decomposes it into upper and lower double layers from the perspective of compensation current.The upper layer adopts the nearest electric current.The principle of flat approximation is used for control,and the lower layer adopts sliding mode inverse control strategy to achieve control.The control method is simple,clear,robust and highly flexible.At the end of the thesis,the proposed control system is designed,including the main circuit parameter design,hardware circuit design and software design of the MMC-RPC system,and the simulation model is established through MATLAB/Simulink,from the three aspects of compensation effect,DC side and circulating current.The system is analyzed,and the simulation results illustrate the feasibility and accuracy of the control system proposed in the thesis.