Study On Reliability Comprehensive Test Of IGBT Module Based On Its Generalized Port Characteristics

Reliability and service life prediction of power converters has gradually become a research hotspot in recent years.The insulated gate bipolar transistor(IGBT) is subject to the thermal-mechanical stress impact during the general operation. And due to its multi- layer package structure, package failures are prone to occur,especially in the new energy grid, electric vehicle driving, electric locomotive traction, and other fields. The primary cause of its relatively low reliability is that it processes large-scale stochastic volatility power during long term. In order to avoid the package failures of IGBT modules leading to serious accidents, the relevant study on the ascendant.The transient overvoltage, overcurrent, electrical over stress and some other transient failures caused by accidental factors are time short and belong to protection. They are not the focus of reliability and life study. Therefore, to explore the reliability test and life assessment method of IGBT module, in this thesis, a series of research work is carried out around the characteristic of IGBT module in the power converter. And the corresponding experimental conclusions are obtained.Theoretical design life of IGBT is more than 30 years. In order to assess its reliability and service life, according to the existing studies, accelerate degradation test(ADT) is the common method to get amount of sample data within a short period. According to the existing experimental schemes limitations such as low efficiency and bad test data consistency, an optimized power cycling(PC) test scheme to accelerate failures of IGBT module is developed.The scheme is based on the failure mechanism of power loss lead to temperature gradient. Power devices failures are induced by thermal–mechanical fatigue in the long time operation. And the failures can be simulated and accelerated by PC test. To realize batch test, a circuit topology and control strategy of single source and multi-device under test(DUT) is developed. And it is capable of controlling the accelerated stress of power-cycling aging test system effectively and accurately.Based on the analysis of port thermal characteristics of IGBT module, a method used to control and optimize power cycle rate is developed. The existing service life models suggest that junction temperature fluctuations(?Tj) and rate in the power–cycling are the key factors affecting the number of power cycles. Therefore, in this thesis, based on the electro-thermal analogy of IGBT thermal characteristics, each power cycle is equivalent to the complete response and zero-input response of RC thermal network. Besides, the coupled thermal impedance is difficult to extract in the existing thermal network model. Aiming at this problem, this thesis presents a new extraction method of discrete square wave. Thus a complete integrated power cycle thermal network numerical calculation model is established. By experiments verification, the model can be not only used to optimize power-cycling rate, but also to lay a theoretical and experimental foundation for follow-up reliability study on the thermal network.For the purpose of DUT status monitoring and aging data effective extraction, a set of automatic and multifunctional extractionunit is designed. The unit can extract multiple port parameters of IGBT module. The unit is with the priorities of high efficiency, free from human disturbance and damage during the test. Besides, the unit makes full use of IGBT module external port for monitoring and extraction. Therefore, it is applicable to conventional package module, decapsulation of module can be avoided, and the experimental results are more realistic. A solid foundation for further research on on-line monitoring is laid.Finally,in accordance with the proposed optimization design scheme, a comprehensive power cycling reliability test prototype is constructed. A batch of IGBT is test. And based on the monitoring of the port parameters of modules, a preliminary analysis on the DUT is made. Analysis results show that the proposed reliability test method is effective and can be used as a comprehensive and basic test platform for further power-cycling test and aging characteristics parameters study.