Browsing by Author "Wang, Jun"

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    Ambient ammonia synthesis via palladium-catalyzed electrohydrogenation of dinitrogen at low overpotential
    Wang, Jun; Yu, Liang; Hu, Lin; Chen, Gang; Xin, Hongliang; Feng, Xiaofeng (Springer Nature, 2018-05-15)
    Electrochemical reduction of N2 to NH3 provides an alternative to the Haber−Bosch process for sustainable, distributed production of NH3 when powered by renewable electricity. However, the development of such process has been impeded by the lack of efficient electrocatalysts for N2 reduction. Here we report efficient electroreduction of N2 to NH3 on palladium nanoparticles in phosphate buffer solution under ambient conditions, which exhibits high activity and selectivity with an NH3 yield rate of ~4.5 μg mg−1Pd h−1 and a Faradaic efficiency of 8.2% at 0.1 V vs. the reversible hydrogen electrode (corresponding to a low overpotential of 56 mV), outperforming other catalysts including gold and platinum. Density functional theory calculations suggest that the unique activity of palladium originates from its balanced hydrogen evolution activity and the Grotthuss-like hydride transfer mechanism on α-palladium hydride that lowers the free energy barrier of N2 hydrogenation to *N2H, the rate-limiting step for NH3 electrosynthesis.
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    Circulating current injection control
    (United States Patent and Trademark Office, 2018-12-11)
    In one example, a power converter includes a modular multilevel converter (MMC) electrically coupled between a first power system and a second power system. The MMC includes an arrangement of switching submodules, and the switching submodules include an arrangement of switching power transistors and capacitors. The MMC also includes a controller configured to inject a common mode frequency signal into a circulating current control loop. The circulating current control loop is relied upon to reduce at least one low frequency component in power used for charging the capacitors in the switching submodules. By injecting the common mode frequency signal into the circulating current control loop, the switching submodules can be switched at higher frequencies, the capacitances of the capacitors in the MMC can be reduced, and the power density of the MMC can be increased.
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    Computational Study of Parameters Affecting Electric Cabinet Fire Heat Release Rate
    Salvi, Urvin Uday (Virginia Tech, 2022-06-22)
    Electrical cabinet fires occur frequently in commercial and industrial facilities. However, the severity of these fire events varies widely, making it difficult to estimate the fire growth and size with certainty. This study aims to identify the significant parameters that affect electrical cabinet fires, which are quantified as the heat release rate (HRR), and properly categorize them. With this knowledge, optimal parameter-response relationships can be developed to predict the electrical cabinet fire behavior. Statistical analysis conducted in this study on historical fire incident data revealed that the fires in Nuclear Power Plants (NPP) were primarily associated with electrical cabinets. The database used in this research was an electronic version of the publicly available Updated Fire Event Database developed by Electric Power Research Institute, including 2,111 fire events. 540 of these events were labeled as being challenging fires with 74.2% of these challenging fire events being due to eleven selected fire types. Electrical cabinets were found to represent a majority (40.7%) of all the challenging fire events. Although historically conducted electrical cabinet fire experiments sought to explore the influence of parameters on HRR, the parameters were not systematically varied to statistically quantify which parameters were most important/relevant. Research in this study used statistical analysis on a series of simulation results on electrical cabinet fires from the computational fluid dynamics code Fire Dynamic Simulator (FDS). Simulation matrices were developed and evaluated using fractional factorial Design of Experiments (DOE) to screen the importance of different parameters on the electric cabinet HRR. Based on statistical analysis of the results, the combustible material surface area was found to be the most significant parameter followed by cabinet volume, combustible configuration, burning duration, and combustible material heat release rate per unit area. Material ignition temperature was found to not be statistically significant. The last phase of this research assessed the robustness of the electrical cabinet parameters on the predicted HRR with more detailed simulations. Two investigations were undertaken. To identify the nonlinear effects of parameters on the electrical cabinet fire HRR, a Response Surface Methodology (RSM) based Central Composite Design (CCD) was used to create a simulation matrix that would allow statistical analysis of important parameters as well as their effects on the fire heat release rate while keeping the combustible configuration inside the cabinet constant. A series of simulations were conducted to explore the impact of combustible configuration and ignition source location while keeping all other variables consistent. The analysis revealed that all variables had a statistically significant effect on peak HRR. For the average HRR, both the ventilation area into the cabinet and the ignition source HRR were found to be statistically insignificant. For both output variables, the cabinet volume, material heat release rate per unit area, and material surface area were the most significant parameters. Combustible configuration and ignition source location were also found to be statistically significant.
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    Design of a 10 kV SiC MOSFET-based high-density, high-efficiency, modular medium-voltage power converter
    Mocevic, Slavko; Yu, Jianghui; Fan, Boran; Sun, Keyao; Xu, Yue; Stewart, Joshua; Rong, Yu; Song, He; Mitrovic, Vladimir; Yan, Ning; Wang, Jun; Cvetkovic, Igor; Burgos, Rolando; Boroyevich, Dushan; DiMarino, Christina; Dong, Dong; Motwani, Jayesh Kumar; Zhang, Richard (IEEE, 2022-03)
    Simultaneously imposed challenges of high-voltage insulation, high dv/dt, high-switching frequency, fast protection, and thermal management associated with the adoption of 10 kV SiC MOSFET, often pose nearly insurmountable barriers to potential users, undoubtedly hindering their penetration in medium-voltage (MV) power conversion. Key novel technologies such as enhanced gatedriver, auxiliary power supply network, PCB planar dc-bus, and high-density inductor are presented, enabling the SiC-based designs in modular MV converters, overcoming aforementioned challenges. However, purely substituting SiC design instead of Sibased ones in modular MV converters, would expectedly yield only limited gains. Therefore, to further elevate SiC-based designs, novel high-bandwidth control strategies such as switching-cycle control (SCC) and integrated capacitor-blocked transistor (ICBT), as well as high-performance/high-bandwidth communication network are developed. All these technologies combined, overcome barriers posed by state-of-the-art Si designs and unlock system level benefits such as very high power density, high-efficiency, fast dynamic response, unrestricted line frequency operation, and improved power quality, all demonstrated throughout this paper.
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    Enhanced Gate-Driver Techniques and SiC-based Power-cell Design and Assessment for Medium-Voltage Applications
    Mocevic, Slavko (Virginia Tech, 2022-01-13)
    Due to the limitations of silicon (Si), there is a paradigm shift in research focusing on wide-bandgap-based (WBG) materials. SiC power semiconductors exhibit superiority in terms of switching speed, higher breakdown electric field, and high working temperature, slowly becoming a global solution in harsh medium-voltage (MV) high-power environments. However, to utilize the SiC MOSFET device to achieve those next-generation, high-density, high-efficiency power electronics converters, one must solve a plethora of challenges. For the MV SiC MOSFET device, a high-performance gate-driver (GD) is a key component required to maximize the beneficial SiC MOSFET characteristics. GD units must overcome associated challenges of electro-magnetic interference (EMI) with regards to common-mode (CM) currents and cross-talk, low driving loop inductance required for fast switching, and device short-circuit (SC) protection. Developed GDs (for 1.2 kV, and 10 kV devices) are able to sustain dv/dt higher than 100 V/ns, have less than 5 nH gate loop inductance, and SC protection, turning off the device within 1.5 us. Even with the introduction of SiC MOSFETs, power devices remain the most reliability-critical component in the converter, due to large junction temperature (Tj) fluctuations causing accelerated wear-out. Real-time (online) measurement of the Tj can help improve long-term reliability by enabling active thermal control, monitoring, and prognostics. An online Tj estimation is accomplished by generating integrated intelligence on the GD level. The developed Tj sensor exhibits a maximum error less than 5 degrees Celsius, having excellent repeatability of 1.2 degrees Celsius. Additionally, degradation monitoring and an aging compensation scheme are discussed, in order to maintain the accuracy of the sensor throughout the device's lifetime. Since ultra high-voltage SiC MOSFET devices (20 kV) are impractical, the modular multilevel converter (MMC) emerged as a prospective topology to achieve MV power conversion. If the kernal part of the power-cell (main constitutive part of the MMC converter) is an SiC MOSFET, the design is able to achieve very high-density and high-efficiency. To ensure a successful operation of the power-cell, a systematic design and assessment methodology (DAM) is explored, based on the 10 kV SiC MOSFET power-cell. It simultaneously addresses challenges of high-voltage insulation, high dv/dt and EMI, component and system protections, as well as thermal management. The developed power-cell achieved high-power density of 11.9 kW/l, with measured peak efficiency of n=99.3 %@10 kHz. It successfully operated at Vdc=6 kV, I=84 A, fsw>5 kHz, Tj<150 degrees Celsius and had high switching speeds over 100 V/ns. Lastly, to achieve high-power density and high-efficiency on the MV converter level, challenges of high-voltage insulation, high-bandwidth control, EMI, and thermal management must be solved. Novel switching cycle control (SCC) and integrated capacitor blocked-transistor (ICBT) control methodologies were developed, overcoming the drawbacks of conventional MMC control. These novel types of control enable extreme reduction in passive component size, increase the efficiency, and can operate in dc/dc, dc/ac, mode, potentially opening the modular converter to applications in which it was not previously used. In order to explore the aforementioned benefits, a modular, scalable, 2-cell per arm, prototype MV converter based on the developed power-cell is constructed. The converter successfully operated at Vdc=12 kV, I=28 A, fsw=10 kHz, with high switching speeds, exhibiting high transient immunity in both SCC and ICBT.
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    Epigenetic modulation of inflammation and synaptic plasticity promotes resilience against stress in mice
    Wang, Jun; Hodes, Georgia E.; Zhang, Hongxing; Zhang, Song; Zhao, Wei; Golden, Sam A.; Bi, Weina; Menard, Caroline; Kana, Veronika; Leboeuf, Marylene; Xie, Marc; Bregman, Dana; Pfau, Madeline L.; Flanigan, Meghan E.; Estebam-Fernández, Adelaida; Yemul, Shrishailam; Sharma, Ali; Ho, Lap; Dixon, Richard A.; Merad, Miriam; Han, Ming-Hu; Russo, Scott J.; Pasinetti, Giulio M. (Nature, 2018)
    Major depressive disorder is associated with abnormalities in the brain and the immune system. Chronic stress in animals showed that epigenetic and inflammatory mechanisms play important roles in mediating resilience and susceptibility to depression. Here, through a highthroughput screening, we identify two phytochemicals, dihydrocaffeic acid (DHCA) and malvidin-3′-O-glucoside (Mal-gluc) that are effective in promoting resilience against stress by modulating brain synaptic plasticity and peripheral inflammation. DHCA/Mal-gluc also significantly reduces depression-like phenotypes in a mouse model of increased systemic inflammation induced by transplantation of hematopoietic progenitor cells from stresssusceptible mice. DHCA reduces pro-inflammatory interleukin 6 (IL-6) generations by inhibiting DNA methylation at the CpG-rich IL-6 sequences introns 1 and 3, while Mal-gluc modulates synaptic plasticity by increasing histone acetylation of the regulatory sequences of the Rac1 gene. Peripheral inflammation and synaptic maladaptation are in line with newly hypothesized clinical intervention targets for depression that are not addressed by currently available antidepressants.
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    One thousand plant transcriptomes and the phylogenomics of green plants
    Leebens-Mack, James H.; Barker, Michael S.; Carpenter, Eric J.; Deyholos, Michael K.; Gitzendanner, Matthew A.; Graham, Sean W.; Grosse, Ivo; Li, Zheng; Melkonian, Michael; Mirarab, Siavash; Porsch, Martin; Quint, Marcel; Rensing, Stefan A.; Soltis, Douglas E.; Soltis, Pamela S.; Stevenson, Dennis W.; Ullrich, Kristian K.; Wickett, Norman J.; DeGironimo, Lisa; Edger, Patrick P.; Jordon-Thaden, Ingrid E.; Joya, Steve; Liu, Tao; Melkonian, Barbara; Miles, Nicholas W.; Pokorny, Lisa; Quigley, Charlotte; Thomas, Philip; Villarreal, Juan Carlos; Augustin, Megan M.; Barrett, Matthew D.; Baucom, Regina S.; Beerling, David J.; Benstein, Ruben Maximilian; Biffin, Ed; Brockington, Samuel F.; Burge, Dylan O.; Burris, Jason N.; Burris, Kellie P.; Burtet-Sarramegna, Valerie; Caicedo, Ana L.; Cannon, Steven B.; Cebi, Zehra; Chang, Ying; Chater, Caspar; Cheeseman, John M.; Chen, Tao; Clarke, Neil D.; Clayton, Harmony; Covshoff, Sarah; Crandall-Stotler, Barbara J.; Cross, Hugh; dePamphilis, Claude W.; Der, Joshua P.; Determann, Ron; Dickson, Rowan C.; Di Stilio, Veronica S.; Ellis, Shona; Fast, Eva; Feja, Nicole; Field, Katie J.; Filatov, Dmitry A.; Finnegan, Patrick M.; Floyd, Sandra K.; Fogliani, Bruno; Garcia, Nicolas; Gateble, Gildas; Godden, Grant T.; Goh, Falicia (Qi Yun); Greiner, Stephan; Harkess, Alex; Heaney, James Mike; Helliwell, Katherine E.; Heyduk, Karolina; Hibberd, Julian M.; Hodel, Richard G. J.; Hollingsworth, Peter M.; Johnson, Marc T. J.; Jost, Ricarda; Joyce, Blake; Kapralov, Maxim V.; Kazamia, Elena; Kellogg, Elizabeth A.; Koch, Marcus A.; Von Konrat, Matt; Konyves, Kalman; Kutchan, Toni M.; Lam, Vivienne; Larsson, Anders; Leitch, Andrew R.; Lentz, Roswitha; Li, Fay-Wei; Lowe, Andrew J.; Ludwig, Martha; Manos, Paul S.; Mavrodiev, Evgeny; McCormick, Melissa K.; McKain, Michael; McLellan, Tracy; McNeal, Joel R.; Miller, Richard E.; Nelson, Matthew N.; Peng, Yanhui; Ralph, Paula E.; Real, Daniel; Riggins, Chance W.; Ruhsam, Markus; Sage, Rowan F.; Sakai, Ann K.; Scascitella, Moira; Schilling, Edward E.; Schlosser, Eva-Marie; Sederoff, Heike; Servick, Stein; Sessa, Emily B.; Shaw, A. Jonathan; Shaw, Shane W.; Sigel, Erin M.; Skema, Cynthia; Smith, Alison G.; Smithson, Ann; Stewart, C. Neal, Jr.; Stinchcombe, John R.; Szovenyi, Peter; Tate, Jennifer A.; Tiebel, Helga; Trapnell, Dorset; Villegente, Matthieu; Wang, Chun-Neng; Weller, Stephen G.; Wenzel, Michael; Weststrand, Stina; Westwood, James H.; Whigham, Dennis F.; Wu, Shuangxiu; Wulff, Adrien S.; Yang, Yu; Zhu, Dan; Zhuang, Cuili; Zuidof, Jennifer; Chase, Mark W.; Pires, J. Chris; Rothfels, Carl J.; Yu, Jun; Chen, Cui; Chen, Li; Cheng, Shifeng; Li, Juanjuan; Li, Ran; Li, Xia; Lu, Haorong; Ou, Yanxiang; Sun, Xiao; Tan, Xuemei; Tang, Jingbo; Tian, Zhijian; Wang, Feng; Wang, Jun; Wei, Xiaofeng; Xu, Xun; Yan, Zhixiang; Yang, Fan; Zhong, Xiaoni; Zhou, Feiyu; Zhu, Ying; Zhang, Yong; Ayyampalayam, Saravanaraj; Barkman, Todd J.; Nam-Phuong Nguyen; Matasci, Naim; Nelson, David R.; Sayyari, Erfan; Wafula, Eric K.; Walls, Ramona L.; Warnow, Tandy; An, Hong; Arrigo, Nils; Baniaga, Anthony E.; Galuska, Sally; Jorgensen, Stacy A.; Kidder, Thomas I.; Kong, Hanghui; Lu-Irving, Patricia; Marx, Hannah E.; Qi, Xinshuai; Reardon, Chris R.; Sutherland, Brittany L.; Tiley, George P.; Welles, Shana R.; Yu, Rongpei; Zhan, Shing; Gramzow, Lydia; Theissen, Gunter; Wong, Gane Ka-Shu (2019-10-31)
    Green plants (Viridiplantae) include around 450,000-500,000 species(1,2) of great diversity and have important roles in terrestrial and aquatic ecosystems. Here, as part of the One Thousand Plant Transcriptomes Initiative, we sequenced the vegetative transcriptomes of 1,124 species that span the diversity of plants in a broad sense (Archaeplastida), including green plants (Viridiplantae), glaucophytes (Glaucophyta) and red algae (Rhodophyta). Our analysis provides a robust phylogenomic framework for examining the evolution of green plants. Most inferred species relationships are well supported across multiple species tree and supermatrix analyses, but discordance among plastid and nuclear gene trees at a few important nodes highlights the complexity of plant genome evolution, including polyploidy, periods of rapid speciation, and extinction. Incomplete sorting of ancestral variation, polyploidization and massive expansions of gene families punctuate the evolutionary history of green plants. Notably, we find that large expansions of gene families preceded the origins of green plants, land plants and vascular plants, whereas whole-genome duplications are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The increasing availability of high-quality plant genome sequences and advances in functional genomics are enabling research on genome evolution across the green tree of life.
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    PointMotionNet: Point-Wise Motion Learning for Large-Scale LiDAR Point Clouds Sequences
    Wang, Jun; Li, Xiaolong; Sullivan, Alan; Abbott, A. Lynn; Chen, Siheng (IEEE, 2022-06)
    We propose a point-based spatiotemporal pyramid architecture, called PointMotionNet, to learn motion information from a sequence of large-scale 3D LiDAR point clouds. A core component of PointMotionNet is a novel technique for point-based spatiotemporal convolution, which finds the point correspondences across time by leveraging a time-invariant spatial neighboring space and extracts spatiotemporal features. To validate PointMotionNet, we consider two motion-related tasks: point-based motion prediction and multisweep semantic segmentation. For each task, we design an end-to-end system where PointMotionNet is the core module that learns motion information. We conduct extensive experiments and show that i) for point-based motion prediction, PointMotionNet achieves less than 0.5m mean squared error on Argoverse dataset, which is a significant improvement over existing methods; and ii) for multisweep semantic segmentation, PointMotionNet with a pretrained segmentation backbone outperforms previous SOTA by over 3.3 % mIoU on SemanticKITTI dataset with 25 classes including 6 moving objects.
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    Power-cell switching-cycle capacitor voltage control for modular multi-level converters
    (United States Patent and Trademark Office, 2018-05-08)
    In a modular multi-level power converter, additional switching states are interleaved between main switching states that control output voltage or waveform. The additional switching states provide current from a DC-link to charge capacitors in respective modules or cells to an offset voltage from which the capacitor voltages are controlled toward a reference voltage during each switching cycle rather than being allowed to build up over a period of an output waveform of variable line frequency, possibly including zero frequency. Since the switching cycle is much shorter than the duration of a line frequency cycle and the capacitor voltages are balanced during each switching cycle, output voltage ripple can be limited as desired with a capacitor of much smaller value and size than would otherwise be required.
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    Self-calibrating optical fiber pressure, strain and temperature sensors
    (United States Patent and Trademark Office, 2000-05-30)
    Broadband energy incident on a transducer having partially or fully reflective surfaces separated by a gap which is greater than the coherence length of the broadband energy but smaller than one-half a coherence length of a band of energy within said broadband energy causes a portion of the spectral content of the broadband energy corresponding to a coherence length greater than twice the gap length to exhibit interference effects while the average power of the broadband energy remains unaffected. Splitting energy reflected from the transducer into two beams which are filtered at preferably similar center frequencies but with different pass bands yields beams which are radically different in sensitivity to changes in gap length. Analyzing the beams to derive a ratio of powers (since source intensity and fiber attenuation in a common fiber are thus self-cancelling) allows high accuracy and high resolution absolute measurement of temperature, pressure or strain. Effects of any of these physical parameters which are not of interest in a measurement can be fully compensated or made arbitrarily insignificant in a simple transducer structure of extremely small size. Use of broadband energy permits measurement over greater lengths of optical fiber.
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    A SiC-Based Liquid-Cooled Electric Vehicle Traction Inverter Operating at High Ambient Temperature
    Zhang, Chi; Srdic, Srdjan; Lukic, Srdjan; Wang, Jun; Burgos, Rolando (China Power Supply Society, 2022-06-30)
    This paper describes the design process of a high-power-density 100 kW (34 kW/L) traction inverter for electric vehicles, operating at an ambient temperature of 105 °C. A detailed thermal analysis is performed based on the thermal behavior of the switching devices, and the results are used to estimate the semiconductor device junction temperature and to determine the requirements of the cooling system to achieve the target power level. A high-temperature gate drive board aiming for reliable system operation in electric vehicles is developed. An overcurrent protection scheme based on parasitic inductance between the power source and the Kelvin source of the power module has been implemented. A dc-link decoupling snubber circuit is designed numerically based on a detailed forth-order high-frequency equivalent circuit of a double pulse test circuit. The approach to optimize the snubber circuit, not only for the voltage spike suppression but also for good thermal performance, is proposed. Finally, a hardware prototype with SiC power modules has been built and tested at 60 kW continuous power and 100 kW for 20 seconds at 105 °C ambient temperature and 65 °C inlet coolant temperature.
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    Switching-Cycle Control and Sensing Techniques for High-Density SiC-Based Modular Converters
    Wang, Jun (Virginia Tech, 2018-06-11)
    Nowadays high power density has become an emerging need for the medium-voltage (MV) high-power converters in applications of power distribution systems in urban areas and transportation carriers like ship, airplane, and so forth. The limited footprint or space resource cost such immensely high price that introducing expensive advanced equipment to save space becomes a cost-effective option. To this end, replacing conventional Si IGBT with the superior SiC MOSFET to elevate the power density of MV modular converters has been defined as the concentration of this research work. As the modular multilevel converter (MMC) is the most typical modular converter for high power applications, the research topic is narrowed down to study the SiC MOSFET-based MMC. Fundamentals of the MMC is firstly investigated by introducing a proposed state-space switching model, followed by unveiling all possible operation scenarios of the MMC. The lower-frequency energy fluctuation on passive components of the MMC is interpreted and prior-art approaches to overcome it are presented. By scrutinizing the converter's switching states, a new switching-cycle control (SCC) approach is proposed to balance the capacitor energy within one switching cycle is explored. An open-loop model-predictive method is leveraged to study the behavior of the SCC, and then a hybrid-current-mode (HCM) approach to realize the closed-loop SCC on hardware is proposed and verified in simulation. In order to achieve the hybrid-current-mode SCC (HCM-SCC), a high-performance Rogowski switch-current sensor (RSCS) is proposed and developed. As sensing the switching current is a critical necessity for HCM-SCC, the RSCS is designed to meet all the requirement for the control purposes. A PCB-embedded shielding design is proposed to improve the sensor accuracy under high dv/dt noises caused by the rapid switching transients of SiC MOSFET. The overall system and control validations have been conducted on a high-power MMC prototype. The basic unit of the MMC prototype is a SiC Power Electronics Building Block (PEBB) rated at 1 kV DC bus voltage. Owing to the proposed SCC, the PEBB development has achieved high power density with considerable reduction of passive component size. Finally, experimental results exhibit the excellent performance of the RSCS and the HCM-SCC.
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    Synchronized Communication Network for Real-Time Distributed Control Systems in Modular Power Converters
    Rong, Yu (Virginia Tech, 2022-11-08)
    Emerging large-scale modular power converters are pursuing high-performance distributed control systems. As opposed to the centralized control architecture, the distributed control architecture features shared computational burdens, pulse-width modulation (PWM) latency compensation, simplified fiber-optic cable connection, redundant data routes, and greatly enhanced local control capabilities. Modular multilevel converters (MMCs) with conventional control are subjected to large capacitor voltage ripples, especially at low-line frequencies. It is proved that with appropriate arm current shaping in the timescale of a switching period, referred as the switching-cycle control (SCC), such line-frequency dependence can be eliminated and MMCs are enabled to work even in dc-dc mode. Yet the SCC demands multiple times of arm current alternations in one switching period. To achieve the high-bandwidth current regulation, hybrid modulation approach incorporating both the carrier-based modulation and the peak-current-mode (PCM) modulation is adopted. The combined digital and analog control and the extreme time-sensitive nature together pose great challenges on the practical implementation that the existing distributed control systems cannot cope with. This dissertation aims to develop an optimized distributed control system for SCC implementation. The critical analog PCM modulation is enabled by the intelligent gate driver with integrated rogowski coil and field programmable gate array (FPGA). A novel distributed control architecture is proposed accordingly for SCC applications where the hybrid modulation function is shifted to the gate driver. The proposed distributed control solution is verified in the SCC-based converter operations. Accompanied by the growing availability of medium-voltage silicon carbide (SiC) devices, fast-switching-enabled novel control schemes raise a high synchronization requirement for the communication network. Power electronics system network (PESNet) 3.0 is a proposed next-generation communication network designed and optimized for a distributed control system. This dissertation presents the development of PESNet 3.0 with a sub-nanosecond synchronization error (SE) and a gigabits-per-second data rate dedicated for large-scale high-frequency modular power converters. The White Rabbit Network technology, originally developed for the Large Hadron Collider accelerator chain at the European Organization for Nuclear Research (CERN), has been embedded in PESNet 3.0 and tailored to be suited for distributed power conversion systems. A simplified inter-node phase-locked loop (N2N-PLL) has been developed. Subsequently, stability analysis of the N2N-PLL is carried out with closed-loop transfer function measurement using a digital perturbation injection method. The experimental validation of the PESNet 3.0 is demonstrated at the controller level and converter level, respectively. The latter is on a 10 kV SiC-MOSFET-based modular converter prototype, verifying ±0.5 ns SE at 5 Gbps data rate for a new control scheme. The communication network has an impact on the converter control and operation. The synchronicity of the controllers has an influence on the converter harmonics and safe operation. A large synchronization error can lead to the malfunction of the converter operation. The communication latency poses a challenge to the converter control frequency and bandwidth. With the increased scale of the modular converter and control frequency, the low-latency requirement of communication network becomes more stringent.
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    A Synchronous Distributed Control and Communication Network for High-Frequency SiC-Based Modular Power Converters
    Rong, Yu (Virginia Tech, 2019-12-06)
    Numerous power electronics building blocks (PEBB) based power conversion systems have been developed to explore modular design, scalable voltage and current ratings, low-cost operations, etc. This paper further extends the modular concept from the power stage to the control system. The communication network in SiC-based modular power converters is becoming significant for distributed control architecture, with the requirements of tight synchronization and low latency. The influence of the synchronization accuracy on harmonics under the phase-shifted carrier pulse width modulation (PSC-PWM) is evaluated. When the synchronization is accurate, the influence of an increase in harmonics can be ignored. Thus, a synchronous distributed control and communication protocol with well-performed synchronization of 25 ns accuracy is proposed and verified for a 120 kHz SiC-based impedance measurement unit (IMU) with cascaded H-bridge PEBBs. An improved synchronization method with additional analog circuits is further implemented and verified with sub-ns synchronization accuracy.
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    Vidi: a Lightweight Protocol Between Visualization Systems and Digital Libraries
    Wang, Jun (Virginia Tech, 2002-04-26)
    Achieving interoperability between digital libraries and visualization tools is a difficult problem. To solve this problem, a version of the Open Archives Initiative (OAI) Protocol for Metadata Harvesting called VIDI is proposed. It is a lightweight protocol, which contains only 5 request verbs -- Identify, ListMetadataFormats, ListVisdataFormats, ListTransformers, and RequestResultSet. It is extended from the OAI protocol, which enables its simplicity and wider acceptability. It is flexible, which avoids a rigid architecture in implementation. It is general, so it can apply to all kinds of Visualization Systems and Digital Libraries. But most importantly, it reaches our goal of enabling operability between Visualization Systems and Digital Libraries. The protocol design and implementation details are given. Two prototype systems are implemented to demonstrate the above features. Implementation details are given about ENVISION-ODL and ENVISION-MARIAN. Analysis, evaluation, and conclusions reinforce the discussion of the benefits of VIDI.