Modeling of Sic Power Semiconductor Devices For Switching Converter Applications

Thanks to recent progress in SiC technology, SiC JFETs, MOSFETs and Schottky diodes are now commercially available from several manufactories such as Cree, GeneSiC and Infineon. SiC devices hold the promise of faster switching speed compared to Si devices, which can lead to superior converter performance, because the converter can operate at higher switching frequencies with acceptable switching losses, so that passive filter size is reduced. However, the ultimate achievable switching speed is determined not only by internal semiconductor device physics, but also by circuit parasitic elements. Therefore, in order to accurately predict switching losses and actual switching waveforms, including overshoot and ringing, accurate models are needed not only for the semiconductor devices, but also for the circuit parasitics. In this dissertation, a new physics-based model accounting for non-uniform current distribution in JFET region for the power SiC DMOSFET is presented. Finite element simulation shows that current saturation for typical device geometry is due to two-dimensional (2-D) carrier distribution effects in JFET region caused by current spreading from the channel to the JFET region. Based on this phenomenon, a new model is proposed that represents the non-uniform current distribution in the JFET region using a non-linear voltage source and a resistance network. Advantages of the proposed model are that a single set of equations describes operation in both the linear and saturation regions, and that it provides a more physical description of MOSFET operation. The model represents an original contribution in the area of physics-based power semiconductor device modeling. This model is validated both statically and under resistive conditions for SiC DMOSFET showing overall good matching with experimental results and finite element simulations. This dissertation also presents a simple physics-based power Schottky diode model which is comprised of a voltage controlled current source, a temperature dependent drift region resistance and a nonlinear capacitance. A detailed parameter extraction procedure for this model is also discussed in this work. The developed procedure includes the extraction of doping concentration, active area and thickness of drift region, which are needed in the power Schottky diode model. The main advantage is that the developed procedure does not require any knowledge of device fabrication, which is usually not available to circuit designers. The only measurements required for the parameter extraction are a simple static I-V characterization and C-V measurements. Furthermore, the physics-based SiC Schottky diode model is also temperature dependent and is generally applicable to SiC Schottky diodes. This procedure is demonstrated for four different Schottky diodes from two different manufacturers. The parameter extraction procedure represents an original contribution in the area of characterization of power semiconductor devices. In order to capture the parasitic ringing in the very fast switching transients, a procedure to accurately model circuit parasitics is also presented. A double pulse test-bench was built to characterize the resistive and inductive switching behavior of the SiC devices. The parasitic inductances for resistive and inductive switching of SiC devices in this switching test circuit were modeled and analyzed using a three-dimensional (3-D) inductance extraction program. The gate-to-source switching loop and drain-to-source switching loop parasitic inductances of the PCB layout are extracted and simulated together with previously developed power SiC device models in Pspice. Simulation results show good agreement with experimental results under both resistive and inductive switching conditions

Stress Physiology and Behavior Problems

Understanding childhood externalizing problems is informative in designing interventions and reducing crime in adulthood because childhood aggression is one of the best predictors for later antisocial behavior. Childhood externalizing problems are typically studied with internalizing problems (e.g., anxiety) given their consistent correlation and seemingly opposite behavior manifestations. This dissertation examined both spectrums of behavior problems to advance our etiological understanding. Adversity and stress have been a focus in criminology research but few studies have incorporated stress physiology, the biological underpinning of how individuals deal with adversity. This dissertation comprised three papers testing the linkage of stress physiology to behavior problems. I examined how the two components of the stress system, namely the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS), interact with each other, and together interact with harsh discipline in influencing externalizing and internalizing problems. Data were drawn from a community sample of 11-12 year old children (N = 446). Saliva samples were collected in the initial assessment and later assayed for cortisol (HPA) and salivary alpha-amylase (sAA; ANS). Participants and their caregivers completed questionnaires for child behavior problems initially, 3, 6, and 12 months later. Paper 1 revealed that cortisol was negatively associated with externalizing and internalizing problems but only at low levels of sAA. Paper 2 built on Paper 1 by including harsh discipline as an environmental factor and testing how the combined effect of cortisol and sAA contributed to our understanding of the heterogeneous effect of harsh discipline on behavior problems. Results showed that asymmetry in cortisol and sAA may indicate biological susceptibility to the effect of harsh discipline to develop both externalizing and internalizing problems among boys. Given the similar stress physiological patterns shown in Paper 1 and 2 for externalizing and internalizing problems, Paper 3 further explored and found that the interplay of cortisol and sAA differentiated co-occurrence of behavior problems from other developmental trajectories of behavior problems over a year. Together these findings underscore the significance of stress physiology in behavior problems. Theoretical implications in relation to differential susceptibility hypothesis and practical implications for treatment evaluation and research are discussed

Open Access

Global spatiotemporal and genetic footprint o

A New Method of Detecting and Interrupting High Impedance Faults by Specifying the Z-Source Breaker in DC Power Networks

High impedance faults (HIFs) that cause a relatively smaller current magnitude compared to the traditional low impedance faults are not easily detectable but can cause an extreme threat to electric apparatus and system operation. This paper introduces a new method of detecting and interrupting HIFs in DC power networks by specifying Z-source circuit breakers (ZCBs). The ZCB is a protective device for high power DC branches, with the capabilities of protecting bidirectional power flow and automatic/controllable turnoff function. In this new method, the operational mode of ZCB (i.e., either the detection mode or interruption mode) can be specified. Beyond previous research, the theoretical analysis has been performed on this method and the mathematical relationship between the maximum HIF resistance and required Z-source capacitance has been derived and verified. It has been found that the ZCB can respond to a HIF accordingly when its capacitances are properly adjusted in the ZCB circuit. With the adjustment of these Z-source capacitances, the ZCB can be specified to detect and report a HIF status to power system operators, or cut off the HIF branch and protect the rest of the DC system directly. The new method can detect/interrupt a HIF that is as small as 2 times of its nominal rated current and the effectiveness and general usage of the derived equation have been verified by both low power experiments in lab and high power simulation tests

Fabricaiton and Characterization of Waveguide Structures in Transparent Optical Materials

Tesis Doctoral inédita cotutelada por la Shandong University de China y la Universidad Autónoma de Madrid. Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 31-03-201

CD2^2: Fine-grained 3D Mesh Reconstruction with Twice Chamfer Distance

Monocular 3D reconstruction is to reconstruct the shape of object and its other information from a single RGB image. In 3D reconstruction, polygon mesh, with detailed surface information and low computational cost, is the most prevalent expression form obtained from deep learning models. However, the state-of-the-art schemes fail to directly generate well-structured meshes, and most of meshes have two severe problems Vertices Clustering (VC) and Illegal Twist (IT). By diving into the mesh deformation process, we pinpoint that the inappropriate usage of Chamfer Distance (CD) loss is the root causes of VC and IT problems in the training of deep learning model. In this paper, we initially demonstrate these two problems induced by CD loss with visual examples and quantitative analyses. Then, we propose a fine-grained reconstruction method CD$^2$ by employing Chamfer distance twice to perform a plausible and adaptive deformation. Extensive experiments on two 3D datasets and comparisons with five latest schemes demonstrate that our CD$^2$ directly generates well-structured meshes and outperforms others by alleviating VC and IT problems.Comment: under major review in TOM

Passively Q-switched Nd:YVO4 waveguide laser using graphene as a saturable absorber

We report on passively Q-switched lasers in femtosecond laser written waveguide in Nd:YVO4 crystal. Using graphene as a saturable absorber, passively Q-switched waveguide laser operations are achieved along both TE and TM polarizations with single modal profiles. Furthermore, all-angle linear light pump was utilized to investigate the thorough information of the polarization effects of the laser, showing that the optimum polarization for laser generation is TE. The maximum average output power is estimated to be 129 mW with 12.2% slope efficiency, corresponding to single-pulse energy of 8.1 nJ, pulse duration of 25.0 ns and repetition rate of 16.3 MHz.This work was supported by the National Natural Science Foundation of China (No. 11274203) and Ministerio de Economía y Competitividad under Project FIS2013-44174-P, Spain

Spatial-Aware Multi-Level Parsing Network for Human-Object Interaction

Human-Object Interaction (HOI) detection focuses on human-centered visual relationship detection, which is a challenging task due to the complexity and diversity of image content. Unlike most recent HOI detection works that only rely on paired instance-level information in the union range, our proposed Spatial-aware Multilevel Parsing Network (SMPNet) uses a multi-level information detection strategy, including instance-level visual features of detected human-object pair, part-level related features of the human body, and scene-level features extracted by the graph neural network. After fusing the three levels of features, the HOI relationship is predicted. We validate our method on two public datasets, V-COCO and HICO-DET. Compared with prior works, our proposed method achieves the state-of-the-art results on both datasets in terms of mAProle, which demonstrates the effectiveness of our proposed multi-level information detection strategy