Research On Multiple Open-circuit Fault Diagnosis Method Of IGBTs For Two-level Traction Converter System

China’s high-speed railways have developed and increased rapidly and China has built the world’s largest and fastest operating high-speed railways mainline network.As one of the key systems in high-speed railways,the reliability of the electric traction converter is essential to the safe and stable operation of high-speed trains.The insulated gate bipolar transistor(IGBT)module,as the core component of the traction converter,has the highest failure rate in the electric traction system.Therefore,online real-time detection and accurate location of IGBT faults in traction converters are of great significance to improve the safety and reliability of high-speed trains.In this paper,two-level traction converter systems of the high-speed electric traction system are concerned as the research objects.The diagnosis algorithms for IGBT multiple open-circuit faults are studied.The specific research work is as follows.Firstly,the DC-link voltage observation model of two-level traction converter in the electric traction system is established,constructing the DC-link voltage observer based on the mixed logic dynamic model.And the accuracy of the observer under various operating conditions is verified through the simulation.Secondly,the DC-link voltage observer is used to estimate the DC-link voltage,and the measured value is compared with the estimated value to generate voltage residual.By analyzing the voltage residual under different IGBT open-circuit faults,the corresponding fault characteristics of IGBT at different positions are extracted and diagnostic variables are constructed.In order to decouple the fault characteristics when open-circuit faults occur simultaneously on the rectifier side and inverter side,auxiliary location variables are designed on both side respectively,and the fault characteristic values and fault location variables in system level are summarized for multiple IGBT open-circuit faults to provide a theoretical basis for the subsequent establishment of diagnostic rules.Then,the fault diagnosis method for multiple IGBT open circuits based on the DC-link voltage residual is proposed.The implementation process of the fault detection and location algorithm is first introduced,focusing on the hierarchical diagnostic algorithms,including the single fault diagnosis algorithm and the optimization algorithm for multiple open-circuit faults.And then,the selection of diagnostic threshold under system parameter variation is considered,and the diagnosis algorithm is extended to the two-level traction converter system considering the double pulse width modulation(PWM)rectifier structure.Finally,the proposed diagnosis method for IGBT multiple open-circuit faults is verified by the hardware-in-the-loop(HIL)test based on the real-time simulator RT-LAB and the actual controller TMS320F28335.The results show that the DC-link voltage observer can accurately estimate the DC-link voltage and the proposed methods are suitable for the electric traction system.The diagnostic method can complete the single IGBT fault detection and location of the rectifier side and the inverter side within 1/4 of the current fundamental cycle.Furthermore,multiple IGBT open circuit faults at different positions can also be diagnosed within one fundamental cycle.The proposed method is insensitive to grid voltage changes,load changes,and motor speed changes,and have good practical adaptability.