@article{baek_bhattacharya_2019, title={Isolation Transformer for 3-Port 3-Phase Dual-Active Bridge Converters in Medium Voltage Level}, volume={7}, ISSN={["2169-3536"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85062211518&partnerID=MN8TOARS}, DOI={10.1109/ACCESS.2019.2895818}, abstractNote={In this paper, an isolation transformer with integrated filter inductances for three-phase three-port dual-active bridge (DAB) converters in the wye-wye-delta (Yyd) configuration is introduced and designed. A large number of ports and phases in the application necessarily requires a proportionally increased number of components, accessories, and connections. These additional parts induce significant losses and electromagnetic interference during high-frequency operations. Hence, fully manipulating the parasitic components, especially the leakage inductances of the transformer as the circuit element in the interconnected multi-port configuration, is a key to reduce the system’s overall size and to improve its reliability. The proposed geometry and design method enables the full integration of a large number of otherwise bulky inductors to be included in the isolation transformers so that the latter function not only a step-up/down transformers but also as filter networks required for three-port DAB operations. The transformer is suitable for high-power and high step-up/down ratio dc-dc converters, which prefers a parallel combination of converters that share current, on the low-voltage side. The operating principles and steady-state analysis are presented with respect to power flow, and a three-winding shell-type isolation/filter transformer has been designed for a three-port three-phase Yyd DAB converter for solid state transformer applications. The finite element method simulations are used to validate the feasibility of the proposed approach. A prototype was fabricated and tested in an experimental setting.}, journal={IEEE ACCESS}, author={Baek, Seunghun and Bhattacharya, Subhashish}, year={2019}, pages={19678–19687} }
 @article{baek_bhattacharya_2018, title={Analytical Modeling and Implementation of a Coaxially Wound Transformer With Integrated Filter Inductance for Isolated Soft-Switching DC-DC Converters}, volume={65}, ISSN={["1557-9948"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85028532226&partnerID=MN8TOARS}, DOI={10.1109/tie.2017.2740855}, abstractNote={In this paper, we propose an approach for integrating a series filter inductance in a coaxially wound transformer (CWT) as a potential alternative to conventional solenoidally wound transformers (SWT) for high-power isolated soft-switching dc–dc converters. The critical elements that determine the size and the performance of soft-switching dc–dc converters are the isolation transformer and the filter elements. While conventional SWTs using a stray magnetic field as a filter inductance often suffer from a considerably increased loss, heat congestion, and electromagnetic interference, a CWT is rarely affected by high frequency and fringing effects. The desired properties are still valid while the required filter inductance is fully integrated with an isolation transformer using the proposed method. In addition, the evenly distributed magnetic fields in a concentric geometry enable accurate electrical and mechanical analysis and a specific application-oriented design. In this paper, the operating principles, design procedure, and loss modeling of a CWT with an integrated filter inductance are introduced. Its functionality and suitability for high-frequency applications were proven by theoretical analysis and experiments. A prototype transformer with an integrated inductance 4 mH was facilitated and evaluated in a 15 kV-SiC  mosfet-based 6 k–400 Vdc stage for a solid-state transformer of up to 6.5 kW at a switching frequency of 20 kHz.}, number={3}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, author={Baek, Seunghun and Bhattacharya, Subhashishi}, year={2018}, month={Mar}, pages={2245–2255} }
 @inproceedings{baek_roy_bhattacharya_kim_2013, title={Power flow analysis for 3-port 3-phase dual active bridge dc/dc converter and design validation using high frequency planar transformer}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84891090658&partnerID=MN8TOARS}, DOI={10.1109/ecce.2013.6646727}, abstractNote={In this paper, an inductor-integrated three-winding shell-type planar transformer is designed and analyzed for three-port dual-active bridge (DAB) dc/dc converters in wye wye-delta connection. The steady-state operation principle of the proposed topology has been studied and design parameters of the isolation transformer are analytically determined. The proposed geometry and design method for the ac-link transformer allows us to integrate a large number of bulky inductors required for three phase DAB operation to the transformer without additional connections and unanticipated parasitic effects. It also considerably simplifies the equivalent leakage inductance circuit model and power flow analysis. This configuration is suitable for high power and high step up/down ratio dc/dc converter applications which requires series and/or parallel combination of converters. The experimental and FEM simulation results from prototypes are presented and it validates the theoretical considerations and feasibility of the proposed approach for isolated dc/dc converter applications such as solid-state transformer (SST).}, booktitle={2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013}, author={Baek, S. and Roy, S. and Bhattacharya, Subhashish and Kim, S.}, year={2013}, pages={388–395} }
 @inproceedings{baek_bhattacharya_cougo_ortiz_2012, title={Accurate equivalent circuit modeling of a medium-voltage and high-frequency coaxial winding DC-link transformer for solid state transformer applications}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84870918183&partnerID=MN8TOARS}, DOI={10.1109/ecce.2012.6342645}, abstractNote={The 12kV-400V dc-dc stage of a distribution level solid state transformers (SST) has been under research and development. Development of a 15kV SiC Mosfet allows a single stage of the dc-dc converter to operate at medium voltage at an operating frequency of over 20kHz. Nonetheless, the high rising and falling time during pulse switching in the dual active bridge operation is another significant obstacle to realize this technology. In order to understand and predict the frequency response with pulse switching and consider common-mode response via circuit analysis accurately, lumped-element equivalent circuit model has been developed for broadband coaxial winding transformer (CWT) with analytic expressions. The simple lumped-element equivalent circuit introduced in this paper has been verified by measurement results from a prototype for a medium-voltage (MV) and high frequency (HF) coaxial winding power transformer up to the frequency where the length of the coaxial body is a quarter of a wavelength and further study up to 30MHz has been described.}, booktitle={2012 IEEE Energy Conversion Congress and Exposition, ECCE 2012}, author={Baek, S.S. and Bhattacharya, Subhashish and Cougo, B. and Ortiz, G.}, year={2012}, pages={1439–1446} }
 @inproceedings{baek_bhattacharya_2011, title={Analytical modeling of a medium-voltage and high-frequency resonant coaxial-type power transformer for a solid state transformer application}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-81855185904&partnerID=MN8TOARS}, DOI={10.1109/ecce.2011.6064014}, abstractNote={This paper introduces a unique medium-voltage and high-frequency resonant coaxial-type power transformer (RCT) for a power-distribution level Solid State Transformer (SST) application [1]. The dc-dc stage of the SST application requires a compact high performance resonant transformer that operates under high electric stress and frequency. The RCT discussed in this work brings the virtues of the coaxial-type transformer, which has been use in radio frequency applications, to medium-voltage power conversion applications. The high frequency parasitic effects, which are negligible at 60Hz, become a significant concern in a SST operating above kHz range. Hence, the parasitics of the transformer need to be accurately predicted and controlled for quality power control and safety. The RCT not only minimizes the parasitics of the transformer but also integrates a resonant tank comprised of a series inductance and shunt capacitance by utilizing the stray magnetic and electric flux within the transformer. The limited space in compact size is efficiently used and materials can be optimized. The unique analytic design method of an RCT is introduced and the equivalent circuit model is developed in this paper. The specific design is based on the high performance transformer for a dual-active bridge (DAB) converter, which is one of the most popular topologies in bidirectional power conversion, in the dc-dc stage of the SST application being developed at the FREEDM System Center and its concept is verified with FEM analysis and experiments.}, booktitle={IEEE Energy Conversion Congress and Exposition: Energy Conversion Innovation for a Clean Energy Future, ECCE 2011, Proceedings}, author={Baek, S. and Bhattacharya, Subhashish}, year={2011}, pages={1873–1880} }
 @inproceedings{wang_baek_elliott_kadavelugu_wang_she_dutta_liu_zhao_yao_et al._2011, title={Design and hardware implementation of Gen-1 silicon based solid state transformer}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79955785263&partnerID=MN8TOARS}, DOI={10.1109/apec.2011.5744766}, abstractNote={This paper presents the design and hardware implementation and testing of 20kVA Gen-1 silicon based solid state transformer (SST), the high input voltage and high voltage isolation requirement are two major concerns for the SST design. So a 6.5kV 25A dual IGBT module has been customized packaged specially for this high voltage low current application, and an optically coupled high voltage sensor and IGBT gate driver has been designed in order to fulfill the high voltage isolation requirement. This paper also discusses the auxiliary power supply structure and thermal management for the SST power stage.}, booktitle={Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC}, author={Wang, G. and Baek, S. and Elliott, J. and Kadavelugu, A. and Wang, F. and She, X. and Dutta, S. and Liu, Y. and Zhao, T. and Yao, W. and et al.}, year={2011}, pages={1344–1349} }
 @inproceedings{kadavelugu_baek_dutta_bhattacharya_das_agarwal_scofield_2011, title={High-frequency design considerations of dual active bridge 1200 V SiC MOSFET DC-DC converter}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79955786991&partnerID=MN8TOARS}, DOI={10.1109/apec.2011.5744614}, abstractNote={Silicon carbide (SiC) is more favorable than Silicon (Si) to build high voltage devices due its wider band-gap and higher critical field strength. Especially, the SiC MOSFETs are finding their niche in 1 kV range, which is currently dominated by Si IGBTs. This paper aims at demonstrating high power and high frequency operation of the SiC MOSFETs, as a means to evaluate the feasibility of using SiC MOSFETs for high power density applications. The sample devices chosen for this study are 1200 V, 20 A, SiC MOSFETs co-packed with 10 A JBS diodes — manufactured by the CREE Inc. A dual active bridge (DAB) converter has been built to validate the suitability of SiC devices for high power density converters. The design details of the DAB hardware, and the high frequency transformer used for interfacing both the bridges are given. Experimental results on the DAB at 100 kHz switching frequency are presented. Finally, the device switching waveforms up to 1 MHz are given.}, booktitle={Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC}, author={Kadavelugu, A. and Baek, S. and Dutta, S. and Bhattacharya, Subhashish and Das, M. and Agarwal, A. and Scofield, J.}, year={2011}, pages={314–320} }
 @inproceedings{hatua_dutta_tripathi_baek_karimi_bhattacharya_2011, title={Transformer less intelligent power substation design with 15kV SiC IGBT for grid interconnection}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-81855226026&partnerID=MN8TOARS}, DOI={10.1109/ecce.2011.6064346}, abstractNote={Basic power topology for a Solid State Transformer (SST) with new 15kV SiC IGBT devices is discussed. It is difficult to build high efficient, light weight, magnetically isolated solid state transformer for high voltage (13.8 kV) grid connectivity with existing Si 6.5kV rated IGBTs and diodes. Existing state of the art high voltage (6.5kV), high speed power devices (IGBT) cause considerable amount of loss (switching and conduction loss). With the advent of SiC devices these limitations are largely mitigated and this provides the motivation for new power topologies. The targeted efficiency of the proposed SST is 98%.Simulation results for a 1 MVA proposed SST topology is presented.}, booktitle={IEEE Energy Conversion Congress and Exposition: Energy Conversion Innovation for a Clean Energy Future, ECCE 2011, Proceedings}, author={Hatua, K. and Dutta, S. and Tripathi, A. and Baek, S. and Karimi, G. and Bhattacharya, Subhashish}, year={2011}, pages={4225–4232} }
 @article{bhattacharya_zhao_wang_dutta_baek_du_parkhideh_zhou_huang_2010, title={Design and Development of Generation-I Silicon based Solid State Transformer}, ISSN={["1048-2334"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77952195486&partnerID=MN8TOARS}, DOI={10.1109/apec.2010.5433455}, abstractNote={The Solid State Transformer (SST) is one of the key elements proposed in the National Science Foundation (NSF) Generation-III Engineering Research Center (ERC) “Future Renewable Electric Energy Delivery and Management” (FREEDM) Systems Center. The SST is used to enable active management of distributed renewable energy resources, energy storage devices and loads. In this paper, the Generation-I SST single-phase 20kVA, based on 6.5kV Si-IGBT is proposed for interface with 12kV distribution system voltage. The SST system design parameters, overall system efficiency, high frequency transformer design, dual active bridge converter, auxiliary power supply and gate drives are investigated. Design considerations and experimental results of the prototype SST are reported.}, journal={2010 TWENTY-FIFTH ANNUAL IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION (APEC)}, author={Bhattacharya, Subhashish and Zhao, Tiefu and Wang, Gangyao and Dutta, Sumit and Baek, Seunghun and Du, Yu and Parkhideh, Babak and Zhou, Xiaohu and Huang, Alex Q.}, year={2010}, pages={1666–1673} }
 @inproceedings{baek_du_wang_bhattacharya_2010, title={Design considerations of high voltage and high frequency transformer for solid state transformer application}, booktitle={Iecon 2010: 36th annual conference of the ieee industrial electronics society}, author={Baek, S. and Du, Y. and Wang, G. Y. and Bhattacharya, S.}, year={2010} }
 @inproceedings{du_baek_bhattacharya_huang_2010, title={High-voltage high-frequency transformer design for a 7.2kV to 120V/240V 20kVA solid state transformer}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78751558902&partnerID=MN8TOARS}, DOI={10.1109/iecon.2010.5674828}, abstractNote={Solid state transformer (SST) exhibits good features such as high power density, small volume and weight, controlled power factor, voltage sag ride through, etc. compared with traditional line frequency transformer. The 7.2kV AC to 120V/240V AC 20kVA solid state transformer is a key component of the future renewable electric energy delivery and management (FREEDM) systems as the interface between the 7.2kV distribution grid and the low voltage residential micro-grid. Three cascaded 6.7kVA high-voltage high-frequency transformers operating at 3kHz are employed to convert voltage from 3800V high voltage DC link of each cascaded stage to 400V low voltage DC link. The transformer is required to withstand at least 15kV high frequency voltage insulation continuously. Transformer magnetic core materials were reviewed and compared. Winding layout alternatives for leakage, magnetizing inductance and insulation were compared. An insulation strategy based on split core and separate winding structure with inserted insulation layer between the C cores was proposed. One 6.7kVA high voltage high frequency transformer prototype was built and the test results were reported.}, booktitle={IECON Proceedings (Industrial Electronics Conference)}, author={Du, Y. and Baek, S. and Bhattacharya, Subhashish and Huang, A.Q.}, year={2010}, pages={493–498} }