Reliability Assessment Of IGBT Performance Degradation Characteristic Parameters Based On Accelerated Aging Test

IGBT module is widely used in power converter with the advantages of high input impedance and low conduction voltage drop.It is one of the most core devices in converter and also one of the most vulnerable devices.Reliability assessment of IGBT module is of great significance for the reliable operation of converter.The existing reliability assessment methods of IGBT modules are mostly based on the traditional reliability theory.On the one hand,it takes much time to collect the failure time of IGBT module which operate in actual converter,and then according to the judgment criteria of probability and statistics,the appropriate probability and statistics distribution model is selected to fit the failure data to obtain the reliability model and life distribution model of IGBT module.On the other hand,another reliability assessment method is to obtain the relationship model between IGBT module life and stress through accelerated aging test,and then uses extrapolation method to analyze the reliability of modules working under normal stress.In the practical application of those methods,it is too difficult to collect a lot of failure time data because many countries and regions of wind power development time is short,and real work environment of IGBT module is complicated,various factors cause the IGBT module failure together,using the life and stress relationship model obtained by accelerated aging test to assess the reliability of IGBT module is extremely difficult,which lead the reliability assessment results differ greatly from the actual situation.Due to the inevitable irreversible changes of materials and structure inside the module during the fatigue failure process of IGBT module,the electrical parameters of the module port will be offset,and the health status of IGBT module can be reflected by monitoring the electrical parameters of the module port.For this reason,this paper proposed a reliability assessment method based on IGBT module performance degradation characteristic parameters.Since the change of characteristic parameters can directly reflect the health status of IGBT module,it does not need to analyze the stress and operating conditions of the module,so this method is more direct and applicable to a wider range.The main contents of this paper are as follows:Firstly,the failure mechanism and failure characteristics of IGBT module are analyzed,and the electrical characteristic parameters of an IGBT module port are selected as the characteristic parameters of module performance degradation.Considering the advantages of high saturation voltage drop identification,easy to measure and reflecting the aging process of IGBT module,the collector-to-emitter saturation voltage drop was selected as the degradation characteristic parameter for reliability evaluation.Because the performance characteristics of IGBT module are affected by both aging and temperature,it is difficult to ensure the accuracy of temperature in actual measurement.Therefore,a method is adopted to measure the saturation voltage drop at a specific collector current.The saturation voltage drop of IGBT module under the current is not affected by temperature,which can accurately reflect the health status of IGBT module.Secondly,in the actual operation process,it is difficult to extract IGBT module performance degradation parameters,which caused failure data accumulation less.This paper intends to obtain IGBT module degradation characteristic parameters rapidly through accelerated aging test.Therefore,this paper builds a power cycle DC accelerated aging test platform with junction temperature as the control variable,and designs a saturation voltage drop online acquisition system according to the principle of unsaturated protection circuit of IGBT module to obtain the variation of saturation voltage drop during the aging process.In order to ensure the accuracy of characteristic parameter acquisition,an off-line saturation voltage drop acquisition system was designed.By measuring the output characteristic curve of IGBT module,the saturation voltage drop under specific collector current was extracted as the characteristic parameter of reliability assessment.Based on the accelerated aging test platform,the accelerated aging test was conducted on the IGBT module 2MBI175VA-120-50 produced by Fuji electric,and the degradation information of saturated voltage drop was obtained.Finally,the reliability assessment principle based on performance degradation characteristic parameters is introduced.Considering the Wiener process can describe the difference of product materials and structure very well.Therefore,the IGBT module reliability analysis is modeled by using the Wiener process,and the corresponding evaluation results can be obtained.Moreover,compared with the reliability evaluation results based on the traditional failure time method,the reliability evaluation results based on using the degraded data can more accurately evaluate the reliability of the IGBT module,solve the traditional restricted use of reliability evaluation methods problem,which is caused by the lack of failure time in the actual process,and verify the feasibility of this evaluation method.