| Low carbon environmental protection,energy saving and emission reduction are the future development trend of urban rail transit(later referred to as urban rail)traction power supply system,among which the rational use of regenerative braking energy and the new energy-fed traction power supply system have become hot spots for research.In this thesis,we optimize the energy-saving control strategies in the traction power supply system of urban railways to reduce the energy consumption and operation cost of the system.Firstly,we investigated the development status and existing problems of urban railways,and the significance of the topic based on the dynamic simulation platform to optimize the energy saving control of urban railways,and investigated the current status of the simulation platform and existing control research.An overview of the kinematic simulation platform is given,the topology of the main and control circuits of the kinematic simulation platform is briefly described,and the functions of the main components of the platform are also described.Next,the mathematical modeling of the main components in the kinematic simulation platform is carried out,and the kinematic simulation platform is divided into AC system and DC system,which are discussed separately,focusing on the derivation of the mathematical model of the energy feedback device(energy-feeding unit)composed of PWM(Pulse Width Modulation)rectifier,and finally the equivalent model of the DC system is obtained.Then,based on the obtained equivalent model,the optimal control of the system is discussed separately under traction and braking conditions.The objectives of the optimal control are given to address the shortcomings of the current scheme of the system.The main objective of the optimal control under traction conditions is to solve the problems of severe voltage fluctuations on the DC side of the system and the lack of capacity of the old traction power supply system,while the objective of the optimal control under braking conditions is to improve the utilization of regenerative braking energy of the train,reduce the switching losses of the energy feeder unit,the losses of the transmission line and the energy returned to the higher power grid.The mainstream control strategy applied at present is analyzed theoretically,and the scheme of cooperative power supply and distributed cooperative absorption is proposed for further in-depth study by combining the optimal control objectives and existing sag control theory.Finally,a simulation model is built in MATLAB/Simulink environment based on the system composition of the kinetic simulation platform to verify the accuracy of the built mathematical model,and the output characteristics of the energy-fed unit and rectifier unit are simulated and verified respectively.Based on the kinematic simulation platform,the full physical simulation experiments are conducted to compare the results of theoretical calculation,software simulation and full physical simulation and analyze the reasons for the gap.Through full-cycle and full-factor train operation simulation experiments,the effectiveness of the proposed optimal control strategy is verified.There are 73 figures,15 tables,and 60 references. |
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