Study On Optimization Method Of Frequency Conversion Control For Co-phase Power Supply Device Based On Reliability Constraint

The co-phase power supply system can effectively solve the problem of neutral-section passing and the power quality problem with negative sequence in the electrified railway,which is conducive to the development of high-speed passenger transportation and heavy freight transportation of the electrified railway.With the gradual engineering realization of co-phase power supply technology,its reliability has been paid more and more attention.In order to ensure the safe and reliable operation of the co-phase power supply system,as the core equipment of the system,the reliability optimization research of the co-phase power supply device is crucial.(1)Taking the IGBT module as the core,the reliability influence mechanism of the cophase power supply device is studied.Taking into account the random fluctuation and impact of the traction load,the reliability evaluation method based on the physical failure mechanism was selected to analyze the physical failure process of the IGBT module.Through the establishment of loss calculation model,thermal network model,junction temperature calculation model and life prediction model,etc.,the reliability of IGBT module was evaluated.The influence factors of IGBT module reliability were studied,the influence of switching frequency and power factor on reliability was compared and analyzed,and the core control parameters of reliability optimization of co-phase power supply with switching frequency were determined.(2)In order to ensure the output waveform quality of the co-phase power supply device,the harmonic analysis models of the co-phase power supply device were established.Using the three-dimensional geometric model and double fourier transform to analyze the PWM waveform,the harmonic expression of the unit module converter is derived.Based on the special topology of the co-phase power supply device and the characteristics of the carrier phase shift control,the harmonic models of the grid-side converter and the traction-side converter of the co-phase power supply device are established respectively.The minimum allowable value of the switching frequency of the co-phase power supply device was calculated by constraining the total current harmonic distortion rate specified in the technical indicators of the co-phase power supply device.(3)In order to optimize the reliability of the co-phase power supply device,a dynamic frequency conversion control strategy is proposed.The influence of the average and fluctuation of junction temperature on the life of IGBT module during thermal cycle is analyzed.In order to smooth the junction temperature fluctuation and reduce the failure rate,a dynamic frequency conversion control method is proposed.Based on the IGBT module loss and the quality limitation of the output waveform of the co-phase power supply device,the adjustable range of the switching frequency is studied.Considering the constraints of device reliability and heat dissipation,an optimized model of dynamic frequency conversion control strategy was established,and the best strategy was determined.This method effectively improves the reliability of the co-phase power supply device and provides reference opinions for the design and improvement of the co-phase power supply device.