Tutorial Title: Design and Optimization of High-Power High-frequency Transformers for Solid-State Transformers

Solid-state transformers (SST) are widely applied in the AC/DC hybrid distribution networks to implement energy routing and to increase efficiency and power density. Isolated DC-DC converters are the key stages of the SSTs, which require high-power high-frequency transformers to provide the proper voltage transfer ratio and to help realize soft switching. The design and optimization of high-power high-frequency transformers are presented in this lecture. Two major solutions of high-power high-frequency transformers, namely litz-wire transformers and planar transformers, are investigated and compared, including the design and applications. The loss modeling methods are proposed, including that of winding losses for both litz wires and PCB windings, and that of core losses, in particular the eddy losses. The insulation design and the magnetic integration design are also analyzed for litz-wire transformers and planar transformers respectively. In addition, the optimization methods of high-power high-frequency transformers are introduced, along with novel methods based on intelligent algorithms.

Presenters’  Information

Kai Sun, Tsinghua University

Kai Sun received the B.E., M.E., and Ph.D. degrees in electrical engineering from Tsinghua University, in 2000, 2002, and 2006, respectively. He joined the faculty of Electrical Engineering, Tsinghua University, in 2006, where he is currently a Tenured Associate Professor (Research Professor). From Sep 2009 to Aug 2010, he was a Visiting Scholar at Department of Energy Technology, Aalborg University, Aalborg, Denmark. From Jan to Aug 2017, he was a Visiting Professor at Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Canada. His research interests include power electronics for renewable generation systems, microgrids, and energy internet.

Dr. Sun serves as an Associate Editor for IEEE Transactions on Power Electronics, IEEE Journal of Emerging and Selected Topics in Power Electronics, and Journal of Power Electronics. Dr. Sun served as the TPC Vice Chair of IEEE ECCE2017 and IEEE ECCE-Asia2017, the Organization Committee Chair of IEEE eGrid2019, and the Publicity Chair of IEEE ECCE2020. He also served as the General Co-Chair of 2018 International Future Energy Challenge (IFEC2018). Dr. Sun serves as PELS Asia Pacific Regional Vice Chair, PELS Beijing Chapter Chair and PELS Electronic Power Grid Systems Technical Committee (TC8) Secretary. He was a recipient of Delta Young Scholar Award in 2013, and Youth Award of China Power Supply Society (CPSS) in 2017, and IEEE Transactions on Power Electronics' Outstanding Reviewers Award in 2019.

Presenters’  Information

Zheyuan Yi, Tsinghua University

Zheyuan Yi received the B.S. degree in electrical engineering from Tsinghua University, Beijing, China in 2019. She is currently working toward the Ph.D. degree at Department of Electrical Engineering, Tsinghua University.

Her research interests include design and optimization of high-power high-frequency transformer and design of isolated bidirectional DC-DC converter.

Tutorial Title: Modeling and Reduction of Common-Mode Noise in Power Converters

This talk provides the modeling and reduction of common-mode (CM) noise in power converters. In the first part, the CM noise modeling approaches are presented. The transformer inter-winding capacitance, a critical propagation path for the CM noise in isolated power converters, will be investigated. After that, a generalized lumped capacitance model will be discussed, which describes the behavior of CM noise propagation for high frequency transformer. Based on the lumped capacitance model, the equivalent noise source (ENS) concept will be introduced for deriving the CM noise model of basic isolated power converters, and the effect of circuit configuration on the CM noise will be further discussed. In the second part, the CM noise reduction techniques will be expolred. The shielding-cancellation (SC) technique and the hybrid passive cancellation (HPC) method are firstly investigated, which improves the CM noise reduction of conventional shielding technique. For the converter with a complicated CM noise propagation path, such as the phase-shift full-bridge (PSFB) converter, the CM noise reduction by combining symmetry circuit and passive cancellation will be presented. Finally, the CM voltage cancellation (CMVC) method will be provided for a better understanding of the CM noise reduction techniques in power converters.

Presenters’  Information

Lihong Xie, Nanjing University of Aeronautics and Astronautics

Dr. Lihong Xie is currently a Research Fellow at the College of Automation Engineering of Nanjing University of Aeronautics and Astronautics (NUAA).

He received the B. S. and Ph. D. degrees in electrical engineering from Nanjing University of Aeronautics and Astronautics (NUAA), Nanjing, China, in 2012 and 2018, respectively. From November 2018 to August 2022, he worked as a research associate in the Electrical Energy Management Group (EEMG) at the University of Bristol as part of its work with the EPSRC Centre for Power Electronics. Since October 2022, he joined the College of Automation in NUAA. His current research interests include transformer modeling, conducted EMI and virtual prototyping of power converters.

Tutorial Title: Topologies and Control of Multilevel Converters

The controllability of capacitor voltages in multilevel converters is essential to enable their use in practice. This includes the voltage balancing of the dc-link capacitors and the flying capacitor (FC) voltage control. When the number of voltage levels of neutral-point-clamped (NPC) converters is four or higher, the capacitor voltage control becomes particularly challenging. To address this issue, various new hybrid multilevel topologies and new modulation and control strategies have been proposed with many recent developments. In particular, the virtual vector/zero modulation, combined with optimal zero-sequence injection, has shown superior capability to balance the dc-link capacitor voltages through software, without the need of additional hardware. This enables conventional NPC converters with four or higher number of levels to operate independently as a single rectifier or inverter (or with a passive front end) over the full power factor and modulation index range. This tutorial will answer questions such as: How can we derive the various multilevel topologies integrating semiconductor devices, dc-link capacitors, and flying capacitors? How do we enable their capacitor voltage balance through modulation and control? This tutorial will cover the basic multilevel converter topologies, their control, and their applications. It is suitable for researchers interested in multilevel converters at various levels.

Presenters’  Information

Xibo Yuan, China University of Mining and Technology

Professor Xibo Yuan received the B.S. degree from the China University of Mining and Technology, Xuzhou, China, and the Ph.D. degree from Tsinghua University, Beijing, China, in 2005 and 2010, respectively, both in electrical engineering. He has held Professor positions at the China University of Mining and Technology and the University of Bristol. He is a Distinguished Lecturer of the IEEE Power Electronics Society, a Fellow of IET and received several best paper awards from IEEE journals and conferences and the Isao Takahashi Power Electronics Award in 2018.

His research interests include power electronics and motor drives, wind power generation, multilevel converters, application of wide-bandgap devices, electric vehicles and more electric aircraft technologies.

Tutorial Title: Recent Advances on Modular Multilevel Converters

Modular multilevel converters have achieved significant success in the area of high-power applications (high-voltage direct-current, renewable energy conversion, motor drives, power distribution systems, transportation). The purpose of this tutorial is to provide a systematic overview of the multilevel converters in terms of their operation principles, latest achievements, emerging applications, and remaining challenges. The tutorial will start introducing the structure and basic operation principles of the modular multilevel converters. And then, the tutorial will introduce the fault detection of submodules and fault tolerant control scheme. Afterwards, the tutorial will introduce the control of the modular multilevel converter under ac-grid faults, as well as the protection of the modular multilevel converter under dc line short-circuit faults.

Presenters’  Information

Fujin Deng, Southeast University

Fujin Deng received the Ph.D. degree in Energy Technology from the Department of Energy Technology, Aalborg University, Aalborg, Denmark, in 2012. He joined the Southeast University in 2017 and is currently a Professor in the School of Electrical Engineering and the Head of Department of Power Electronics, Southeast University, Nanjing, China. From 2013 to 2015 and from 2015 to 2017, he was a Postdoctoral Researcher and an Assistant Professor, respectively, in the Department of Energy Technology, Aalborg University, Aalborg, Denmark. He has conducted a number of research projects and published more than 100 journal papers and a book on Modualr Multilevel Converter in WILEY-IEEE PRESS. His main research interests include multilevel converters, high-voltage direct-current transmission technology, wind power generation, and offshore wind farm-power systems dynamics.

Presenters’  Information

Qiang Yu, Southeast University

Qiang Yu received the B. Eng. degree in Electrical Engineering from Jilin University, Changchun, China, in 2017. He is currently working toward the Ph. D. degree with the School of Electrical Engineering, Southeast University, Nanjing, China. He was a visiting Ph. D student in the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, from 2021 to 2022. Mr. Yu has published 8 peer-reviewed journal articles and held 4 issued patents. His main research fields include the control and fault diagnosis of modular multilevel converter (MMC).

Tutorial Title: Power Converters for Resilient Bipolar DC Distribution Grids

The transition from a predominantly fossil fuel-based power generation towards renewable power sources, predominantly wind turbines and photovoltaic systems, inevitably leads towards an energy supply system that greatly depends on power electronics to feed the energy in the electrical grid. As all power electronic driven systems are intrinsically DC sources or loads, DC transmission and distribution systems become evident, not only because it is more efficient and cost effective, but also increases the ampacity of cables.

Similar to AC distribution grids, which are configured in single- or three-phase systems, the DC distribution grids can be configured in monopole or bipolar structures. Compared to monopole systems, bipolar DC distribution grids are with numerous benefits, e.g., multiple available voltage levels and resilience of power delivery in case of a wire failure. This tutorial will present recent advancements in power conversion technologies for bipolar LVDC and MVDC distribution systems. Several novel converter topologies of AC-DC and DC-DC converters for LVDC and MVDC applications will be addressed, which are inherently capable of bipolar operation. These topologies are based on the concept of topological integration of voltage balancers, which are required individually in classic approaches for maintaining voltage balance of bipolar DC grids. With such integration technique, bipolar operation capability of dc-link can be obtained with minimum costs and conversion losses.

Presenters’  Information

Shenghui Cui, Seoul National University

Shenghui Cui (Member, IEEE) received the B.S. degree from Tsinghua University, Beijing, China, in 2012, the M.S. degree from Seoul National University, Seoul, South Korea, in 2014, and the Dr.-Ing. degree with the highest distinction (summa cum laude) from RWTH Aachen University, Aachen, Germany, in 2019, all in electrical engineering.

Since September 2021, Dr. Cui is with Department of Electrical and Computer Engineering, Seoul National University, Seoul, South Korea as an assistant professor. His research interests include interaction of power systems and power converters, power converters in ac/dc utility applications, and applications of wide-band gap power devices. 

Tutorial Title: Advanced Modulation and Dynamic Control of Dual-Active-Bridge Based Intelligent DC Substation in Flexible Electrical Networks

This talk provides an in-depth discussion and advanced knowledge of modulation and dynamic control of high-power three-phase dual-active bridge (DAB3) dc-dc converters to enhance the operating performance and functionalities of intelligent dc substations in dc-grid applications. With the increasing integration of renewable energies, energy storage systems and the emerging fast charging stations for electric vehicles, dc distributions grids present numerous advantages e.g. higher efficiency, higher power capability and higher flexibility compared to existing ac grids. The key enabling component of flexible dc grids is the intelligent dc substation based on high-power dc-dc converters, which needs to achieve high efficiency over a wide voltage and power range, control the power flow and grid voltage dynamically, and ride through dc short-circuit faults. By employing the asymmetrical duty cycle control method, the soft-switching range of the DAB3 converter is significantly extended over a wide voltage range with a reduced RMS current especially in light-load conditions. Thereafter, this talk also introduces an elegant method to control the transformer winding current and magnetizing flux of the DAB3 converter instantaneously and simultaneously under transient conditions. Thereby, the dc substation can control the power flow dynamically without causing transformer core saturation. Finally, a dc fault ride-through method for the DAB3 converter is explained, which enables the breakerless protection of dc grids. The tutorial will conclude with a Q&A session.

Presenters’  Information

Jingxin Hu, Nanjing University of Aeronautics and Astronautics

Dr. Jingxin Hu is currently a Full Professor at Nanjing University of Aeronautics and Astronautics (NUAA). He received B.S. degree from Northeastern University, China, in 2010, and the M.Sc. degree and Dr.-Ing. degree with summa cum laude from RWTH Aachen University, Germany, in 2013 and 2019, all in electrical engineering. Before joining NUAA in 2022, he was with ABB Corporate Research Center (Switzerland) in 2012 and General Electric Global Research Center (Germany) from 2013-2014. From 2014 to 2022, he was a Senior Scientist and Research Associate at E.ON Energy Research Center, RWTH Aachen. Dr. Hu was the recipient of Prize Paper Award of IEEE IPEC ECCE Asia in 2018. the STAWAG Best Dissertation Prize of RWTH Aachen University in 2019, and IEEE TPEL Outstanding Reviewer Award in 2021. He serves as an Associate Editor for Journal of Power Supply, Technical Program Committee Co-Chair of eGrid 2020, and Session Chairs of IEEE ECCE Asia, PEDG, CIEEC and ISIE. His main research interests include high power converters, intelligent energy routers, renewable power generation and energy storage, as well as dc transmission and distribution.

Tutorial Title: Gallium nitride power transistor reliability and deployment in power electronic systems.

This talk provides an in-depth exploration of the switching reliability of gallium nitride (GaN) power transistors. Gallium nitride (GaN) devices are a necessary technology needed for advancing the efficiency, frequency, and form factor of power electronics. The material composition, architecture, and physics of many GaN devices are significantly different from silicon and silicon carbide devices. These distinctions result in unique stability, reliability, and robustness issues facing GaN power devices. The current understanding of these issues, particularly those related to dynamic switching, and their impacts on system performance from the perspective of a power electronics engineer will be presented. Additionally, the necessary information for deploying GaN devices in the existing and emerging applications, will also be addressed.

Presenters’  Information

Joseph Kozak, Johns Hopkins University Applied Physics Laboratory

Joseph P. Kozak received the B.S. degree in engineering physics and the M.S. degree in electrical engineering from the University of Pittsburgh, respectively, and the Ph.D. degree in electrical engineering from the Center for Power Electronic Systems (CPES), Virginia Tech. Since then, he has been a senior electrical engineer at the Johns Hopkins Applied Physics Laboratory (JHU-APL), and is currently serving as the chief technologist in the spacecraft power engineering group. Joseph’s current research interests include robustness, reliability, and physics of failure of new wide bandgap semiconductors, and their packaging and implementation into high-reliability, power electronic converters and systems. He is a member of IEEE and currently serves as the vice-chair of the IEEE PELS Student and Young Professionals Committee, and chair of the PELS Day Committee.

Tutorial Title: Advances in SiC Power Conversion Technologies for High-Frequency and High-Power Resonant DC-DC Converter Applications

High-frequency and high-power resonant DC-DC converters have been widely used in industrial application such as datacenter, electric vehicle, electrostatic precipitation, medical instruments, DC grid, etc. This tutorial focuses the recent advances of SiC power conversion technologies for high-frequency and high-power resonant DC-DC converters applications. The tutorial starts with the introduction of high-frequency and high-power resonant DC-DC converters including the basics, development history, the state-of-the-art technologies and industrial application trends. Secondly, the electromagnetic modeling and the current uniformity optimization of the multi-chip SiC MOSFET power module are provided in detailed. Then the analysis and suppression methodologies for the crosstalk between paralleled SiC MOSFETs are introduced. The steady-state modeling with phase shift and frequency modulation based on simplified state trajectory, and high accurate binary polynomial model are given. The generic steady-state circuit modeling methodologies for the modular SiC LCC resonant converter with multiple transformers and voltage multipliers are provided. Finally, the technology demonstrator of 50kW 300~500kHz Resonant DC-DC Converter with SiC MOSFET power devices is presented.

Presenters’  Information

Saijun Mao, UniSiC Technology (Shanghai) Co., Ltd., China

Saijun Mao received the B.S. and M.S. degrees from Nanjing University of Aeronautics and Astronautics, Nanjing, China, the Ph.D. degree from Delft University of Technology, Delft, the Netherlands, all in electrical engineering. From 2006 to 2017, he was a senior engineer and project leader with the GE Global Research Center, Shanghai, China. He was also with the Electrical Power Processing group in the department of Electrical Sustainable Energy at the Delft University of Technology, Delft, the Netherlands as a Ph.D. Researcher since December 2014. He was a Professor in Fudan University, China. Now Dr. Mao is with UniSiC Technology (Shanghai) Co., Ltd., China. His research interests include wide-bandgap power semiconductor devices-based power conversion systems, high frequency high voltage generator systems. He has published more than 60 conference and journal papers. He holds over 60 issued patents and pending patent applications. He received one IEEE Best Paper award. He received more than 15 awards in GE Global Research Center.