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.

/pdf/recent-advances-and-industrial-applications-of-multilevel-26fluutoc9.pdf

Recent Advances and Industrial Applications of Multilevel Converters

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

Power electronics

Active three-phase rectifiers operated at switching frequencies of 500 kHz and above, in order to increase their power density, require high-speed current controllers. If these current controllers are implemented purely digitally, which is well established today for 20-200 kHz converter systems, then very high numerical data processing demands result. In this paper, two different types of field-programmable gate arrays (FPGAs) are evaluated for realizing high-speed converter current control. For the implementation of such controllers, not only the FPGA has to be considered but rather the entire signal chain. Two alternative A/D interfaces (including high-speed low-voltage differential signaling data transmission) that are able to handle data sampling rates up to 25 MSa/s are verified. Subsequently, a digital current controller is designed and it is shown how hardware multiplier blocks of modern FPGAs can be used advantageously. Furthermore, the FPGA implementation of high-resolution pulsewidth modulation providing symmetrical pulse patterns for high switching frequencies is described. Measurements taken from a 10 kW VIENNA rectifier laboratory prototype finally demonstrate the high performance of the proposed control concept and show that a low mains current total harmonic distortion of 1.4% can be achieved for such ultrahigh switching frequency converters.

Digital Current Controller for a 1 MHz, 10 kW Three-Phase VIENNA Rectifier

The demand for decreasing cost and volume and also for increasing efficiency leads to a constantly increasing power density of converter systems. For maximizing the power density of a 5 kW telecom supply, an optimization procedure that automatically balances the switching frequency, semiconductor and passive losses, and thermal performance has been developed. This procedure and the belonging analytical converter and transformer models are presented in this paper. Moreover, the resulting optimized design, which has a power density of 10 kW/dm 3 and an efficiency of 94.5% at a height of 1 U, is presented.

Design of a 5-kW, 1-U, 10-kW/dm $^{\hbox{3}}$ Resonant DC–DC Converter for Telecom Applications

In this paper an efficiency optimized variable speed drive is presented. It consists of the alternative 3-level T-type converter topology which is very efficient for low switching frequencies and a standard induction machine. The total system efficiency is optimized concerning the converter losses as well as fundamental and harmonic induction machine losses.

High efficiency drive system with 3-level T-type inverter

Inductive components such as line filter inductors or transformers occupy a significant amount of space in today's power electronic systems, and furthermore, considerable losses occur in these components A main application of filter inductors are EMI filters, as eg employed for the attenuation of switching frequency harmonics of PFC rectifier systems In this paper a design procedure for the mains side LCL filter of an active three-phase rectifier is introduced The procedure is based on a generic optimization approach, which guarantees a low volume and/or low losses Different designs are calculated to show the trade-off between filter volume and filter losses The design procedure is verified by experimental measurements

Optimal design of LCL harmonic filters for three-phase PFC rectifiers

The electrical determination of power losses by measuring the input and output power can reach sufficient accuracy for DC-DC converter systems, if well calibrated voltage meters and shunt resistors are applied. However, it is difficult to determine the power in AC-systems, especially with harmonics, due to phase-errors in the electric measurement. In addition, the electromagnetic interference (EMI) of switched-mode power supplies can disturb the electric power measurement. In this paper, the calorimetric determination of power converter system losses resulting in a high accuracy and which is almost immune against EMI phase errors, is described. The closed-type calorimeter is realized with a double-jacketed chamber which enables the power loss measurement between 10W and 200W for power converter systems of several kW. The resulting deviation of the implemented measurement system is less than ±0.4W, or ±0.05% at full load conditions (several kW), respectively, over the entire measurement range.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/23P4-41_02.pdf

Johann W. Kolar

Papers

Digital Current Controller for a 1 MHz, 10 kW Three-Phase VIENNA Rectifier

Design of a 5-kW, 1-U, 10-kW/dm $^{\hbox{3}}$ Resonant DC–DC Converter for Telecom Applications

High efficiency drive system with 3-level T-type inverter

Optimal design of LCL harmonic filters for three-phase PFC rectifiers

Calorimetric Power Loss Measurement for Highly Efficient Converters