There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Multilevel inverters: a survey of topologies, controls, and applications

Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

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Recent Advances and Industrial Applications of Multilevel Converters

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

Eine Schalteinrichtung zum Schalten eines Stromes zwischen einem ersten Anschluss (1) und einem zweiten Anschluss (2) weist eine Serienschaltung von mindestens zwei JFETs (J1-Jn) auf, mit weiteren JFETs (J2-Jn), die zu einem untersten JFET(J1) in Serie geschaltet sind, und wobei ein Beschaltungsnetzwerk zur Stabilisierung der Gatespannungen der JFETs (J1-Jn) zwischen dem zweiten Anschluss (2) und dem esrsen Abschluss (1) geschaltet ist. Dabei ist zwischen Gateanschlussen (GJ2,GJ3... GjN) der weiteren JFETs(J2-Jn) und dazugehorogen Kathodenanschlussen von Dioden (DAV) des Beschaltungsnetzwerkes jeweils eine Zusatzschaltung (5) geschaltet, welche beim Einschalten und im eingeschalteten Zustand das Potential des jeweiligen Gateanschlusses hoher halt als jenes des dezugehorigen Sourceanschlusses.

Schalteinrichtung mit jfet-serieschaltung

Future three-phase ac-dc converter systems ideally allow for bidirectional power flow, provide high-frequency isolation, and feature buck-boost capability. Further, high efficiency and high compactness and the applicability of standard half-bridge and/or three-phase full-bridge (B6) semiconductor arrangements are crucial aspects. This Paper proposes a novel converter concept that employs B6-type circuits on the input and on the output side and a low-complexity Discontinuous Conduction Mode (DCM)-type or a Dual Active Bridge (DAB)-type modulation strategy, thereby enabling single-stage isolated three-phase ac-dc power conversion with sinusoidal grid currents and controlled dc output voltage. The converter operation is detailed on the switching-frequency and on the grid-frequency time scale and verified by means of circuit simulations. The converter control characteristic and the main power component stresses are discussed and design guidelines for a 6.6 kW prototype system with an expected efficiency $\eta > 98\%$ are presented. Finally, an outlook on future research related to the practical realization and advanced modulation of the topology is provided.

Novel Bidirectional Single-Stage Isolated Three-Phase Buck-Boost PFC Rectifier System

A recently introduced Dual Three-Phase Active Bridge Converter (D3ABC) provides two three-phase ac ports (ac<inline-formula><tex-math notation="LaTeX">${}_{1}$</tex-math></inline-formula> and ac<inline-formula><tex-math notation="LaTeX">${}_{2}$</tex-math></inline-formula>), two dc ports (dc<inline-formula><tex-math notation="LaTeX">${}_{1}$</tex-math></inline-formula> and dc<inline-formula><tex-math notation="LaTeX">${}_{2}$</tex-math></inline-formula>), and galvanic isolation between the ports ac<inline-formula><tex-math notation="LaTeX">${}_{1}$</tex-math></inline-formula>, dc<inline-formula><tex-math notation="LaTeX">${}_{1}$</tex-math></inline-formula> (primary side) and ac<inline-formula><tex-math notation="LaTeX">${}_{2}$</tex-math></inline-formula>, dc<inline-formula><tex-math notation="LaTeX">${}_{2}$</tex-math></inline-formula> (secondary side). Previously documented studies confirm that the D3ABC is generally capable of transferring power between all four ports. However, it has been found challenging to operate the converter if ac voltages with different line frequencies, <inline-formula><tex-math notation="LaTeX">$f_{1} \ne f_{2}$</tex-math></inline-formula>, are present at the ports ac<inline-formula><tex-math notation="LaTeX">${}_{1}$</tex-math></inline-formula> and ac<inline-formula><tex-math notation="LaTeX">${}_{2}$</tex-math></inline-formula>. Such operation causes Low-Frequency (LF) power pulsations in the converter's dc links, leading to fluctuating dc link voltages and distorted phase currents. In this paper, a new duty-cycle dependent phase shift modulation scheme is proposed that eliminates such LF power pulsations and substantially increases the theoretical maximum transmittable power between primary and secondary sides compared to previous work. The new modulation scheme is developed on the basis of analytical considerations, which are supported by the results of numerical calculations, and verified by means of circuit simulations and experimental results. A hardware demonstrator originally designed for a rated power of <inline-formula><tex-math notation="LaTeX">$\text{8}\,$</tex-math></inline-formula>kW when operated from ac<inline-formula><tex-math notation="LaTeX">${}_{1}$</tex-math></inline-formula> to dc<inline-formula><tex-math notation="LaTeX">${}_{2}$</tex-math></inline-formula> at the European low-voltage ac mains (<inline-formula><tex-math notation="LaTeX">$V_{\mathrm{ac,1}} = \text{230}\,{\rm V}$</tex-math></inline-formula> line-to-neutral rms, <inline-formula><tex-math notation="LaTeX">$V_{\mathrm{dc,1}} = \text{800}\,{\rm V}$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$V_{\mathrm{dc,2}} = \text{400}\,{\rm V}$</tex-math></inline-formula>) is used for experimental verification. Since the operation with <inline-formula><tex-math notation="LaTeX">$f_{1} \ne f_{2}$</tex-math></inline-formula> leads to an increase of the currents in the converter, the experimental verification is conducted at half voltages and for a reduced power of <inline-formula><tex-math notation="LaTeX">$\text{2}\,$</tex-math></inline-formula>kW that is transferred from ac<inline-formula><tex-math notation="LaTeX">${}_{1}$</tex-math></inline-formula> to ac<inline-formula><tex-math notation="LaTeX">${}_{2}$</tex-math></inline-formula> at substantially different primary-side and secondary-side line frequencies of <inline-formula><tex-math notation="LaTeX">$f_{1} = \text{50}\,$</tex-math></inline-formula>Hz and <inline-formula><tex-math notation="LaTeX">$f_{2} = \text{77}\,$</tex-math></inline-formula>Hz. The measured results agree well with the simulated results. In particular, the dc link voltages show almost constant waveforms, which confirms the correct operation of the proposed modulation scheme.

https://ieeexplore.ieee.org/ielx7/8782709/8932554/09915373.pdf

Duty-Cycle Dependent Phase Shift Modulation of Dual Three-Phase Active Bridge Four-Port AC–DC/DC–AC Converter Eliminating Low Frequency Power Pulsations

In this paper, we describe a development of an interactive educational tool in Circuits and Systems (iCASS) and its introductory effect to the College of Technology. The purpose of this tool is to help teacher’s lecture and student’s self-learning. This tool can be used for on-line learning, can be easily integrated into an E-Learning platform for distance learning, and can be used in the classroom with notebook computer and over-head projector, via Internet or CD-ROM. For the purpose of implementation, we produce a set of teaching materials using HTML text and Java Applets for interactive animation. As a result, the proposed tool can be used as a self-learning tool independent of time and working place. Moreover, in this tool, the movement of the engineering model isn’t only seen, but hearing as sound is also very effective in study. Futhermore, this tool might be canceled ”squiffy doo” of the simulation by connecting an actual model and computer. We describe that the proposed tool has an effect for interest attachment to students and allow to speed up the learning process. The E-Leaning tool as presented at the conference can be found at http://www.sia.co.jp/˜icass/index.html.

Development of an Interactive Circuits and Systems Seminar (iCASS) and its effectiveness

A multiphase converter topology is used to transmit electrical energy from an AC voltage input (25) having m mains phase connections (28) to a DC voltage output (26) or vice versa. It has a power section (21) having half-bridges (211, 212, 213) for switching currents, an AC voltage filter (22) connected between the power section (21) and the AC voltage input (25), and one or more DC voltage blocks (23) connected between the power section (21) and the DC voltage output (26). The AC voltage filter (22) has at least one AC voltage filter stage (221, 222, 223) with m+1 input connections, m+1 output connections and an earthing connection. In this case, the m mains phase connections (28) are connected in parallel with one another and form a first phase connection for connecting a single-phase AC voltage, and a neutral conductor connection of the AC voltage filter forms a neutral conductor connection (27) of the AC voltage input (25) and a second phase connection for connecting the single-phase AC voltage.

Johann W. Kolar

Papers

Schalteinrichtung mit jfet-serieschaltung

Novel Bidirectional Single-Stage Isolated Three-Phase Buck-Boost PFC Rectifier System

Duty-Cycle Dependent Phase Shift Modulation of Dual Three-Phase Active Bridge Four-Port AC–DC/DC–AC Converter Eliminating Low Frequency Power Pulsations

Development of an Interactive Circuits and Systems Seminar (iCASS) and its effectiveness

Multiphase converter topology for multiphase and single-phase operation