Mission Profile Based Reliability Assessment And Optimization Design Of Switching Mode Power Supply

The switching mode power supply(SMPS)has been widely used in ae rospace,national defense,electrical transportation,renewable energy and other industial applications.Highly reliable SMPSs are the premise for a reliable operation of the entire system.Facing the complex and various operating conditions,how to evaluate and optimize the reliability of SMPS in the stage of design and prototype is a critical problem concerned by both manufacturers and researchers.At present,the electro-thermal simulation of SMPS can not accurately analyze the component stresses under various mission profiles of SMPS.The lifetime prediction method is lack of consideration of mission profiles.The reliability model of SMPS neglects the performance degradation and uncertain factors.The reliability optimization design method does not consider the robustness and reliability of SMPS comprehensively.These problems lead to the deviation between the reliability assessment results and the pratical situations.Additionally,the lifecycle reliability of SMPS cannot be solved at the design stage.To solve mentioned problems,this paper studies the reliability assessment and optimization design method of SMPS considering its mission profile.Based on a multi timescale electro-thermal simulation model,the variations of mission profile is transformed into stress changes of reliability-critical components such as MOSFETs and aluminum electrolytic capacitors(Al-Caps).And then,the component lifetime is predicted based on cumulative damage model.Afterwards,the system reliability model of SMPS considering degradation is established.The influence of uncertainty factors such as component tolerance,parameter degradation and mission profile on the system reliability is analyzed.Finally,reliability-oriented robust optimization design is carried out based on reliability assessment results.Firstly,in order to evaluate the electrical-thermal stresses of reliability-critical components,a multi timescale electro-thermal coupling simulation method is proposed.For the components with highest historical failure rate,MOSFETs and Al-Caps,the dynamic switching characteristics of MOSFET are analyzed,and the transient thermal simulation model of MOSFET's junction temperature is established.The electrical parameters of Al-Cap under various conditions are analysed and modeled.A thermal simulation model of Al-Cap's core temperature is established.The circuit simulation and thermal simulation of SMPS are established in Saber and ANSYS Icepak,respectively.The simulation control and data interaction are realized based on the i SIGHT platform.The electrical and thermal characteristics of SMPS under different working conditions are analyzed,which lays the foundation for the lifetime prediction and reliability assessment of SMPS.Secondly,in order to predict lifetime of reliability-critical components,a lifetime prediction method based on the mission profile of SMPS is proposed.The failure mechanisms of MOSFETs and Al-Caps operating in SMPS are analyzed.The accelerated life models of key components are established based on the accelerated testing.The fatigue accumulation rules of MOSFETs and Al-Caps are analyzed,and the cumulative damage models under time-varying stress are established.The electrical and thermal stresses of MOSFETs and Al-Caps under mission profle are analyzed by the multi timescale electro-thermal simulation model of SMPS.The results are substituted into accelerated life model and cumulative damage model to predict the lifetime of MOSFET and Al-Cap.Thirdly,the reliability assessment method of SMPS based on degradation is proposed.The reliability model of SMPS is established from the two aspects,i.e.,component degradation failure and performance degradation.The relationship between component degradation model and reliability is deduced,and the reliability model of SMPS based on limit state equation is established.Based on the results of component life prediction,a parameter degradation model based on time-varying distribution is established for AL-Caps,which is regarded as the short life plate in SMPS.The acceleration effect of parameter degradation on self electrothermal stresses is analyzed.By the Monte Carlo simulation method,random samples are generated to assess the reliability of SMPS considering the degradation failure of Al-Caps.For the degradation of the performance of SMPS,the performance sensitivity analysis method is studied,and the sensitive parameters that cause the performance fluctuation are determined.The radial basis approximation model for fast calculation of the SMPS performance is established.The reliability of SMPS is evaluated with the parameter degradation model of sensitive devices.Finally,the reliability robust optimization design methods for SMPS are proposed to optimize the robusteness and reliability of SMPS synchronously.The lifecycle robustness and reliability of SMPS are improved from two aspects: the precentile life of components and the performance degradation of SMPS.For the percentile lifetime of Al-Cap,a robust design optimization model based on the consistency of percentile lifetime is established.The parameters and tolerances of Al-Cap are optimized by particle swarm optimization(PSO)to improve its lifetime as well as reduce the sensitivity of percentile lifetime to the mission profile.F or the performance reliability,a lifecycle-cost based robust design model is established.The tolerance of sensitive components is optimized by multi-objective genetic evolutionary algorithm to improve the performance reliability during the lifecycle of SMPS.