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

Research Challenges and Future Perspectives of Solid-State Transformer Technology

This paper considers the weight optimization of an axial-flux machine (AFM) for airborne wind turbines (AWT). It employs combined electrical, thermal and structural (mechanical) analytical models, which allow a fast evaluation of machine performance. Therefore, instead of introducing cost functions, the complete machine design space can be considered. The machines are shown in a performance space from which a Pareto limit can be clearly identified, and an optimal machine chosen for any given application. Optimization results yield a maximum power-to-weight ratio of 6.4 kW/kg including structural (non-electrical) parts, at an efficiency of 95 % and rated speed of 3200 rpm, which is unparalleled by commercial machines, or those reported in literature. Analytical models are verified by FEM simulations, and a prototype of the optimal AFM is built in order to experimentally confirm the results.

Weight optimization of an axial-flux PM machine for airborne wind turbines

For three-phase a.c.-a.c. power conversion a conventional matrix converter (CMC) or a d.c. side connection of a current DC link rectifier and a voltage d.c. link inverter comprising no energy storage components in the d.c. link could be employed. The combination of d.c. link converters does show a lower number of turn-off power semiconductors and, therefore, has been denoted as Sparse Matrix Converter (SMC) or Very Sparse Matrix Converter (VSMC). A limitation of the phase displacement of the current and voltage fundamentals at the input and at the output to ± π/6 does allow a further reduction of the system complexity, accordingly the respective topology has been introduced in the literature as Ultra Sparse Matrix Converter (USMC).In this paper a novel concept for the analytical calculation of the current stresses on the power semiconductors of the Sparse Matrix Converter Topologies (SMC, VSMC, and USMC) is proposed. As a comparison to a digital simulation shows, the analytical results do show a v...

Analytically Closed Calculation of the Conduction Losses of Three-Phase AC-AC Sparse Matrix Converters

This paper investigates the operation of the Dual Three-Phase Active Bridge (D3AB) converter topology as a multi-port converter, by taking the three-phase ac port and dc port on the primary side (ac 1 and dc 1 ) and the galvanically isolated three-phase ac port and dc port on the secondary side (ac 2 and dc 2 ) simultaneously into account. The basic working principle of the D3AB topology under multi-port operation and a strategy to achieve independent power transfer between the four ports are described. It is found that the realization of a power transfer between ac 1 and ac 2 , which can be operated with different line voltages and line frequencies, is particularly challenging, as compared to dc 1 –dc 2 operation. Therefore, this mode of operation is further analyzed and suitable modulation schemes are developed to achieve sinusoidal ac currents, constant dc-link voltages, and reduced low-frequency power pulsations between the ac ports. The derived analytical results are verified by means of circuit simulations and experiments, for a primary-side ac rms phase voltage of 115 V and line frequency of 50 Hz, a secondary-side ac rms phase voltage of 57.5 V and line frequency of 77 Hz, and an output power of 675 W.

Quad-Port AC–DC–DC–AC Operation of Isolated Dual Three-Phase Active Bridge Converter

Techniques have been presented in the literature for canceling stray capacitances for inductors in single-phase power filters. With the same aim, the flexibility of three-phase networks is here explored. A thorough theoretical analysis is presented, where pros and cons of parasitic cancellation networks are highlighted and improvements are proposed. A systematic mathematical procedure to evaluate impedances for different noise modes in three-phase circuits is presented. The influence of parasitic effects is accessed and asymmetrical capacitance cancellation is proposed, facilitating applications in switched power circuits. Experimental results are presented, which prove the feasibility of the presented techniques.

Johann W. Kolar

Papers

Research Challenges and Future Perspectives of Solid-State Transformer Technology

Weight optimization of an axial-flux PM machine for airborne wind turbines

Analytically Closed Calculation of the Conduction Losses of Three-Phase AC-AC Sparse Matrix Converters

Quad-Port AC–DC–DC–AC Operation of Isolated Dual Three-Phase Active Bridge Converter

Extending Winding Capacitance Cancellation to Three-Phase EMC Input Filter Networks