Study On Reliability Evaluation Of Co-phase Power Supply Device And Its Improvement Measures

The power frequency single phase AC system is widely used in electrified railways in China,which cause some problems,such as power quality dominated by negative sequence and over passing phase are raised.The co-phase power supply system based on the symmetric compensation theory is an ideal solution to the problems.The co-phase power supply device is the core component of the co-phase power supply system,and its reliability evaluation is crucial to the safe operation of the co-phase power supply system.Firstly,topological structure and working characteristics of power module of co-phase power supply device is analyzed,considering the effect of power component junction temperature fluctuations caused by the randomness and impact of actual traction load,the power loss model and the thermal network model is adopted to calculate power component junction temperature.Based on the rain flow algorithm,amplitude of the average junction temperature and junction temperature fluctuation of each cycle are obtained,combined with the Coffin-Manson element failure model and accumulative linear damage model,the IGBT module failure rate is calculated.Moreover,based on the reliability model and patameters provided by reliability prediction handbook for electronic equipment,the failure rate of DC side capacitor,series reactor and control panel are calculated,thus the reliability model of the device is constructed.Secondly,the influence of failure rate of components caused by changes in the number of cascaded modules in power modules is studied,a k-out-of n:G dynamic reliability evaluation model of co-phase power supply device is built,taking the special cascade topology of co-phase power supply device of Shayu traction substation for example,based on the measured traction load,the dynamic reliability of co-phase power supply device is analyzed.With the constraint effect of reliability requirements,the influence of power module level redundancy,unit level redundancy on the reliability of the co-phase power supply are researched,and the best redundancy scheme is determined.Finally,the influence of traction load characteristics and design parameters on the reliability of co-phase power supply device is studied,including power factor,heat dissipation thermal resistance,and switching frequency etc,a frequency conversion control strategy is proposed to improve the reliability of co-phase power supply device.Taking the power module failure rate minimum as the optimization objective,the current switching points and switching frequency as optimization variables,the improved particle swarm optimization is used to get the best frequency conversion control strategy,the failure rate of power module is greatly reduced.It provides an important basis for the engineering design,operation and maintenance of the co-phase power supply system.