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1. A Complete Design of a High Frequency Medium Voltage Multi-Port Transformer

   https://doi.org/10.1109/ICRERA47325.2019.8997088  

   El Shafei, Ahmad; Ozdemir, Saban; Altin, Necmi; Jean-Pierre, Garry; Nasiri, Adel (November 2019, 2019 8th International Conference on Renewable Energy Research and Applications (ICRERA))

   null (Ed.)

   In this paper, design of a compact high frequency four-port transformer for a Solid-State Transformer (SST) arrangement is presented. Unlike other SSTs, the four-port system integrates three active sources and a load port with galvanic isolation via a single transformer core. In addition to this feature, one of the three source ports is designed to operate at Medium Voltage (MV) 7.2kV for direct connection to 4.16kV AC grid, while other ports nominal voltages are rated at 400V. The transformer is designed to operate at 50kHz and to supply 25kW/port. Thus, the proposed system connects the MV grid, Energy Storage System (ESS), PV, and DC load to each other on a single common transformer core. Based on the system power demand and availability of renewable energy resources, utility and energy storage ports can either supply or draw power, while PV port can only supply power, maintaining the required demand for the load. This work focuses mainly on the High Frequency Transformer (HFT) design. An extensive study is carried out to obtain the optimal, compact, cost effective, and high efficiency model. Modeling, mathematical, and simulation results are derived and presented to demonstrate the viability of this design. 

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2. A SiC-based power electronics interface for integrating a battery energy storage into the medium (13.8 kV) distribution system

   https://doi.org/10.1109/APEC.2018.8341350  

   Umuhoza, Janviere; Mhiesan, Haider; Mordi, Kenneth; Farnell, Chris; Mantooth, H. Alan (March 2018, APEC 2018)

   This paper describes the study of a topology of modular multilevel converters for integrating battery energy storage into a medium (13.8 kV) distribution system. The main benefit of this topology is to remove the need for a bulk 60 Hz transformer that is normally used to step up the output of a voltage source inverter to the medium voltage level. A SiC-based power electronics interface presented in this paper provides an efficient solution without the large and costly transformer. Using medium voltage SiC devices (≥ 10 kV SiC MOSFETs), with their high breakdown voltage, enables the system to meet and withstand medium voltage application, using a minimized number of cascaded modules. This SiC-based power electronics interface significantly reduces the complexity usually faced when Si devices are used directly in medium voltage applications. The voltage and state of charge balancing control for battery modules is also simplified and performs well. The simulation and experimental results, performed on a low-voltage prototype, verify the proposed topology that is presented in this paper. 

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3. Design and Implementation of a Medium Voltage, High Power, High Frequency Four-Port Transformer

   https://doi.org/10.1109/APEC39645.2020.9124337  

   El Shafei, Ahmad; Ozdemir, Saban; Altin, Necmi; Jean-Pierre, Garry; Nasiri, Adel (March 2020, 2020 IEEE Applied Power Electronics Conference and Exposition (APEC))

   null (Ed.)

   With the growth in penetration number and power level of renewable energy resources, the need for a compact and high efficient solid state transformer becomes more important. The aim of this paper is to design a compact solid state transformer for microgrid application. The proposed transformer has four ports integrated on a single common core. Thus, it can integrate different renewable energy resources and energy storage systems. The transformer is operating at 50kHz switching frequency, and each port can handle 25kW rated power. In this paper, the ports are chosen to represent a realistic industrial microgrid model consisting of grid, energy storage system, photovoltaic system, and load. The grid port is designed to operate at 4160V AC, while the other three ports operate at 400V. Moreover, the grid, energy storage, and photovoltaic ports are active ports with dual active bridge topologies, while the load port is a passive port with full bridge rectifier one. In this paper, an extensive and complete design and modeling of the entire solid state transformer is presented. The proposed design is first validated with simulation results, and then the proposed transformer is implemented. Some preliminary experimental tests are also performed and the obtained results are reported. 

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4. Virtual Prototyping Process For Assessment of Medium Voltage Grid-Connected Solid State Transformer Implementations

   https://doi.org/10.1109/ECCE47101.2021.9595786  

   Siddaiah, Rounak; Vygoder, Mark; Cuzner, Robert M; Ordonez, Juan C.; Chagas, Mauricio B. (October 2021, 2021 IEEE Energy Conversion Congress and Exposition (ECCE))

   This paper presents a unique Virtual Prototyping Process (VPP) that allows for metaheuristic optimization of the building block based Power Electronic Converter systems. The VPP allows for exploration of a range of design space variables, including voltage levels, power semiconductor device technology and thermal management approach against competing objectives such as power density, efficiency and specific cost given electrical and environmental constraints. A unique feature of proposed VPP is compilation of lower voltage building blocks into a much higher voltage rated system and inclusion of allocations for insulation systems, thermal management, accessibility, busing/interconnections and frame/structure/chassis. This approach enables understanding of these practical considerations on power density. This paper presents a use case of a Medium Voltage ac (MVac) to Low Voltage dc (LVdc) solid state transformer. 

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5. TransEHR: Self-Supervised Transformer for Clinical Time Series Data

   Xu, Yanbo; Xu, Shangqing; Ramprassad, Manav; Tumanov, Alexey; Zhang, Chao (December 2023, Proceedings of Machine Learning Research)

   Deep neural networks, including the Transformer architecture, have achieved remarkable performance in various time series tasks. However, their effectiveness in handling clinical time series data is hindered by specific challenges: 1) Sparse event sequences collected asynchronously with multivariate time series, and 2) Limited availability of labeled data. To address these challenges, we propose Our code is available at https://github.com/SigmaTsing/TransEHR.git . , a self-supervised Transformer model designed to encode multi-sourced asynchronous sequential data, such as structured Electronic Health Records (EHRs), efficiently. We introduce three pretext tasks for pre-training the Transformer model, utilizing large amounts of unlabeled structured EHR data, followed by fine-tuning on downstream prediction tasks using the limited labeled data. Through extensive experiments on three real-world health datasets, we demonstrate that our model achieves state-of-the-art performance on benchmark clinical tasks, including in-hospital mortality classification, phenotyping, and length-of-stay prediction. Our findings highlight the efficacy of in effectively addressing the challenges associated with clinical time series data, thus contributing to advancements in healthcare analytics. 

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