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

Phase-legs of DC/AC modular multilevel converters (MMC, M2LC) transfer power from the DC input to the corresponding phase output terminal by means of a current that circulates through the DC input and the phase-leg. In addition to the load-dependent DC component required for the power transfer, this circulating current contains significant harmonics if no countermeasures are implemented. Prominently, a large second harmonic appears, essentially because each converter arm performs a single-phase power conversion. This results in higher RMS values of the arm currents and ultimately in higher-than-necessary losses. One option to mitigate these undesired harmonics and the associated losses extends each arm of the MMC by an active filter module that controls the circulating current by injecting a common-mode component into the arm voltage. In this paper, we propose a new variant of an MMC topology with such active filter modules. In contrast to the state of the art, the proposed realization shows lower realization effort: it uses only a single active filter module per MMC phase-leg instead of two, which corresponds to a reduced effort in terms of both, power hardware components and also control and communication electronics. Furthermore, a single active filter module can operate fully self-contained if desired, i.e., without an external communication interface, thus simplifying system integration.

Modular Multilevel Converter Circulating Current Control with Single Active Filter Module per Phase

Silicon carbide (SiC) semiconductors facilitate a considerably lower specific on‐state resistance compared to silicon semiconductors, mainly due to an approximately 10 times higher critical field for avalanche break‐ down, . The performance figure of merit / 2 /3 [ : blocking voltage; : theoret‐ ically achievable value of the specific on‐state resistance of unipolar devices (e.g. Schottky diodes, MOSFETs, JFETs); and : electron mobility and semiconductor’s dielectric constant, respectively] can be used for the purpose of comparison and results in 4 MW/cm for Si and 4000 MW/cm for SiC [1]. On the one hand, the value for the specific on‐state resistance achievable with SiC is approximately the 1000 part compared to that of Si; on the other hand, the blocking voltage achievable with a given chip size and for a given is 30 times higher for SiC. Thus, SiC facilitates the realization of high voltage / high power unipolar semiconduc‐ tor devices that cause low switching losses, due to the absence of storage charge.

Medium-Voltage High-Frequency DC-DC Converter

Experimental verification of an angle-sensorless control scheme for bearingless permanent magnet machines

Drehstromantriebssystem mit motorintegriertem Hochfrequenztrafo zur bidirektionalen Kopplung der Versorgungsspannungen

In this paper, a novel control concept for a unity power factor three-phase AC/DC two-stage telecommunications power supply system is proposed. The system is formed by an input-side delta-connection of three single-phase modules with parallel connected DC outputs. The control concept features output voltage control, module load sharing and mains voltage proportional guidance of the input currents and does allow to continue in operation also in case of heavily unbalanced mains voltage condition like those given for a missing mains phase or in case of an earth-fault of a mains phase or for a short circuit between two mains phases.

A novel control concept for operating a two-stage a-rectifier-based telecommunications power supply module under heavily unbalanced mains voltage conditions

Johann W. Kolar

Papers

Modular Multilevel Converter Circulating Current Control with Single Active Filter Module per Phase

Medium-Voltage High-Frequency DC-DC Converter

Experimental verification of an angle-sensorless control scheme for bearingless permanent magnet machines

Drehstromantriebssystem mit motorintegriertem Hochfrequenztrafo zur bidirektionalen Kopplung der Versorgungsspannungen

A novel control concept for operating a two-stage a-rectifier-based telecommunications power supply module under heavily unbalanced mains voltage conditions