Study On Reliability Optimization Method Of Power Flow Controller For Co-phase Traction Power Supply System

The power quality issues represented by voltage unbalance and the electrical sectioning issues have severely restricted the further development of electrified railways under traditional traction power supply system(TPSS).Co-phase power supply technology can comprehensively solve the above problems,which is based on symmetrical compensation theory and high-voltage large-capacity converters.As the core component of co-phase TPSS,the reliability of power flow controller(PFC)plays a decisive role in the safe and efficient operation of co-phase TPSS.Therefore,it is necessary to study the reliability of the PFC and propose an optimization scheme to improve its reliability.Firstly,the reliability evaluation model of the PFC is established.The topology and working characteristics of the co-phase power supply system and the PFC are analyzed,based on the physical failure mechanism of the power device,the loss calculation model,junction temperature calculation model of IGBT module taken into account the random volatility of the traction load are established,and the heat sink-environmental thermal resistance is solved,the reliability evaluation process of the PFC is obtained,the effectiveness and accuracy of the evaluation process are verified through case analysis.Secondly,the factors affecting the reliability of the PFC are analyzed.Based on the thermal analysis theory,a heat dissipation simulation model of the PFC’s power device is built,and the influence of the change of external heat dissipation wind speed on the thermal coupling between power devices,the junction temperature of the power device and the heat sinkenvironment thermal resistance is analyzed;based on the influence of the reliability of the power flow controller mechanism,the influence of switching frequency and modulation mode on the reliability of the IGBT module is analyzed,and the optimal design control parameters based on the switching frequency,modulation method and heat dissipation wind speed are determined.Finally,the effects of average junction temperature and junction temperature fluctuation on the failure rate of power devices during thermal cycling are analyzed.In order to reduce junction temperature and smooth junction temperature fluctuation,a comprehensive control strategy combining control switching frequency,modulation method and heat dissipation wind speed is proposed.A comprehensive control strategy optimization model is established that takes the highest reliability of the PFC as the optimization goal,and takes the load partition point,switching frequency and heat dissipation wind speed as the optimization variables.The particle swarm algorithm with constriction e factor is used to solve the model,and the optimal control strategy is obtained to improve the lifetime of the PFC.