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

In this paper the voltage and current stress of a delta-connection of three single-phase boost-type unity power factor rectifier modules (Δ-Rectifier) is analyzed in order to perform a design comparable to a direct three-phase three-level six-switch unity power factor (conventional) rectifier system. The conduction losses of the power semiconductors are calculated using analytical approximations of the average and rms values of the component currents, the switching losses are taken from previous experimental investigations. Based on this data an overview of the estimated power losses is given for the A-Rectifier as well as for the conventional rectifier for 10kW output power, 800VDC output and 320V/400V/ 480V/530V (rms, line-to-line) mains voltage. These investigations finally lead to efficiency and component count figures. Furthermore, special attention is paid to the control of the whole three-phase system including the DC/DC converter output stages of the line-to-line modules of the A-Rectifier. Finally, topics of the continuation of the research are identified as, e.g., the realization of a prototype in order to verify the theoretical results experimentally also for unbalanced mains voltage conditions and with nonideal components such as nonlinear input inductors employing iron powder cores and the analysis of a A-Rectifier being formed by single-stage SEPIC-type line-to-line modules.

Evaluation of a delta-connection of three single-phase unity power factor rectifier modules (Δ-Rectifier) in comparison to a direct three-phase rectifier realization. Part II - component stress evaluation, efficiency, control

Disclosed is a current source inverter that includes a combination of normally-on and normally-off switches configured to provide free-wheeling paths for current in case of loss of control signals or gate drive power.

Power Converter and Power Conversion Method

Modellierung von Kern- und Wicklungsverlusten

A Wearable Power System (WPS) is a portable power source utilized primarily to power the modern soldier’s electronic equipment. Such a system has to satisfy output power demands in the range of 20 W...200 W, specified as a 4-day mission profile and has a weight limit of 4 kg. To meet these demands, an optimization of a WPS, comprising an internal combustion (IC) engine, permanent magnetic three-phase electrical motor/generator, inverter, Li-batteries, DC-DC converters, and controller, is performed in this paper. The mechanical energy extracted from the fuel by IC engine is transferred to the generator that is used to recharge the battery and provide the power to the electrical output load. The main objectives are to select the engine, fuel and battery type, to match the weight of fuel and the number of battery cells, to find the optimal working point of engine and to minimize the system weight. To provide the second output voltage level of 14 VDC, a separate DC-DC converter is connected between the battery and the load, and optimized for the specified mission profile. A prototype of the WPS based on the optimization presented in the paper results in a total system weight of 3.9 kg and fulfils the mission profile.

Mission Profile Based Optimization of a Wearable Power System

Ultrasonic forces have been used to keep small objects in a suspended state for a long time. In recent years, methods have been developed to manipulate the levitating objects and to lift objects located on acoustically transparent or reflective surfaces. This work demonstrates an ultrasonic levitation system, which is capable of transporting objects from and to acoustically reflective surfaces, while controlling the orientation of the levi-tating object. This requires two different types of piezoelectric transducers operating at two distinct frequencies (25 kHz and 40 kHz), a moveable reflector plate and a novel control method. With these properties, the levitation system presented in this work can be used as a precise contact-less robotic gripper for micro-manufacturing processes of small and fragile objects.

Johann W. Kolar

Papers

Evaluation of a delta-connection of three single-phase unity power factor rectifier modules (Δ-Rectifier) in comparison to a direct three-phase rectifier realization. Part II - component stress evaluation, efficiency, control

Power Converter and Power Conversion Method

Modellierung von Kern- und Wicklungsverlusten

Mission Profile Based Optimization of a Wearable Power System

Contactless Positioning of Objects on Acoustically Reflective Surfaces by Means of Ultrasonic Forces