Power electronics is the enabling technology for optimizing energy harvesting from renewable systems like Photovoltaic (PV) and wind power systems, and also for interfacing grid-friendly energy systems. Advancements in the power semiconductor technology (e.g., wide band-gap devices) have pushed the conversion efficiency of power electronics to above 98%, where however the reliability of power electronics is becoming of high concern. Therefore, it is important to design for reliable power electronic systems to lower the risks of many failures during operation; otherwise will increase the cost for maintenance and reputation, thus affecting the cost of PV energy. Today's PV power conversion applications require the power electronic systems with low failure rates during a service life of 20 years or even more. To achieve so, it is vital to know the main life-limiting factors of power electronic systems as well as to design for high reliability at an early stage. Knowhow of the loading in power electronics in harsh operating environments (e.g., fluctuating ambient temperature and solar irradiance) is important for life-time prediction, as the prerequisite of Design for Reliability (DfR). Hence, in this paper, the technological challenges in DfR of power electronics for grid-connected PV systems will be addressed, where how the power converters are stressed considering real-field mission profiles. Furthermore, the DfR technology will be systematically exemplified on practical power electronic systems (i.e., grid-connected PV systems).

Although non-radiative wireless power transfer (WPT) was invented over a century ago, it has regained research and development interests in 1980s. Over the last 15 years, WPT has appeared as an “emerging” technology that has attracted wide-spread attention in both academia and industry. Because of the long history of WPT research and developments, researchers of the modern days often do not know some historical milestones of WPT. This paper aims at providing a brief history of some key concepts and technologies that pave the way for modern WPT research and applications. A few misconceptions of WPT technologies are particularly highlighted so that new researchers entering this research field can avoid such pitfalls. Finally, some discussions on present and future trends of WPT are included.

Availability is an important factor to be considered when designing wind turbine generator systems. The quest for increased availability is based on the following five design approaches - design for component reliability, active control for reliability, design for fault tolerance, prognostics, and design for maintainability. This paper reviews methods focussing on the first three, i.e. component reliability, active control, and fault tolerance. The paper further identifies some promising directions for further research.

Rapidly decreasing prices for renewable energy, increasing industrialization and electrification of the global economy, and a world-wide focus on reducing carbon emissions, is causing a reexamination of the power system of the future. A reliance on centralized planning and control, scheduled and dispatched generation, and unidirectional power flows, allowed the design of a robust and scalable power system, that did not require dynamic controls infused into the grid. As a result, the existing grid, the most complex machine built by man, has been the driver of sustained global economic growth for well over a century. Increasing levels of variable and non-dispatchable renewable energy resources mixed into the grid, bidirectional power flows resulting from a dramatic increase in the number of prosumers (‘producer + consumer’), are adding complexity, volatility and economic inefficiency to grid operations, making grid control with conventional centralized technologies very challenging. This paper looks at the role that distributed power electronics could play in the grid of the future, allowing a cost-effective approach to grid control that can help achieve global objectives of operating with high renewable penetration.

In a hybrid IGBT module with SiC diodes as free-wheeling diodes, high frequency oscillation occurs during turn-on due to the fast switching transient of SiC diode and the resonance between circuit parasitic inductances and the junction capacitance of SiC diode. Such oscillation causes EMI noise which may affect the performance of the system. Methods to mitigate the turn-on oscillation are studied. Firstly, the effect of gate drive parameters on turn-on oscillation is investigated with respect to different gate voltages and gate charging currents. Then a novel turn-on oscillation suppression method is proposed with combination of damping circuit and active gate driver. The proposed oscillation suppression method can achieve the lowest EMI noise while remaining the advantage of lower switching loss brought by SiC diodes. Detailed theoretical analysis of the turn-on oscillation is conducted, and experimental results are given to verify the effectiveness of the proposed oscillation suppression method.

This paper describes the 750-Vdc, 100-kW, 20-kHz bidirectional isolated dual-active-bridge (DAB) dc-dc converters using four 1.2-kV 400-A SiC-MOSFET dual modules with or without Schottky barrier diodes (SBDs). When no SBD is integrated into each dual module, the conversion efficiency from the dc-input to the dc-output terminals is accurately measured to be 98.0% at the rated-power (100kW) operation, and the maximum conversion efficiency is as high as 98.8% at 41-kW operation, excluding the gate-drive and control-circuit losses from the total power loss. The bidirectional isolated DAB dc-dc converters are so flexible that series and/or parallel connections of their individual input and output terminals make it easy to expand the voltage and current ratings for various applications such as the so-called “solid-state transformer” or “power electronic transformer.”

This paper overviews the silicon carbide (SiC) technology. The focus is on the benefits of SiC based power electronics for converters and systems, as well as their ability in enabling new applications. The challenges and research trends on the design and application of SiC power electronics are also discussed.

In today’s power electronics products, quality and reliability are given. Great emphases are placed on high efficiency, high power density and low cost. With recent advances made in gallium nitride power devices (GaNs), it is expected that GaNs will make significant impacts to all three areas mentioned above. Thanks to the absence of reverse recovery charge and smaller junction capacitances, the turn-on loss of GaN is significantly reduced and Turn-off loss and driving loss are negligible, for the first time. These desired properties coupled with ZVS techniques will drastically reduce all switching related losses, thus enabling GaN to operate at a switching frequency more than ten times higher than its silicon counterparts. To illustrate the impact of GaN on efficiency, density and even design practice, a 1 kW server power supply is demonstrated which employs an interleaved CRM totem-pole PFC followed with an LLC resonant converter. Both operate beyond 1 MHz. All magnetic components are integrated into PCB with much reduced EMI noises, thus, only a simple one-stage EMI filter is required. The system achieves a power density more than 150 W/in³, an efficiency above 96%, and much improved manufacturability with minimum labor content.

With this editorial, we sincerely welcome our readers to the brand-new publication — CPSS Transactions on Power Electronics and Applications (CPSS TPEA). It is sponsored and published by China Power Supply Society (CPSS) and technically co-sponsored by IEEE Power Electronics Society (IEEE PELS). CPSS was founded in 1983 and has been the only top-level national academic society in China that solely focuses on the power supply/power electronics area. In the past 30-plus years CPSS has dedicated to provide to its members, researchers, and industry engineers nationwide with high quality services including conferences, technical training, and various publications, and this in deed has helped the society build up its membership rapidly, which now totals up to more than 4000 individual members plus 500 enterprise members. The fast growth of membership in turn compels CPSS to always work out better services for its members, one of which being the open-up of this periodical — a new journal in English language as a publication platform for international academic exchanging. This of course needs to be done through international cooperation, and that’s why IEEE PELS is tightly involved, being the premier international academic organization in power electronics area and one of the fastest growing technical societies of the Institute of Electrical and Electronics Engineers (IEEE). To fulfill the publishing need of the fast-developing power electronics technology worldwide is a more important purpose of launching this new journal. So far there are only 3 or 4 existing journals which are concentrated on power electronics field and have global reputation. For quite a few years people in the international power electronics community have had the feeling that, the existing journals have not even come close to meeting the huge demand of global academic and technology exchanges. E.g., the two existing IEEE power electronics journals, i.e. IEEE Transactions on Power Electronics (IEEE TPEL) and IEEE Journal of Emerging and Selected Topics in Power Electronics (IEEE JESTPE), now publish about 1000 papers a year, which is under a very low paper acceptance rate of around 25%, but still have a back-log of about one year for the newly accepted papers to finally appear in printed form to the public. The addition of this new dedicated journal would be an ideal improvement to fulfill such a tremendous need. The booming of publishing need really is an indicator of how fast power electronics has been developing in recent years. Innovations have been continuously coming up from component (both active device and passive device), module, circuit, converter, to system level, covering different technical aspects as topology or structure conceiving, modeling and analysis, control and design, and measurement and testing. New issues and corresponding solutions have been continuously presenting as the applications of power electronics prevail horizontally in almost every area and corner of human society, from industry, residence and commerce, to transportations, and penetrate vertically through every stage of electric energy flow from generation, transmission and distribution, to utilization, in either a public power grid or a stand-alone power system. I personally believe that we are entering a world with “more electronic” power systems. The prediction around 30 years ago, that power electronics one day will become one of the major poles supporting the human society, is coming into reality. And I also believe, that power electronics is going to last for long time as an important topic since it is one of the keys to answer a basic question for human society, which is how human can harness energy more effectively and in a manner friendlier to both the user and the environment. Therefore, I assume that there is probably no better fitting as for CPSS TPEA to publish its first few issues under a special topic about the developing trends of power electronics. We have invited a group of leading experts in different areas of power electronics to write survey/review papers or special papers with review/overview nature to some extent. To publish in a timely and regular style, we organize this inaugural Special Issue into different parts. Part 1 is in this issue and the other parts will appear in the following issues. In Part 1 we are honored to have 8 invited papers. The first 4 address the state-of-the-arts application techniques of new power semiconductor devices and modules based on GaN or SiC and how these devices can be adequately used to improve the performance of converters and systems, while the rest 4 discuss the developing trends of different aspects of some currently hot or future promising application areas. We begin with a review paper on the application of GaN devices for 1kW server power supply with integrated magnetics. It is written by Dr. Fred C. Lee and his research group from Virginia Polytechnic Institute and State University. It presents how GaN devices coupled with soft-switching techniques drastically reduce power losses and enable a switching frequency more than ten times higher than silicon devices, with much reduced EMI noises. The second paper overviews the silicon carbide (SiC) based power conversion technology from device level up to system and application level. It is written by Dr. Fred (Fei) Wang and his research group from the University of Tennessee. The focus of this paper is on the benefits of SiC based power electronics for converters and systems, as well as their ability in enabling new applications. The third paper is about a specific application of SiC-MOSFET dual modules to bidirectional isolated dual-active-bridge (DAB) DC-DC Converters. It is written by Dr. Hirofumi Akagi and his research group from Tokyo Institute of Technology. It illustrates how SiC-MOSFET is adopted to improve the efficiency and modular expandability of bidirectional isolated DAB DC-DC converter. The fourth paper is regarding how to suppress turn-on oscillations for hybrid power modules combining Si IGBTs and SiC diodes. It is written by Dr. Dehong Xu and his research group from Zhejiang University in cooperation with Fuji Electric Co., Ltd.. The paper reviews the causing, effect, and recently published damping methods of high frequency oscillation occurring during turning-on transients of Si IGBT and then proposes a novel suppression method. The fifth paper is written by Dr. Deepak Divan and his research group from Georgia Institute of Technology, discussing the applications of power electronics to the future grid. It looks at the role that distributed power electronics could play where increasing levels of variable and non-dispatchable renewable energy resources are mixed into the grid and bidirectional power flows are adding complexity to grid operations. The sixth paper is written by Dr. Jan A. Ferreira and his research group from Delft University of Technology, discussing wind turbine generator systems — another important application area of power electronics. It provides a comprehensive review and future trends prediction on how the availability of wind turbine generator system could be increased through appropriate design and control for reliability and fault tolerance. The seventh paper is written by Dr. S.Y. Ron Hui from the University of Hong Kong and Imperial College London, about a recently emerging application area of power electronics — non-radiative wireless power transfer (WPT). The paper briefly reviews the history of some key concepts and techniques and particularly highlights a few misconceptions of WPT, and supplies the author’s view on the present and future trends. Last but not least, the eighth paper is written by Dr. Frede Blaabjerg and his research group from Aalborg University, about a very hot application area of power electronics for the past years — grid-connected photovoltaic systems. The paper focuses on design for reliability (DfR) and it summaries in detail the technological challenges in DfR of power electronics with a systematic exemplification. I’d like to thank the authors of all these 8 invited papers. It’s their high-quality contributions that finally leads to the launching of this new journal. I’d like to thank Dehong Xu, President of CPSS, who in 2015 initiated the idea of publishing the new journal and since then has been persistently supporting my work as the founding Editor-in-Chief. I’d also like to thank Jiaxin Han, Secretary General of CPSS, Jan A. Ferreira, President of IEEE PELS, 2015-2016, Don F.D. Tan, President of IEEE PELS, 2013-2014, and Frede Blaabjerg, IEEE PELS Vice President for Products, 2015-2016, who form the CPSS and IEEE PELS Joint Advisory Committee for our new journal with Dehong Xu and myself. Other IEEE officers and leading staffs like Dushan Borojevich, PELS President, 2011-2012, Alan Mantooth, PELS President, 2017-2018, Mike Kelly, PELS Executive Director, and Frank Zhao, Director of China Operations, IEEE Beijing Office, just to name a few, also provided continuous support and constructive advices. My earnest thanks also go to the CPSS Editorial Office led by Lei Zhang, Deputy Secretary General of CPSS, for their wonderful editing work. It would not have been possible to create a new journal in such a short time without their efforts. I’d like to finally thank all the members of the Standing Council of CPSS and particularly the leaders of Chinese power electronics industry. They always firmly stand behind CPSS TPEA and ready to help whenever needed.