Fault Diagnosis And System Reconfiguration Strategy Of Advanced Co-Phase Traction Power Supply System Based On Cascaded Converter

In advanced co-phase traction power supply system,the three-phase to single-phase converter-based substation is adopted in this system.Compared with traditional two-phase feeding scheme,single-phase feeding connection scheme is applied to improve the abilities of power supply and solve the power quality problems.In this thesis,fault diagnosis and fault handling strategies of the three-phase to single-phase converter-based substation are studied.The simulation and experimental results verify the viability and effectiveness of the proposed strategies.First,the operational principle,circuit topology and control strategies of the three-phase to single-phase converter are analysed.The mathematical model of three-phase voltage source PWM rectifier between d and q axes,the operating principle of diode-clamp cascaded multilevel inverter and closed loop control strategy are studied.Carrier disposition modulation technology and carrier phase-shifted modulation are introduced.The harmonic characteristics of these modulation strategies are compared and modulation technology adopted to the co-phase traction power supply system is analysed.Due to a great deal of switching devices in the system,device fault may be detrimental to the reliability of power supply.In multi-module convertors,redundant modules can be installed.Via cutting off redundant modules,it will keep the convertor operating normally.Secondly,a detection method based on neural network is propounded,using Fourier function,the voltage signals of characteristic harmonics and phase are selected as feature vectors.By analysing fault samples,3-layer BP neural network can be set up.After feature vectors being input into the neural network,fault diagnosis results can be got to test the accuracy of the fault diagnosis method by simulation.According to the relationship between the modulation technology and output harmonic characteristics,combining with the content of fault diagnosis,in this thesis a bypass scheme and restructuring modulation technology aimed at neutral-point-clamped(NPC)single-phase cascaded inverter are proposed.By removing redundant modules,the convertor can operate under faulty condition and keep good harmonic performance.With the MATLAB/Simulink software,a 4-module cascaded inverter simulation platform including fault diagnosis and system reconfiguration was built.The validity of the method was verified by the results of the simulation.In this simulation,the fault can be diagnosed in real time and satisfied control characteristics.Finally,by designing the circuit and controller parameters,a small power experiment based on 3-H bridge cascaded inverter was carried out.The experimental results prove the validity of the control strategy.