Study On Some Issues Of Fault Detection,Tolerance,and Lifetime Prediction Of The Traction Power Converter

It is of importance to ensure the stable and safe operation of the high-speed chain.As is one of the key components of the high-speed chain,the traction converter plays a vital role in the reliability of the safety of the train.Besides,according to an industry-based survey,the power device is the weakest component in power converters.Therefore,by means of fault detection,fault tolerance and predictive maintenance,the reliable operation of power module can be ensured,which has significant practical significance for improving its operation reliability,reducing maintenance costs and fault influences.In this paper,the two-level traction inverter of electric multiple units is taken as the research object,and the main objective is to improve the operation reliability of traction inverter.The detection method of the open-switch fault of insulated gate bipolar transistors(IGBTs)of traction inverters,the fault-tolerant scheme,and the life prediction method of power devices under variable working conditions are studied in this paper.The specific research contents are as follows.Firstly,considering that the open-switch fault of IGBTs in traction inverters will produce additional fault frequency components in the stator current of traction motor,wavelet packet decomposition-and ensemble empirical mode decomposition(EEMD)-based Shannon entropy and Tsallis entropy are used to detect this kind of fault.The detection effectiveness evaluation factor ? is defined to evaluate the detection stability of different algorithms.It turns out that Tsallis wavelet packet energy entropy is the best fault detection algorithm of all the above.Besides,as energy entropy cannot locate the faulty IGBT,the DC component of the faulty phase current is added to the algorithm to locate the fault.The hardware-in-the-loop(HIL)tests verified that the proposed method can detect and locate the faulty IGBT under dynamic and different working conditions.Secondly,considering the complexity of TWPEE calculation,it is difficult to realize the real-time detection of IGBT fault in the traction control unit.Therefore,a phase voltage residual-based open-switch fault detection algorithm is proposed.With the comprehensive switching function,the performance of phase voltage in the normal and faulty conditions is analyzed and the residual is obtained.Based on the analysis,its performance under different faults is obtained,by which the theoretical residual value and fault detection time are derived and the criterion for the fault detection and localization can be known.The residuals come from the switching function and the back electromotive force,which reduces the hardware costs.Besides,normalization is adopted for the residual,ensuring its ability to work under different conditions.Finally,HIL tests are carried out to verify that the proposed method can diagnose the open-switch fault of the traction inverter within one fundamental period,under different motor speeds and load toques,without additional hardware.Next,a current residual vector-based open-switch fault detection method for traction rectifier has been proposed.By analyzing the current path under faulty conditions,the reason for the indistinguishability of diagonal switch faults has been revealed.The fault current observers are established by introducing the switching system model,which includes the control sequence information.Then,the current residual vector is obtained.According to the behaviors of the elements in the current residual vector,the faulty IGBT can be detected and located correctly.The RT-LAB platform is utilized to validate the proposed method.Results show that the faulty IGBT can be diagnosed correctly under different working conditions,without additional hardware.Then,for the existing three-phase six-switch(TPSS)fault-tolerant scheme,the IGBT without freewheeling diode has been replaced with an IGBT with a diode rectifier,so as to avoid IGBT damage caused by the high reverse voltage during operation.Besides,the modulation method under capacitor voltage fluctuation and the compensation scheme for capacitor voltage bias are given.The torque ripple of the improved TPSS scheme and threephase four-switch(TPFS)fault-tolerant scheme under different speeds and torques is analyzed.With the above analysis,a fault-tolerant strategy with low torque ripple is proposed.HIL results show that the proposed strategy can select the proper fault-tolerant topology with lower torque ripple under different working conditions,ensuring the stable continuous operation of the traction drive system.Finally,apart from the instant faults during the operation of the traction inverter,the degradation caused failures should also be considered.This kind of failure does not immediately affect the system,but it gradually degrades its performance over time,resulting in failures.Hence,aiming at the bond wire degradation in IGBT modules,the temperature distribution and the on-state voltage growth with the degration has been analysed through finite element simulation.Based on this,the state-space model of the degradation process is established,and the temperature effect and metallization degradation effect are compensated.Then,the unknown model parameters are recognized by marginalized resample-move approach(MRMA).The state particles produced by MRMA are utilized to predict the lifetime of the IGBT module.In order to validate the proposed method,a power cycling test platform is established.According to the test results,the proposed method can predict the IGBT module lifetime correctly even if the temperature swing amplitude varies.