Lifetime Prediction And Reliability Research Of Aluminum Electrolytic Capacitor Based On Charging Module Task Profile

As the basic supporting facilities of electric vehicles(EV),improving the safety of charging equipment and the reliability of maintenance is an effective way to promote the market potential of EV industry.Aluminum electrolytic capacitor(Al-caps)is usually connected to the DC side of the charging module to balance the instantaneous power and improve the power quality.It is an essential part of the charging device.However,Al-caps is also one of the components with the highest failure rate in the charging module,which is an important factor affecting the system lifetime.It can be seen that lifetime prediction of DC bus capacitors in EV charging equipment is an effective means of reliability evaluation,which is crucial for the operation and maintenance of EV charging equipment.With the DC bus capacitor of VIENNA rectifier,this paper discusses the improvement of hotspot temperature calculation method and lifetime prediction method of Alcaps to improve the accuracy of hotspot temperature calculation and lifetime prediction method,and verifies the effectiveness of the proposed method with the annual profile of 30 k W EV charging module.The main work of this paper is as follows:Firstly,the working principle of the VIENNA rectifier is systematically introduced,the calculation method of the electric stress of the DC bus capacitor of the VIENNA rectifier has been studied,and the appropriate DC bus capacitor type of EV charging module is selected and the DC bus capacitor bank is designed by comprehensively considering the capacitor type,rated voltage,rated current,capacitance value and other factors.The simulation model has been built to verify the accuracy of the calculation results of electrical stress,which lays a theoretical foundation for the calculation of DC busbar capacitor hotspot temperature and lifetime prediction.Secondly,in order to solve the problem that the current capacitor power loss model ignores the frequency characteristics of ESR,the failure mechanism and failure mode of Al-caps are analyzed,the basis for capacitor failure has been summarized,and the equivalent circuit model of Al-caps has been established to analyze the influence of temperature,frequency,wear and aging on the main electrical parameters.Frequency coefficient has been introduced to describe the effect of different frequency current components on capacitor power loss.Then,considering the influence of the radiator or other heat dissipation measures on the capacitor hotspot temperature,the capacitance equivalent heating model considering the influence of heat dissipation conditions has been constructed,and the radiator wind speed-thermal resistance model has been constructed.A hotspot temperature calculation method has been proposed which comprehensively considered the ripple current amplitude-frequency characteristics and the influence of heat dissipation conditions on the capacitor heat production and conduction.The electric heating stress of DC bus capacitance under the working condition of EV charging module has been calculated,and the accuracy of the proposed method is compared with that of traditional hotspot temperature calculation method,which lays a foundation for the lifetime prediction and reliability design of EV charging equipment.Finally,the lifetime prediction and reliability analysis method of Al-caps based on the task profile has been proposed.Combined with the three-dimensional data fitting method,the voltage correction coefficient has been introduced to construct the multi-component lifetime model of Al-caps,which greatly improves the prediction accuracy of the model.Combined with the linear cumulative damage theory,the annual profile of 30 k W EV charging module was taken as an example.Real-time calculation of Al-caps lifetime under multiple task profiles in EV charging modules provides theoretical guidance for the actual operation and maintenance of EV charging modules.