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

Future electric vehicle chargers should feature full nominal output power in single-phase (1-Φ) and three-phase (3-Φ) operation, such that they can be employed in the USA as well as in Europe. Further, the converter system should have buck-boost capability to cover a wide DC output voltage range in order to provide compatibility with various nominal battery voltage levels. The phase-modular Y-Rectifier consists of three buck-boost converter modules, features unity power factor operation and allows for an ultra-compact and highly efficient converter realization, where so far only 3-Φ operation was investigated in literature. In this paper, circuit extensions adapting the Y-Rectifier for both 1-Φ and 3-Φ operation are analyzed and comparatively evaluated, where also a new six-module Y-Rectifier (6M-YR) topology is proposed. The required modulation and control techniques of the 6M-YR are presented for 1-Φ and 3-Φ operation. The discussed topologies are then compared by means of a component current conduction stress and a power stage performance analysis for a 6.6 kW, 3-Φ 400 V (Europe) 1-Φ 240 V (USA) AC, 200 V to 750 V DC application. Further, EMI filter design guidelines for the 6M-YR are presented. The results indicate the feasibility of a highly compact CISPR 11 Class B compliant 6M-YR with a power density of 10 kW/dm3 (164 W/in3) and a nominal efficiency of 98.1 % in 3-Φ and 97.6 % in 1-Φ operation.

Single-Phase Full-Power Operable Three-Phase Buck-Boost Y-Rectifier Concepts

Stabilization of the position and orientation of non-spherical, sub-wavelength particles in mid-air is required for using acoustic levitation forces in applications such as automation of micro manufacturing processes, 3-D scanning, and inspection. Acoustic locking has previously been demonstrated by time-multiplexing of different acoustic traps at the same frequency. In this case, the magnitude of the acoustic levitation forces and the stabilizing torque are coupled by the ratio of the durations during which the different traps are applied and cannot be adjusted independently assuming operation at maximum power. This work presents a compact device that uses a method for independently adjusting the vertical trapping forces and the stabilizing torque using two different ultrasonic frequencies. A 40-kHz vertical standing wave is used to generate levitation forces that counteract the gravitational force. Additionally, a 25-kHz horizontal standing wave is used to generate a tunable stabilizing torque. Using this method, objects made from high-density materials across a wide range of geometries can be locked acoustically with increased stability compared with state-of-the-art methods. This is demonstrated by locking tin cuboids with a density of 7.3 g/cm3 and plastic cuboids with average side lengths between 0.9 and 3.5 mm. The experimental results demonstrate torsional spring constants of up to 50 nN $\cdot $ m/rad and an orientation stability of <7.5°.

Multi-Frequency Acoustic Levitation and Trapping of Particles in All Degrees of Freedom

Die vorliegende Erfindung schafft eine galvanisch getrennte Ubertragung elektrischer Energie zwischen drei Spannungssystemen. Hierzu ist ein Transformator vorgesehen, welcher insgesamt funf Wicklungen umfasst. Durch gezieltes Ansteuern der einzelnen Wicklungen kann dabei die Ubertragung zwischen den einzelnen Spannungssystemen gesteuert werden.

Transformator für einen Dreiport-Spannungswandler, Dreiport-Spannungswandler und Verfahren zum Übertragen von elektrischer Energie

Variable speed drives (VSDs) for electric motors are a foundational component of global electrification, with electric motors consuming 45% of global electricity. Conventional three-phase buck–boost inverter topologies have substantial low-frequency current stresses in the buck–boost inductor, driving size, losses, and cost in VSD systems. In this letter, we propose a novel circuit topology for phase-modular three-phase buck–boost inverter systems based on the four-switch noninverting buck–boost concept, which we call the return path inductor Y-inverter (RPI-YI). By relocating the buck–boost inductors from the forward current path to the return path, the RPI-YI concept reduces the inductor rms and peak current stresses by up to <inline-formula><tex-math notation="LaTeX">$90 \%$</tex-math></inline-formula> compared to a conventional topology, resulting in a potential magnetics volume reduction of <inline-formula><tex-math notation="LaTeX">$80 \%$</tex-math></inline-formula>. The RPI-YI concept, therefore, supports more compact, efficient realizations of modular buck–boost VSD systems.

New Return Path Inductor Buck–Boost Y-Inverter Motor Drive With Reduced Current Stresses

The present invention relates to systems, methods and apparatus for the parallel operation of electronic power switches (3, 4) with negative temperature coefficient of the forward voltage or wide tolerance of the switching threshold voltages

Johann W. Kolar

Papers

Single-Phase Full-Power Operable Three-Phase Buck-Boost Y-Rectifier Concepts

Multi-Frequency Acoustic Levitation and Trapping of Particles in All Degrees of Freedom

Transformator für einen Dreiport-Spannungswandler, Dreiport-Spannungswandler und Verfahren zum Übertragen von elektrischer Energie

New Return Path Inductor Buck–Boost Y-Inverter Motor Drive With Reduced Current Stresses

A method and apparatus for parallel operation of electronic power switches