Hangzhou, China zpec@zju.edu.cn
Hangzhou, China zpec@zju.edu.cn
Recent Advancements on Active Flux Control and DC Bias Prevention of Transformer Magnetic Core in AC-DC and DC-DC Applications
Power transformers, operating on the fundamental principles of magnetic flux coupling, are vital components spanning traditional line-frequency applications to modern high-frequency isolated DC-DC topologies, such as dual-active-bridge (DAB) converters. However, the presence of a DC bias in the magnetic flux—under either steady-state or transient conditions—severely degrades transformer performance. This phenomenon leads to core saturation, reduced efficiency, severe acoustic noise, mechanical vibration, and destructive inrush currents.
This tutorial presents recent advancements in the modeling, analysis, and active control of magnetic flux in power transformers. By actively regulating the flux trajectory, DC bias can be effectively eliminated across all operating regimes, inherently preventing transient inrush currents. Furthermore, this session will cover closed-loop control strategies for power semiconductor stacks to actively demagnetize and remove residual flux in cores featuring hard magnetic materials. Complementing these control-centric approaches, the tutorial will introduce novel, DC-current-tolerant power transformer designs tailored for high-power conversion. These innovations equip converter stations with critical ancillary functionalities without sacrificing footprint or incurring extra hardware costs.
Finally, the practical deployment and systemic benefits of these techniques will be comprehensively explored across a variety of critical applications. These include accelerated black-start restoration utilizing grid-forming (GFM) inverters, high-frequency DAB converters, converter stations within bipolar medium-voltage DC (MVDC) distribution networks, STATCOMs, and Enhanced STATCOMs (E-STATCOMs).
Shenghui Cui
Seoul National University
Shenghui Cui (Senior 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, where he is currently an associate professor. From March 2015 to May 2021, he has been with the Institute for Power Generation and Storage Systems, E.ON Energy Research Center, RWTH Aachen University, Aachen, Germany, where he worked as research associate and later on senior scientist. Dr. Cui was the recipient of the STAWAG Best Dissertation Prize from Faculty of Electrical Engineering and Information Technology, RWTH Aachen University in 2019, the Second Place Prize Paper Award of the IEEE Transactions on Power Electronics in 2018, and Best Paper Award of IEEE PEDG in 2025, the Second Prize Paper Award of IEEE IPEC (ECCE Asia) in 2018, and the Outstanding Presentation Award of the IEEE Applied Power Electronics Conference in 2014. Dr. Cui has experience of instructing tutorials in various international conferences in the field of power electronics, including IEEE eGrid 2020, IEEE IPEMC ECCE Asia 2020, IEEE ECCE 2021, ICEE 2022, IEEE ECCE 2022, IEEE ICPE 2023, IEEE SYPS 2023, IEEE IPEMC ECCE Asia 2024, and IEEE ICDCM 2026.
Outline and Schedule (3-hour duration)
| Duration | Topic | Presenter |
|---|---|---|
| 20 min | Section 1: Basics of three-phase transformers | Shenghui Cui |
| 60 min | Section 2: Residual flux demagnetization and soft magnetization | Shenghui Cui |
| 10 min | Break | — |
| 45 min | Section 3: Dynamic flux control of dual-active bridge (DAB) converters | Shenghui Cui |
| 45 min | Section 4: DC-current-tolerant power transformers | Shenghui Cui |
| 15 min | Q&A and Open Discussion | Shenghui Cui |
Section 1 – Basics of three-phase transformers (20 min)
Section 2 – Residual flux demagnetization and soft magnetization (60 min)
Section 3 – Dynamic flux control of dual-active bridge (DAB) converters (45 min)
Section 4 – DC-current-tolerant power transformers (45 min)
