Guest editorial: Medium‐ and high‐frequency converters for low‐ and medium‐voltage applications

The utilization of distributed renewable energy resources and a focus on clean energy has provided a solution for meeting the growing global energy demand in an environmentally sustainable manner. Furthermore, the goal of achieving net-zero carbon emissions to combat climate change has increased the need to develop new power conversion technologies to integrate zero-emission vehicles and utilize more renewable energy resources. Ongoing research is essential in developing innovative, practical, and highly efficient power interfaces; from low-voltage, high-frequency power supplies to medium-voltage, medium-to-high frequency power converters, to effectively support various emerging power conversion systems, such as residential photovoltaic (PV) systems, electric vehicles, wireless power transfer, energy storage, and utility-scale renewable systems. The next generation of power electronic converters and inverters will be expected to exhibit higher power density, improved reliability, increased compactness, greater efficiency, and reduced costs. Advances in new semiconductor technology, particularly the use of wide-bandgap (WBG) devices, have made the use of WBG devices particularly attractive in low- and medium-voltage power electronic converter systems due to their low on-state resistance, high-voltage blocking capability, high thermal performance, and high-frequency switching characteristic. The emergence of new WBG technology will enable the development of new high-frequency power converters and inverters with a much smaller system footprint, significantly reducing the overall energy conversion system size and weight, resulting in substantial improvements to power density. The purpose of this Special Issue is to promote and document the latest advancements in power electronic converters and inverters that address current challenges in medium- and high-frequency converters for low and medium voltages in order to unlock their potential, expand their range of applications, and accelerate market adoption for industrial and transportation applications. This Special Issue features nine papers, selected through a rigorous peer review process, out of a total of 30 papers submitted for consideration. The theme of the Special Issue is divided into four Topics: Topic A, Dual Active Bridge for Maximum Power Efficiency; Topic B, Wide Bandgap-Based Resonant and Soft-Switching Converters; Topic C, Design, Analysis, and Control of Power Inverters for Low and Medium Voltage Applications; and Topic D, Design and Optimization of Medium Frequency Magnetics. Topic A Dual Active Bridge for Maximum Power Efficiency This Special Issue features papers that address the challenges associated with dual-active bridge converters. ‘Optimal Transformer Design of DAB Converters in Solid-State Transformers for Maximum Power Efficiency’ by Liu et al. presents a methodology for designing the transformer in DAB converters to achieve maximum power efficiency. The optimal number of turns ratio for the transformer is determined by considering the transformer's core loss and copper loss. The optimal number of turns was determined using a finite-element-method-based simulation for resistive and magnetic loss analysis. ‘Suppression of DC-Offset Current in AC-Link of Dual-Active-Bridge DC-DC Converter Based on Triple-Phase-Shift Optimal Control’ by Ren et al. aims to eliminate the DC offset current in the AC link of the dual active bridge. The paper proposes a triple-phase-shift control strategy that can be applied at a wide voltage range. The paper also provides an analysis of the cause and mechanism of DC offset current in the AC link. Using the triple-phase-shift control strategy, both the static and dynamic DC offset current are suppressed, achieved through low-bandwidth detection of the offset current and the planning of the current trajectory. Topic B Wide Bandgap-Based Resonant and Soft-Switching Converters Wide bandgap devices and their applications, including soft-switched converters, provide a key element to unlock high-speed and high-efficiency power conversion. ‘An SiC-Based Soft-Switching & Self-Power Supply MMC for MVDC’ by Zhang et al. examines a high voltage gain modular, non-isolated multilevel converter (MMC) and its control scheme for medium voltage DC (MVDC) distributed systems. Due to the sub-modules structure in this converter, power expansion can be realized with great flexibility. Each sub-module, which consists of the main circuit and the auxiliary cell with a self-power supply, is capable of achieving soft-switching operation. A peak efficiency of 97.3% was demonstrated on a 1.8-kW hardware prototype. ‘Optimal Design of High-Frequency High Efficiency and High-Power Density DC-DC Power Module Based on GaN’ by Lee et al. presents the development of a railway power module that features a wide range voltage input of 60V–160Vdc and a constant voltage output of 24V/10A. The power module utilizes a two-stage topology to achieve voltage conversion. The work employs the most advanced technology in the form of gallium nitride (GaN) as the primary power-switching device. The first stage circuit architecture employs a two-phase interleaved buck converter to convert the wide-range input voltage into a constant intermediate bus voltage (48 V) through closed-loop control. Then, the LLC resonant converter converts the intermediate bus voltage into a constant output voltage through open-loop control. The article provides detailed information about the circuit topology, the selection of power devices, buck converter magnetic integrated coupling inductance, and planar magnetic design. All circuits are integrated into a standard quarter power brick module, and the final prototype achieved 96.1% peak efficiency with 185 W/in3 power density. Topic C Design, Analysis and Control of Power Inverters for LV/MV Applications This Special Issue also delves into the realm of power inverter design, analysis, and control for low- and medium-voltage applications. In particular, He et al.’s article titled, ‘Design and Analysis of a Robust Backstepping Controller for DC Suppression in Parallel UPS Inverter Systems’ proposes an advanced control approach utilizing a non-linear robust backstepping controller to eliminate DC circulating current in parallel UPS systems. The proposed control strategy is implemented in each parallel inverter module to suppress DC component disturbances in the output voltage effectively. Furthermore, the Lyapunov method is employed to guarantee the stability and robustness of the system. In the article titled, ‘11-Level Boost Inverter Topology with Dual-Source Configuration’, Siddique et al. present a novel dual-source configured 11-level inverter topology that utilizes nine power semiconductor devices and one capacitor. The proposed topology boasts a voltage gain of 1.67 by charging the capacitor up to two times the DC input voltage providing a boosting feature. The authors also provide a comprehensive comparison with several other topologies, highlighting the significant contribution of their work. Similarly, in ‘Design of Advanced Aalborg Inverter for Extracting Maximum Power from Renewable Energy Sources Tied with Autonomous Grid System’, Jaisivaa et al. propose a design for an advanced Aalborg inverter that utilizes a reduced number of switches, resulting in enhanced system performance by reducing switching losses. This article investigates a novel buck and boost converter-based inverter operation, which operates at a higher frequency and minimum voltage drop across the inductor, where only one power stage has been applied to enhance the system's reliability and efficiency. In the article ‘Hybrid Cascaded Multilevel Inverters Development for PV-Grid Connection Applications’ by Noman et al., a hybrid cascaded multilevel inverter topology based on a cascaded H-bridge multilevel inverter is presented. The proposed configuration combines two standard multilevel inverters: a cascaded H-bridge and a three-phase cascaded voltage source inverter. The proposed topology employs fewer components for the same voltage level than other traditional topologies, decreasing the voltage stresses on switches. The proposed control scheme effectively maintains the DC link voltage at its reference voltages and provides a power factor at unity while keeping the total harmonic distortion of the grid current within acceptable limits. Topic D Design and Optimization of Medium Frequency Magnetics The optimization of magnetics in power converters operating at high frequencies is crucial for achieving high power density and efficiency. In ‘Integrated Magnetics Optimization Process for an Interleaved Three-Phase Buck Converter at 500 kHz’ by Liu et al., a design and optimization process is presented for a coupled inductor used in a three-phase interleaved buck converter that is part of a two-stage motor drive circuit. The proposed system utilizes wide-bandgap switching devices to minimize switching losses under high-frequency operation and a coupled inductor that integrates three independent inductors to reduce the number and size of magnetic components. The proposed system reduces the coupling coefficient by adding magnetic volume to reduce inductor current ripple, while core loss is reduced by 10.5%. In ‘Comparative Analysis and Improved Design of LLC Inverters for Induction Heating’ by Esteve et al., a comparative analysis and design procedure for a converter based on an LLC resonant inverter used for induction heating applications is presented. The paper aims to determine the inverter design requirements leading to optimal component sizing, improving its operation and minimizing power losses. Additionally, it proposes a design to allow a robust operation of the inverter over a significant range of load impedance variation. The system is verified through hardware implementation where the study results are obtained from testing a 25-kW, 500-kHz converter for induction heating application. Inverter efficiency is obtained at approximately 98.5% using Silicon Carbide MOSFETs. The papers selected for this Special Issue demonstrate a continued advancement in medium- and high-frequency converters. The widespread adoption of medium frequency in power electronics applications is primarily observed in low- and medium-voltage applications. However, this field still poses various challenges that warrant further research, such as reliability considerations, soft-switching techniques, and the application of medium and high frequency in isolated power converters at high power levels. Future research efforts have the potential to unlock the full potential of wide-bandgap devices, high permeability power transformers and wireless power transfer, expand their application, and accelerate market adoption for industrial and transportation applications. Ahmad Elkhateb is a Senior Lecturer (Associate Professor) in power electronics with Queen's University Belfast, Belfast, UK. He leads the power electronics research theme at Queen's University Belfast, as his expertise lies in designing, controlling, and implementing power electronics converters that enable the integration of renewable energy resources. His research interests include microgrids, distributed energy generation, grid integration, and dc-to-dc converters for electric vehicles. Dr Elkhateb was the recipient of the EPSRC New Investigator Award in 2020. He is a Fellow of Higher Education Academy, UK, a Full College Member of the EPSRC, and an Associate Editor for IEEE ACCESS and IET Power Electronics journals. John Lam received his master's and Ph.D. degrees in electrical engineering from Queen's University, Kingston, ON, Canada, in 2006 and 2010, respectively. He is an Associate Professor with the Department of Electrical Engineering and Computer Science, Lassonde School of Engineering, York University, Toronto, ON, Canada. His research interests include power electronics, wide bandgap-based power conversion systems, power management, and renewable energy application. He received the Outstanding Reviewer Award from the IEEE Transactions on Power Electronics in 2018, the Star Reviewer Award from the IEEE Journal of Emerging and Selected Topics in Power Electronics in 2019, and the Lassonde Innovation Early Researcher Award from York University in 2020. He is an Associate Editor of the IEEE Transactions on Power Electronics and a Lead Guest Editor in the IEEE Journal of Emerging and Selected Topics in Industrial Electronics: Special Section on ‘Advanced High Frequency Medium Voltage Power Electronic Systems and Control for Distributed Energy Resources (DER)’. He also served as a Guest Editor in the IEEE Transactions on Industry Applications: Special Issue on ‘Fast, Super Fast And Ultra Super Fast Intelligent and Smart Charging Solutions for Electric Vehicles’ and the IEEE CPSS Transactions on Power Electronics and Applications: Special Issue on ‘Power Quality Conditioning in Modern Power Grids Integrated Emerging Power Electronic Systems’ Hang Seng Che received his B.Eng. degree in electrical engineering from the University of Malaya, Kuala Lumpur, Malaysia, in 2009, and a Ph.D. degree in electrical engineering under the auspices of a dual Ph.D. program between the University of Malaya and Liverpool John Moores University, Liverpool, UK, in 2013. Since 2013, he has been with UM Power Energy Dedicated Advanced Centre, University of Malaya, where he is currently a Senior Lecturer. His research interests include multiphase machines and drives, fault-tolerant control, and power electronics converters for renewable energy applications. He is an Associate Editor of IET Electric Power Applications and Elsevier's Alexandria Engineering Journal. Zhiliang Zhang received his B.Sc. and M.Sc. degrees in electrical engineering from Nanjing University of Aeronautics and Astronautics (NUAA), China, in 2002 and 2005, respectively, and his Ph.D. degree in electrical engineering from Queen's University, Kingston, ON, Canada, in 2009. He is currently a Professor with the Aero-Power Sci-Tech Centre, NUAA. He has authored or co-authored 50 papers in IEEE Transactions on Power Electronics/IEEE Transactions on Industrial Electronics and more than 80 papers in IEEE conferences. His research interest includes high-frequency power conversion with wide bandgap devices. Dr Zhang was a Winner of ‘United Technologies Corporation Rong Hong Endowment’ in 1999. He received the Fok Ying Tung Fund in 2015 and the National Excellent Youth Fund from NSF of China in 2017. He has been serving as an Associate Editor for IEEE Journal of Emerging and Selected Topics of Power Electronics (IEEE JESTPE) since July 2018. He was the Secretary of Power Electronics Society (PELS) on Power and Control Core Technologies from 2013 to 2016. He was a Guest Associate Editor of JESTPE: Special Issue on ‘Resonant and Soft-Switching Techniques with Wide Bandgap Devices’ in 2018 and Special Issue on ‘Power Integration with wide band gap (WBG) Devices and Components’ in 2019.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.