A temperature gradient based Condition Estimation Method for IGBT Module

The paper presents a temperature gradient based method for device state evaluation, taking the insulated Gated Bipolar Transistor (IGBT) modules as an example investigation. Firstly, theoretical basis of this method is presented and the results from example calculation on temperature gradient indicate that the increased thermal resistance and power loss of IGBT modules would increase the temperature gradient. Then an electrical-thermal- mechanical finite element method (FEM) model of IGBT modules, which takes the material temperature-dependent characteristic into account, is utilized to estimate the temperature gradient distribution for both healthy and fatigue conditions. It is found that the temperature gradient varies with power loss. Furthermore, both the experimental and simulation investigation on the temperature gradient for different conditions were conducted, and it is concluded that the temperature gradient can not only track the change of power loss, but have a better sensitivity compared with temperature distribution. In addition, the temperature gradient can reflect the defects location and distinguish failures degree. In the end the influence on the temperature gradient distribution caused by solder fatigue, void and delamination are discussed

Enabling high reliability power modules : a multidisciplinary task

Reliability of power electronic systems is a major concern for application engineers in the automotive and power system sectors. Power electronic modules are one of the main sources of failure in wind energy conversion systems. Power electronic converters used in wind turbine electric drive trains, railway traction, more-electric-aircrafts, marine propulsion and grid connected systems like FACTS/HVDC require reliable power devices and modules. Wide bandgap semiconductors like SiC have demonstrated enlarged electrothermal Safe-Operating-Areas compared with silicon devices. However, the reliability of SiC power modules and packages has been identified as an area of potential weakness. Traditional packaging systems have been developed for Si hence the different thermomechanical properties of SiC cause different stresses in the packaging thereby potentially causing reduced reliability. This paper identifies some of the key areas for the development of reliable power electronic systems using SiC. The focus is on condition monitoring, packaging system innovation and thermomechanical stress analysis as a function of the mechanical properties of Si and SiC. Power cycling experiments and finite element models have been used to support the analysis

A leaf vein-like hierarchical silver grids transparent electrode towards high-performance flexible electrochromic smart windows

Abstract(#br)As essential components of numerous flexible and wearable optoelectronic devices, the flexible transparent conducting electrodes (TCEs) with sufficient optical transmittance and electric conductivity become more and more important. In this work, we fabricated a large-area flexible TCE based on leaf vein-like hierarchical metal grids (HMG) comprising of mesoscale “trunk” and microscale “branches”. The self-formed branched grids made the conducting paths distributing uniformly while the laser-etching trunk grids enabled to transport the collected electrons across long-distance. The Ag HMG exhibited high optical transmittance (~81%) with low sheet resistance (1.36 Ω sq –1 ), which could be simply optimized through adjusting the grids’ widths, spaces, and the sizes of the TiO 2 colloidal crackle patterns. In addition, on the basis of such advanced HMG electrode, flexible electrochromic devices (ECDs) with remarkable cyclic performance were fabricated. The HMG with high transparency, conductivity, and flexibility provides a promising TCE for the next-generation flexible and wearable optoelectronic devices

Analysis and Prediction Model of Resident Travel Satisfaction

To promote the sustainable development of urban traffic and improve resident travel satisfaction, the significant factors affecting resident travel satisfaction are analyzed in this paper. An evaluation and prediction model for travel satisfaction based on support vector machine (SVM) is constructed. First, a multinomial logit (MNL) model is constructed to reveal the impact of individual attributes, family attributes and safety hazards on resident travel satisfaction and to clarify the significant factors. Then, a travel satisfaction evaluation model based on the SVM is constructed by taking significant factors as independent variables. Finally, travel optimization measures are proposed and the SVM model is used to predict the effect. Futian Street in Futian District of Shenzhen is taken as the object to carry out specific research. The results show that the following factors have a significant effect on resident travel satisfaction: age, job, level of education, number of car, income, residential area and potential safety hazards of people, vehicles, roads, environment, etc. The model fitting accuracy is 87.76%. The implementation of travel optimization measures may increase travel satisfaction rate by 14.07%

Power Loss Prediction for Aging Characteristics and Condition Monitoring for Parallel-Connected Power Modules Using Nonlinear Autoregressive Neural Network

Power modules connected in parallel may have different electrothermal performance variances resulting from aging because of the nonuniform rate of degradation; different electrothermal performance variances mean different current sharing, different junction temperature, and power losses, which will directly influence the overall characteristics of them. Thus, it is essential to monitor the condition and evaluate the degradation grade to improve the reliability of large-scale power modules. In this paper, the impact of thermal resistance difference on current sharing, junction temperature, and power loss of parallel-connected power modules has been discussed and analyzed. Additionally, a methodology is proposed for condition monitoring and evaluation of the power modules without intruding them by recognizing the increase in external power loss due to internal degradation from aging. In this method, power modules are deemed as a whole system considering only external factors associated with them, all important electrical and thermal parameters are classified as the inputs, and power loss is considered as the output. Firstly, power dissipation is predicted by models using NARX (nonlinear autoregressive with exogenous input) neural network. Then, a monitoring method is illustrated based on the prediction model; a reasonable criterion for the error between the normal and the predicted real-time power loss is established. Finally, the real-time condition and the degradation grade of aging can be evaluated so that the operator can take suitable operating measures by means of this approach. Experimental results validated the effectiveness of the proposed methodology

A study of the permeability of fractures with variable attitude in rock mass subjected to natural crustal stresses

In order to investigate the influence of fracture attitude variation on the permeability of fractures in deep rock mass under natural crustal stresses, based on the permeability law of a single fracture obeying the law of negative exponential change, the theoretical formula of coefficient of permeability of fractures with variable attitude subjected to 3D stresses is proposed. The Lagrange multiplier method is applied to analyze the change of variable attitude on fracture permeability, and influence factors and sensibility of fracture permeability with or without infillings are also analyzed. Statistic law of crustal stress in Chinese mainland is taken as an example, and the variable laws of the permeability of fractures in rock mass with depth and fracture attitude are analyzed. The results show that (1) the permeability of fractures in rock mass is obviously influenced by the attitude of fractures. For shallow rock mass, under the condition of the maximum principle stress distribution in the horizontal direction, the permeability of fractures gradually decreases with the increasing dip angle of fractures; but with the increasing depth, when the depth is more than 200 m and the strike of fracture is roughly consistent with the direction of large or medium principal stress, the permeability of fractures can increase with the increasing dip angle of fractures, especially the strike of fractures perpendicular to the direction of the minimum principle stress. For deep rock mass, the permeability of fracture is very weak, and the impact of fracture attitude change on its permeability is very slight. (2) For fractures with infillings, the change of elastic modulus ratio of rock block to infillings and Poisson’s ratio of infillings have little effect on fracture permeability. The conclusions can be used for reference for further investigating the variation of deep rock permeability characteristics

Study on the lifetime characteristics of power modules under power cycling conditions

This study presents a study on non-linear accumulative modelling for power module lifetime estimation in non-accelerated operation. The model focuses on solder fatigue based on monitoring the internal thermal resistance of the module. Initially, the relatively small junction temperature variation (ΔTj) cycles contribute little to the lifetime consumption, but with an initial damage the effect becomes noticeable. The original Coffin-Manson accumulation approach is extended for complex mission profiles. The proposed non-linear accumulation model has three aspects: a Coffin-Manson relationship is first established; the thermal resistance degradation is then used to quantify damage accumulation; the effects of the average junction temperature (Tjmean) and ΔTj on the rate of degradation are finally included through the parameters of the non-linear accumulation model which also depends on the effect of the present condition of the module. Experiments demonstrate the phenomena and verify the proposed model

Low ΔTj stress cycle effects in IGBT power module die-attach lifetime modelling

Operational management for reliability of power electronic converters requires sensitive condition monitoring and accurate lifetime modeling. This study adds to the second aspect by examining the effect of cyclic junction temperature variations (ΔTj) of low amplitude in different stages of the power module ageing process. It is found that such relatively minor stress cycles, which happen frequently during normal operation, may not be able to directly initiate a crack but can contribute to the development of damage due to stress concentration. This agrees with the observation that the ageing process tends to accelerate towards the end of life. The study investigates the dependency of the ageing effect on the amplitude of ΔTj, the mean junction temperature Tm and the present health condition of the module, and proposes a lifetime model focusing on die-attach solder fatigue. It is assumed that the future ageing process is independent of the operational history that has led to the current state of health. The model is intended for operational management of converter systems that are subject to frequent low ΔTj stress cycles and are supposed to be in service reliably for a long time with a slow ageing process. Experimental results validate the model