Research On Modeling And Protection Of Metro DC Traction Power Supply System

Urban rail transits have been vigorously built in order to tackle the issue of traffic congestion.To ensure that these transits operate in a stable fashion,an effective metro power supply is critical.The failure of the traction power supply system can cause substantial economic losses to operator and municipality.At the same time,such failures can potentially endanger passengers’ personal and property safety and disrupt the normal operation of society.Therefore,probing metro traction power supply system faults in depth and improving the protection methods counteracting such failures can provide important theoretical and practical insights so that the orderly and stable operation of urban rail transits can be achieved.Addressing these problems and taking the Xi’an Metro as an example,this thesis studies the structures and operation principles of its supply system and,using a simulation model,and looks into possible faults and fault protection.Specific research contents of this thesis are as follows:1)A simulation model of Xi’an Metro Line 4 was generated in order to provide a theoretical basis for metro operation,fault modelling and protection research of power supply systems.In particular,the high voltage system and medium voltage ring network system and the operation principle of the traction power supply system,as well as its main circuit topological structure have been described in detail.In addition,the train AC drive mechanism of the metro power supply system has been built.At the same time,the action of protection control switches when the equipment of each voltage level fails has been analysed.2)The main sub-stations,rectifier modules,traction network and train transmission system of metro traction power supply systems are modelled.The mathematical model of the metro traction power supply system is then verified by using MATLAB/Simulink simulation software.The simulation results show that the expected model is consistent with the actual output,and also the waveform of the catenary output conforms to the actual situation.At the same time,the train model with loads on the traction power supply system is also consistent with the actual working conditions.The results underline the validity and feasibility of the simulation model,and provide an experimental basis for research on traction power supply system short-circuit faults and protection against such faults.3)Short circuit fault analysis and simulation of short circuit currents in traction power supply system were undertaken under unilateral and bilateral power supply scenarios.The simulation results show that the rate of short-circuit current rises decays according to an exponential function.With respect to actual short-circuit current faults,studying the basic principles of feeder protection mechanism,overcurrent protection,and ROR current rate of change protection is necessary.In view of the inflexibility of threshold settings for the protection method based on current integral values and the ratio of current mean value to peak value,a fuzzy reasoning-based protection algorithm is proposed.Such an algorithm can protect the safety of power supply system and avoid malfunctioning supply protection which could be caused by an excessive train starting current.Finally,the correctness of the model and the effectiveness of the protection under metal faults are verified by a case study from an actual fault of the Xi’an Metro.