Study On Coordinated Control Strategy For Parallel PFC With Reliability Restriction

To solve the problem of electrical energy quality and electrical phase in traditional traction system,the co-phase power supply system is proposed,which adopts symmetric compensation theory and high voltage large-capacity variable flow technology.As the core device of the co-phase power supply system,the reliability of power flow controller is significant to the safety and efficient operation of the co-phase power supply system.Owing to the capacity limitation of power semiconductor,multiple parallel connection of controllers has been encouraged which usually adopts average current sharing control strategy.Moreover,the system reliability can be improved by configuring redundant units.It is significant to determine the optimal redundant configuration structure of the power flow controller and mitigate the contradiction between reliability improvement and the required cost.In addition,aiming at the problem of thermal stress of power modules under average current sharing control strategy,the system reliability can be effectively improved by optimizing its control strategy.Therefore,related research is significant.First,the reliability estimation model of the power flow controller is established.The topology and operation characteristics of the co-phase power supply system and the power flow controller are analyzed.Based on the physical failure mechanism of power electronics,the power loss calculation model,the junction temperature calculation model and the randomized thermal load statistical model of the IGBT module are established.Moreover,the impact of the average junction temperature and the junction temperature fluctuation of the IGBT module on its failure rate have been studied.The reliability estimation process of the power flow controller is constructed,and the effectiveness and accuracy of the reliability estimation model has been verified by example analysis.Second,the life cycle cost model of the power flow controller is established.Based on the life cycle cost theory,the cost model of the power flow controller has been proposed,which takes the system reliability into consideration.Based on the operating characteristics of the power electronics,the influence of the redundancy of IGBT module and the power flow controllers,and the number of PFC units operating under different load conditions on system reliability and total cost are analyzed.In addition,the redundant configuration scheme of the power flow controller with reliability restriction is proposed to effectively reduce the system total cost.Finally,the optimization control strategy of the power flow controller is studied.Based on the impact mechanism of reliability and system operating characteristics,the coordination control strategy is proposed to improve system thermal stress and smooth the junction temperature fluctuations.With the constraints of negative compensation,under high load,all of the PFC units are operated simultaneously,while under low load,the units are operated by turns.Moreover,to ensure consistent reliability and maximize system reliability,the rotation working time of each unit and the load demarcation point are optimized.Finally,the effectiveness of the above strategy is verified by case studies to prove that it can efficiently improve system reliability and reduce the life cycle cost,which provides an important reference for optimal design of the power flow controller.