Modeling And Simulation Of AC/DC Power Supply System For Urban Rail Transit Based On MATLAB/Simulink

With the continuous development of national economy and the acceleration of urbanization,the construction of modern rail transit has become the best choice to relieve traffic congestion in many big cities.In few years,the urban rail transit construction will usher in its golden era.Therefore,improving the technology of the urban rail transit and carrying out the theoretical research of the power supply system have become the focus of the current discussion.Using MATLAB/Simulink to simulate the AC/DC power supply system is considered as a steady-state and dynamic response of power system under different conditions and provides the basis for the system design and operation,which is of great theoretical guiding and practical significance.In this thesis,the modules of AC/DC power supply system are introduced in detail first.The simulation is then performed for verifying the important parts of the modules.The AC network model in the system consists of the external power supply,the main substation,the step-down substation and the medium voltage power supply network.For modeling the main transformer and distribution transformer,the formula for calculating the model parameters is proposed based on the relationship between mathematical model and simulation model of two windings transformer,and the correctness of the transformation formula is verified by the experimental simulation model.And for modeling the static var generator,according to the basic principles,a synchronous rotating double closed loop SVG model based on SVPWM modulation using the direct current control strategy is built,its composition ability is then simulated in this thesis.The DC network model consists of the DC traction substation,the traction network and the train.This thesis focuses on the modeling of rectifier unit.By analyzing the working principles of 6,12,24 pulse rectifier unit,the simulation models are constructed respectively.Then parameter setting method of splitting winding transformer,the position of the phase-shifting transformer and the influence of overvoltage protection device on the output are discussed in detail.According to such system analysis and the simulation results,the model of the power supply system of Shenzhen Metro Line 11 is simulated based on its structure and the whole system is verified by comparing with the test data.During normal operation,the simulation of model's voltage and current distribution has a good agreement with the measurement result in Shenzhen Metro.In addition,a comparison among the simulation characteristic curve of the 12 and 24 pulse rectifier unit,the measured characteristic curve from Shenzhen Metro Line 11 Che Kung Temple traction substation and the characteristic curve drawing by theoretical formula is made.Different from the theoretical characteristic curve,the simulation and measured curves of the two kinds of rectifier units show a more similar result which generates a bend at the transition current.Thus,the accuracy of the rectifier unit model is verified in this thesis.At the end of the thesis,the change of short circuit current is analyzed in steady state and transient state.Considering the influence of the transient current,the working state of the rectifier unit is analyzed and the calculation method of the steady current is improved.The thesis also simulates the transient process of the short circuit current in AC/DC network when the short-circuit point is in different positions,which improves the theory of short circuit fault calculation.