| Device failure is reported to be the main reason affecting the reliability of power electronic converters or systems.With a massive penetration of power electronic converters in both industrial production and daily life application,the meaning of the power module reliability scheme should be updated as it is the time to fulfill its role to realize on-line monitoring,diagnostics and prognostics,instead of being restricted within the stage of R&D.Taking the reliability scheme of IGBT modules used in electric drive system as the research target,its failure mechanism can be divided into transient failure and aging failure according to time scale.Therefore,a reasonable reliability scheme of power modules should be able to cope with both two types of failures.Compared with the transient failure which is full of contingency,the aging failure exists in the entire life cycle of the module,and it is with no doubt the key factor that influence the reliability of the module and even the converter system.The aging failure comes together with inappropriate heat management of the module.The components inside the module can be categorized into either heat source or heat dissipation path and the reasons which cause the change of heat generation and degradation of heat dissipation performance are discussed.The bond wire fatigue is the main reason leads to the increase of loss power and heat generation of the module.The IGBT equivalent circuit is used to analyze its conduction characteristics,which reveals the influence brought by the breaking and shedding of bond wires on the on-state saturation voltage drop.However,bond wire fatigue is not the only reason that affects the chip on-state saturation voltage drop.Therefore,a forward characteristic modeling of IGBT based on instantaneous on-state resistance is proposed,in order to provide a comprehensive understanding of the on-state saturation voltage drop considering the effects from collector current and junction temperature.The model can be used to judge whether the on-state saturation voltage drop deviates from its theoretical value under corresponding working conditions,which can tell if the bond wire fatigue occurs or not.The aging fatigue of solder layer leads to the increase of thermal resistance inside while the fatigue of grease impacts on the heat dissipation performance outside the module.Thermal resistance is a key parameter reflecting the status of heat dissipation ability.Since the calculation of thermal resistance inside requires the knowledge of the junction temperature and junction temperature is also of vital importance in the condition monitoring of IGBT modules,two different methods for extracting junction temperature are discussed in the paper.The thermal network-based method is firstly analyzed and validated through a PSIM-based thermal-electrical simulation platform,where the transient thermal impedance curve of the module in the datasheet is fitted by particle swarm optimization algorithm to extract the RC parameters of Foster thermal network.The simulation results are consistent with the online simulation data provided by the manufacturer and it also indicates that the change of thermal resistance on the external heat dissipation path can be reflected in the module case temperature curve.The aging effects of thermal grease on the external heat dissipation path is verified on a single-phase LCL inverter platform using SKM75GB123 D.What is more,the mechanism of Miller platform during IGBT turn-on gate voltage is analyzed and its temperature sensitivity is verified both theoretically and through a dual-pulse experiment for FF600R12ME4C_B11. |
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