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

Solid state pulsed power systems containing IGBT switches are mainly operating with input voltages between 400 V and 3 kV depending on the maximum allowable blocking voltage of the IGBTs. Nevertheless, high output voltages of several kilovolt can be achieved for example by the use of a pulse transformer, a Marx generator configuration or a combination of both. The pulse power (e.g. 20MW) is normally provided from a capacitor bank whereas the average power (here 25kW) is supplied by a converter connected to the mains, whose line to line voltage can vary from 177 V to 528 V world wide. Depending on the ratio of the mains to the capacitor bank voltage the converter has to work in a buck or boost mode. Additionally, due to the possible high repetition rate of pulse modulators (500-1000Hz) the capacitor bank has to be recharged before the next pulse is generated, which would demand a high dynamic voltage control. In the 3-phase buck boost rectifier a constant current through the buck boost inductor is needed to provide a unity power factor. But the pulse load in combination with the high dynamic voltage control would result in periodic peak currents at the converter input/mains and therefore a unity power factor at the input of the converter can not be guaranteed and the mains current would be distorted. Therefore, a new control for pulse load applications has to be implemented which achieves a unity power factor and an accurate regulation of the output voltage. First, in the paper the structure/operation principle of a standard buck boost converter is described and the problems resulting from the pulse load are discussed. Thereafter, a new control is derived which avoids the mentioned problems. Finally, the paper is concluded with measurement results for the input currents and the DC voltage during pulse operation.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/bortis_IEEETrans_25kWPulseLoad_02.pdf

25kW 3-Phase Unity Power Factor Buck Boost Rectifier with Wide Input and Output Range for Pulse Load Applications

The multi-cell converter approach allows to break the performance barriers of conventional systems by leveraging the advantages of using multiple interleaved low voltage and/or low current converter cells. In this digest, a fourth dimension of interleaving is proposed which considers the time dependent degrees of freedom in the control of the entire multi-cell converter system. This new control concept is based on the possibility to decouple the operation of the series connected input stages from the parallel connected output stages by using the energy storage capability of the DC-link capacitors. This digest shows how the 4D-interleaving concept improves the system performance such as the efficiency which will be demonstrated with measurement results on a hardware prototype system in the final paper.

4D-Interleaving of Isolated ISOP Multi-Cell Converter Systems for Single Phase AC/DC Conversion

This paper introduces the Interactive Power Electronics Seminar - iPES - a new software package for teaching of fundamentals of power electronic circuits and systems iPES is constituted by HTML text with Java applets for interactive animation, circuit design and simulation and visualization of electromagnetic fields and thermal issues in power electronics It does comprise an easy-to-use self-explaining graphical user interface The software does need Just a standard web-browser, ie no installations are required iFES can be accessed Via the World Wide Web or from a CD-ROM in a stand-alone PC by students and professionals Due to the underlying software technology IPES IS very flexible and could be used for on-line learning and could easily be integrated into an e-learning platform 
The aim of this paper is to give an introduction to the iPES-project and to show the different areas covered The e-learning software is available at no costs at www mesethzch in English, German, Japanese, Korean, Chinese and Spanish The project is still under development and the web page is updated m about 4 weeks intervals

/pdf/a-novel-interactive-power-electronics-seminar-ipes-developed-1tp4pw9ioq.pdf

A Novel Interactive Power Electronics Seminar (iPES) Developed at the Swiss Federal Institute of Technology (ETH) Zurich

Bearingless pumps have been established in applications that demand high purity and reliability. To expand their temperature operation range, careful machine design needs to be critical. High operating temperatures generate mechanical stress upon the dissimilar materials of the motor, such as potting, copper, iron, etc., shortening their lifetime. To guarantee faultless operation, precise knowledge about internal operating temperatures is required. A bearingless motor capable of pumping the highest fluid temperature (250  $^{\circ }$ C) to our knowledge is presented. Thermal and hydraulic performance are experimentally verified.

Ultra-High Temperature (250 $^{\circ }$ C) Bearingless Permanent Magnet Pump for Aggressive Fluids

In this paper, analytical calculations of the switching frequency harmonics of PWM-controlled 3-phase voltage-source DC/AC power converters are presented. Detailed knowledge of the modulation-dependent spectra of such systems is highly valuable for the EMI filter design and the estimation of the high-frequency losses in the filter components and the load. The paper presents a formula for the calculation of the switching frequency harmonics which is simple and highly versatile. It can be applied to converters with arbitrary numbers of voltage levels N and in combination with a broad variety of modulation signals. All calculations are verified by means of simulations and show a high accuracy over a wide range of input parameters. Finally, an EMI filter design example demonstrates the practical application and benefits of the derived formula. The MATLAB code used for the calculations is provided at the end of the paper.

Johann W. Kolar

Papers

25kW 3-Phase Unity Power Factor Buck Boost Rectifier with Wide Input and Output Range for Pulse Load Applications

4D-Interleaving of Isolated ISOP Multi-Cell Converter Systems for Single Phase AC/DC Conversion

A Novel Interactive Power Electronics Seminar (iPES) Developed at the Swiss Federal Institute of Technology (ETH) Zurich

Ultra-High Temperature (250 $^{\circ }$ C) Bearingless Permanent Magnet Pump for Aggressive Fluids

Low-complexity analytical approximations of switching frequency harmonics of 3-phase N-level voltage-source PWM converters