In this paper, an improved control strategy of interlinking converters for hybrid AC/DC microgrid operated in islanding mode is proposed, which applies synchronous generator model to the converters. This enhanced scheme adopts direct frequency control method to realize active power sharing and improves the transient frequency stability by using synchronverter technology. Unlike existing droop control methods of interlinking converters that mostly just focus on power sharing, this scheme can not only maintain proportional power distributed between DC and AC subgrid, but also regulate the AC subgrid voltage directly to improve its poor frequency stability during AC-side loading transitions in autonomous operation. It's noteworthy that this scheme can also keep the AC-side loads working uninterruptedly during AC subgrid faults events by using voltage-controlled method. Moreover, any additional energy storage or inverters are not required to assist interlinking converters for microgrid frequency regulation. The effectiveness of this modified control method is verified by offline time-domain simulation and real-time experiment in MATLAB/Simulink and OPAL-RT digital platform respectively.

Solid-state transformers (SSTs) could serve as interfaces between a medium-voltage (MV) AC grid and a low-voltage (LV) DC load or source, i.e., could be employed in applications with power supply character such as traction auxiliary supplies or rack-level power supplies in future datacenters. For handling the high input-side AC voltage and output side current, SSTs are typically realized as input-series output-parallel (ISOP) arrangements of multiple converter cells, whereby each cell comprises a medium-frequency isolation stage. This paper presents such a multi-cell 25 kW all-SiC MVAC-LVDC SST (6.6 kV AC to 400 V DC) based on the isolated front end (IFE) approach, which is an interesting alternative to the isolated back end (IBE) configuration mainly discussed in literature so far. The IFE concept is briefly explained, the main component stresses are derived, and a converter cell prototype is designed and tested. The 5 kW prototype cell features a power density of 1.5 kW/l (24.6 W/in3) and a measured peak efficiency of 97.5%. This is significantly higher than previously published data for IFE-based SSTs, and in the same range as what has been reported recently for industrial IBE-based SSTs. Thus, this paper confirms that the IFE approach can be a feasible and interesting alternative for realizing MVAC-LVDC SST systems with low complexity.

The Little Box Challenge (LBC) was a competition sponsored by Google and the IEEE Power Electronics Society in 2014-2015, where participants were challenged to design a high power-density single-phase 2 kVA inverter. This paper surveys the designs from eight different participating teams, including academic grant awardees, finalists, and the winners. Inverter topologies, power decoupling circuits, and thermal management strategies are overviewed for each team. Wide bandgap switches were heavily utilized in both the inverter and power decoupling circuits, particularly GaN switches. Most teams utilized a full-bridge inverter with some variations and the most common power decoupling strategy was the use of a synchronous buck converter and a power buffering capacitor. One team used a multi-level inverter approach and a number of teams proposed innovative power decoupling topologies. Heat sinks and active cooling systems, many of which were custom made, were crucial for teams to stay within the 50 °C case temperature limit. The resulting power density of the surveyed teams ranged from 55.8 to 216 W/in3, all of which exceed the 50 W/in3 LBC requirement. This paper surveys the approaches for various teams, shares experimental results from the Taiwan Tech team, and highlights some innovations from the teams that participated in the LBC.

Due to much higher achievable blocking voltage and faster switching speed, power devices based on wide band-gap (WBG) silicon carbide (SiC) material are ideal for medium voltage (MV) power electronics applications. For example, a 15 kV SiC MOSFET allows a simple and efficient two-level converter configuration for a 7.2 kV solid state transformer (SST) for smart grid applications. Compared with multilevel input series and output parallel (ISOP) solution, this approach offers higher efficiency and reliability, reduced system weight and cost by operating at medium to high switching frequency. However, the main concern is how to precisely implement this device in different MV applications, achieving highest switching frequency while maintaining good thermal performance. This paper reviews the characteristics of 15 kV SiC MOSFET and offers a comprehensive guideline of implementing this device in practical MV power conversion scenarios such as AC-DC, DC-DC and AC-AC in terms of topology selection, loss optimization and thermal management.

The investigation shows that power semiconductor devices are the most fragile components of power electronic systems. Improving the reliability of power devices is the basis of a reliable power electronic system, and in recent years, many studies have focused on power device reliability. This paper describes the current state of the art in reliability research for power semiconductor devices, mainly includes failure mechanisms, condition monitoring, lifetime evaluation and active thermal control. Among them, condition monitoring technology are classified and summarized by the failure mechanism and the change rules of characteristic quantities; The method of lifetime estimation is illustrated from the practical point of view; Methods of active thermal control are classified and summarized from the two ideas of reducing loss and loss compensation which are refined by the principle of realization. At last, this paper draws the existing problems and challenges of power devices reliability studies.

With the commercial availability of GaN and SiC-based power semiconductor devices having significantly improved material characteristics, there is a need to discuss the perspective of the underlying physical loss mechanisms of these devices versus their silicon counterparts. This article will compare latest generation Superjunction power transistors versus e-mode GaN HEMTs and SiC MOSFETs in terms of semiconductor losses and their potential for further improvement. A short application section will give practical information on best matching circuits for each device concept.

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 and 2 were published in the December issue last year and the March issue this year respectively, Part 3 appears in this June issue, and the following part is scheduled for the September issue. In Part 3 we are honored to have 4 invited papers. For the first two, each addresses one hot topic in the area of power semiconductor devices: power loss mechanism and reliability. The next two follow up with the state-of-the-arts in the applications of new power semiconductor devices, one application being solid state transformers and the other being single-phase inverters. We begin with a paper on the power loss mechanisms for silicon and wide band-gap power semiconductor devices. It is co-authored by Dr. Gerald Deboy and his team from Infineon Technologies. It presents a detailed comparison between the latest generation Super Junction power transistors and e-mode GaN HEMTs and SiC MOSFETs in terms of semiconductor power losses and their potential for further improvement, with a short application section showing the best matching circuits for each device. The second paper provides a review on the reliability of power semiconductor devices used in power converters.