Single-input-multiple-load converter systems sharing a common input DC voltage bus is becoming popular in DC power distribution. Due to the convenience of using conventional voltage-source systems for connecting a common bus voltage with multiple downstream loads, the same configuration is often adopted for current-source systems, where design optimization can be achieved without an intermediate (bus) voltage regulator. However, the stability of such cascaded current-source systems is still relatively unexplored or incomplete, though the associated basic circuit theory has been well established. In this paper, steady-state operating points are obtained by applying power balance between the current-source output converter and the downstream converters. The incremental change of the input power versus the input impedance of the downstream converters is derived. The stability of such current-source converter systems is re-visited using an impedance-based approach. A general set of impedance-based stability criteria is developed and experimentally verified by a DC bus system consisting of a current source output converter and two PWM power converters.

“Sneak Circuit” is defined as the unexpected path or operational status in an electric or electronic circuit due to the limitation or oversight in design by human. The sneak circuit can be triggered to operate under certain conditions, which results in an unwanted or unintended action. As power converter is an artificially designed system, it is undoubted that sneak circuits exist in power converters, while sneak circuit phenomena have been proved in some typical power converters. In order to improve safety and reliability of a power electronic system, it is necessary to understand thoroughly the sneak circuit in power converters under all possible practical conditions. Thus, this paper aims at providing a brief review of sneak circuits in power converters, and summarizes the sneak circuit analysis (SCA) methods based on the graph theory. Finally, some applications on power converters by making use of the SCA principle of sneak circuit analysis are included.

LLC converter has been the simplest topology since long to achieve soft switching and overall the highest performance within small form factor at converter level. This paper discusses the latest advances of LLC converter from the perspective of topology and control. The technology ranges from high current, fast dynamic response to wide operational voltage range. The application mainly falls in the scope of server and data center, and may also cover telecom, PV, battery charging, etc. Index Terms—LLC, review, survey, current sharing, multi-phase, interleave, phase shedding, passive impedance match, SR drive, fast dynamic, current mode control, current sensing, wide voltage range, hold up, high voltage gain.

Due to the increasing power consumption of data centers, efficient dc power distribution systems have become an important topic in research and industry over the last years and according standards have been adopted. Furthermore the power consumed by telecommunication equipment and data centers is an economic factor for the equipment operator, which implies that all parts of the distribution system should be designed to minimize the life cycle cost, i.e. the sum of first cost and the cost of the power conversion losses. This paper demonstrates how semiconductor technology, chip area, magnetic component volumes and switching frequency can be selected based on life cycle cost, using analytical and numerical optimizations. A three-phase buck-type PFC rectifier with integrated active filter for 380V dc distribution systems is used as an example system, which shows that a peak efficiency of 99% is technically and economically feasible with state-of-the-art SiC MOSFETs and nanocrystalline or ferrite cores. Measurements taken on an 8kW, 4kWdm hardware prototype demonstrate the validity and feasibility of the design.

Data centers use more than 1.5% of all electricity in China and the U.S., with continuing growth. This paper reviews the power hierarchy levels within modern data centers. It considers energy consumption and power electronics challenges across all levels of a data center, including building distribution, dc architectures, and conversion down to the board level. Power electronics plays a central role throughout the hierarchy, and emerging approaches are described. Strategies that enhance center energy efficiency, both in terms of overall center operation and in terms of computation performance, are discussed.

with the fast development of power electronics, Power Supplies (SMPS). Nowadays, many researchers have gradually become research focus, which can greatly reduce the value, volume of passive components and help to improve the system power density. However, at such high operating frequency, many challenges have been proposed, such as switching characteristics, topologies characteristics and control methods. This paper starts from the development background of VHF power converters, and an overview of VHF development is described. Different topologies adopted in VHF condition are introduced and compared. At the same time, the resonant driving strategies and control methods for very high frequency converters are discussed and analyzed, which can provide guidance for further research of VHF converters. Index Terms—Very high frequency power converters, topologies, resonant driving, control strategies. I. Introduction With the development of power electronics technique, very high frequency (VHF, 30~300 MHz) power converters have gradually become a hot field of research directions. By increasing the working frequency of the system, the VHF power converters can effectively reduce the volume of the passive components, and improve the power density. Meanwhile, the transmitted and stored energy of components during each operating period can be significantly decreased due to the increase of the frequency. Thus the speed of the transient response can be accelerated. The decrease of the value and volume of passive components is beneficial to the integration and manufacture of the system. The topologies of VHF converters are proposed through a combination of RF power amplifier technology and power electronic technology [1]-[8]. The power amplifier can transform DC components into high frequency AC components, which is similar to the inverter stage of Switching Mode Power Supplies (SMPS). Combining the inverters with the power converter have been proposed [9]-[64], which own excellent characteristics, such as small volume, high power density and fast response speed. Although the VHF system has such merits, the high switching frequency puts forward strict requirements on the selection of semiconductor devices [21]-[28], the utilization of parasitic parameters [29]-[36], the design of the circuit [37]-[42] and the design of passive components [43]-[49]. In the VHF power converters, with the increasement of system switching frequency, switching losses also increase rapidly. Thus, the losses of the switch and the driving circuit must be reduced to ensure a high system efficiency. In the existing VHF power converters, scholars mainly adopt zero voltage switching (ZVS) technology to reduce the power losses caused by the overlap of voltage and current at the instant of switching. Besides, to reduce the driving circuit losses, the resonant driving circuit is also proposed which can utilize the energy stored in the switch input capacitor. Apart from the topologies and the driving methods, another important aspect of VHF converters is the control method. For traditional converters, pulse width modulation (PWM) or pulse frequency modulation (PFM) is used to adjust the drive signal of the system in close-loop control. However, both methods are not available to be adopted in VHF situations. Because in such a high frequency condition, it is difficult to sample and adjust the duty cycle or the operating frequency of driving signals. At the same time, the change of period or duty cycle will affect the operating modes of switches. Thus some suitable control methods have been researched to regulate the output voltage and keep the switch operating in soft-switching modes when the input voltage or load change. In this paper, introduction and detailed analysis of advanced technologies in VHF power converters are presented. Based on existing VHF power converter topologies, the design principle of VHF topology is introduced. The characteristics of different inverter stages, rectifier stages and matching networks are analyzed in Section II. The driving methods of the VHF system are explored in Section III. An overall analysis and comparison of the self-resonant driving circuit and multi-resonant driving circuit are given. The control strategies of VHF power converter are discussed in Section IV. Section V elaborates the opportunities and challenge.

Electrical drives are one of the major consumers of electrical energy and their penetration in the market is still growing. Hence, for many drive applications efficient, reliable and cost effective solutions have to be found. Switched reluctance drives (SRD) offer a potential solution when focus is mainly on cost and robustness. However, to benefit from the unique advantages of this machine type a deep understanding of its strongly non-linear behavior is required. After discussing some major differences to classic rotating field machines, this paper presents a broad overview of the state of the art of SRD taking into consideration all aspects relevant to machine modeling, design and control development process. Finally, applications on the market utilizing SRDs and the focus of current research is presented. After reading this paper the reader will be able to assess if this modern drive technology could be advantagous in a given application.

Modern society has reached a point where virtually every crucial economic and social function depends on the secure and reliable operation of the electrical power and energy infrastructures. The energy consumption growth and the population growth are pushing world's total energy consumption to double by 2050. This represents grand challenges and opportunities for power electronics and electric power systems engineers to modernize the power grid. Power electronics & systems (PEAS) technology is increasingly important for smarter distributed systems, particularly for power grid modernization. This paper discussed smart technology solutions, such as PEAS, for the changing nature of the electric power system. Specific technical challenges that are facing the power electronics and electric power systems communities are then elaborated. It is shown that we can meet the grand energy challenge by leveraging the grid modernization efforts. To provide electric power to twice as many people does not have to increase the required environment footprint.

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 was published in the December issue last year, Part 2 appears in this March issue, and the following parts are scheduled for the next issues. In Part 2 we are honored to have 8 invited papers. For the first 3, each addresses one hot topic respectively in one of the 3 major application areas of power electronics: electric power grid, motor drives, and power supplies. The next 3 follow up with the state-of-the-arts in the structure or converters that are adopted in data center power systems, while the last 2 discuss specific issues for general power electronic circuits and systems. We begin with a paper on the modernization of electric power grid. It is co-authored by Dr. Don Tan and Dr. Damir Novosel representing leadership of IEEE Power Electronics Society and IEEE Power and Energy Society respectively. It presents how power electronics & systems (PEAS) technology could possibly provide smart technology solutions for the power grid modernization to meet the grand energy challenge. Digital Object Identifier 10.24295/CPSSTPEA.2017.00001