Research On Capacitor Parameter Monitoring And Life Prediction Of Buck Converter

Switching power supply has been widely used in communications,medical,transportation,industry and military fields because of its advantages of small loss,fast response,small size and light weight.Electrolytic capacitor is the key component of switching power supply,but it has the disadvantages of short life and easy failure,which restrict the use of switching power supply.Electrolytic capacitor failure will seriously affect the safety of switching power supply,and even cause huge economic losses,casualties.Therefore,real-time monitoring of electrolytic capacitor status changes,prediction of its remaining life for improving the reliability of switching power supply is of great significance.In this paper,the electrolytic capacitor of the Buck converter is treated as the research object,studying its work in two modes: continuous mode(Continuous Conduction Mode,CCM)and discontinuous conduction mode(Discontinuous Conduction Mode,DCM)monitoring method of capacitance parameters,and predicting its residual life.First of all,the basic principles of the structure and equivalent circuit of aluminum electrolytic capacitor are introduced.The temperature and frequency characteristics of ESR(Equivalent series resistance)and capacitance C,which are two important parameters of electrolytic capacitor,are analyzed emphatically.The main failure modes and failure mechanisms of capacitors are discussed.The main reasons causing degradation of electrolytic capacitors are described.A small signal model of continuous operation of Buck circuits is established.The influence of the degradation of aluminum electrolytic capacitor parameters on the output of Buck converter is analyzed from the point of view of transfer function.Secondly,by analyzing the operating characteristics of the buck converter in different operating modes,the real-time online calculation model of ESR and C of the Buck converter is derived according to the ripple voltage of the output capacitor and the expression of the capacitor current in the continuous conduction mode and the intermittent conduction mode,respectively.The closed-loop simulation model of Buck converter is built on the simulation platform.The simulation results show that the error of the calculation method is small and the effect is good.Taking an actual product as an example,the parameters of electrolytic capacitor are extracted more accurately,which proves the correctness and effectiveness of the method.Finally,the life prediction model of electrolytic capacitor is determined according to the trend of ESR.The remaining life of the electrolytic capacitor is predicted in short term,which is based on Support Vector Machine(SVM)and Least Square Support Vector Machine(LS-SVM).The simulation results show that both SVM and LS-SVM can effectively predict the remaining life of the electrolytic capacitor,and the prediction result based on LS-SVM is more accurate.