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

This paper details weight and efficiency analysis of a bidirectional ±270V dc to 3-phase 115V ac power electronic interface as part of an integrated modular power electronics cabinet, which supplies various loads, such as motors and ac buses from a HVDC bus in more electric aircraft. Through a case study the analysis shows that a significant reduction of filter component weight is achieved with a 3-level instead of a 2-level topology. The interactions and trade offs between the power electronic switched circuits and the EMI filter are analyzed and quantified. The potential benefits through the use of SiC-MOSFET's instead of Si-IGBTs and the implications for the circuit topologies are detailed. Recommendations for the choice of the optimal switched circuit topology, dependent on the importances of efficiency, weight, and reliability, are proposed. Furthermore, recommendations for the focus of future research enabling the competitiveness of the MEA concept is given.

Weight and efficiency analysis of switched circuit topologies for modular power electronics in MEA

The non-ideal behavior of semiconductor devices used in power electronic circuits exciting a transformer can cause DC voltage components applied to the transformer terminals. This DC voltage in turn generates a DC current and/or DC flux density component only limited by the parasitic resistance of the windings and semiconductors. The biased flux density operation deteriorates the performance of the converter, since the core can be driven into saturation, generating higher currents and hence higher temperatures in the circuit. In order to overcome this problem, the previously reported “Magnetic Ear”, a non-invasive flux density transducer concept, is used in this paper. The design, placement and all implementation issues for this flux density transducer are described. For verifying the theoretical considerations, the transducer is used to perform a closed loop control over the DC component of the flux density in the 166kW/20kHz transformer, therefore ensuring its unbiased magnetic flux density operation.

Application of the magnetic ear for flux balancing of a 160kW/20kHz DC-DC converter transformer

The Input Series Output Parallel (ISOP) multi-cell converter approach allows breaking the performance barriers of conventional single-cell telecom rectifier systems by leveraging the advantages of using multiple interleaved low-voltage and/or low-current converter cells. The ISOP interconnection in the DC/DC converter part of the cells, however, requires the employment of some kind of isolation in each cell, which is typically provided by transformers. An analysis of the losses and of the volume of the entire multi-cell system reveals that these transformers contribute a major part to the system losses and are responsible for a significant share of the total volume. However, as the transformers are mainly required for providing galvanic isolation in the ISOP structure and not for voltage conversion, series capacitors represent an alternative to decouple the series connected input terminals of the cells from the parallel connected output terminals. Compared to conventional solutions with transformers, the resulting capacitive power transfer ISOP multi-cell DC/DC converter (CPT-ISOP-MCC) system features lower losses and a smaller volume. In this paper, the benefits as well as the limitations in the design and operation of CPT-ISOP-MCC systems are analyzed in detail. In order to comprehensively evaluate the CPT against the magnetically isolated concept, i.e. inductive power transfer (IPT) converter topology, a multi-objective optimization is performed with respect to the achievable efficiency and power density for both types of converters. Based on the optimization result, a prototype of a CPT GaN DC/DC converter is realized and compared to its IPT GaN DC/DC converter counterpart, along with measurement results. Furthermore, a complete single-phase 3.3kWAC/DC converter system with a high power density of ρ = 3.92kW/dm3 and an efficiency of η = 97% is presented, incorporating the CPT-DC/DC converter stages in ISOP topology.

Analysis of capacitive power transfer GaN ISOP multi-cell DC/DC converter systems for single-phase telecom power supply modules

A switching device for switching a current between a first terminal (1) and a second terminal (2) comprises a cascode circuit having a series connection of a first semiconductor switch (M) and a second semiconductor switch (J), wherein the two semiconductor switches (M, J) are connected to each other by a common point (13), and the first semiconductor switch (M) is controlled by way of a first control input in accordance with a voltage between the first control input and the first terminal (1), and the second semiconductor switch (J) is controlled by way of a second control input (4) in accordance with a voltage between the second control input (4) and the common point (13). To this end, a control circuit having a specifiable capacitance (C) is connected between the second terminal (2) and at least one of the control input.

Switching device with a cascode circuit

The paper summarizes a step by step Partial Element Equivalent Circuit (PEEC) modeling approach for Electromagnetic Interference (EMI) filter components (e.g. foil capacitors, common mode and differential mode inductors) and PCB tracks, to design complete EMI input filters with an optimal selection and placement of the individual components. The presence of magnetic cores is modeled with the proposed PEEC-Boundary Integral Coupled Method (PEEC-BIM) by means of fictitious magnetic surface currents, using the core geometry and permeability as inputs. The developed PEEC based models are verified by transfer function measurements of several single-phase single/two-stage filter circuits. The resulting PEEC simulation time is determined by the time required to perform the surface mesh of the magnetic volume and is in the order of several minutes. The good results of the presented PEEC modeling approach enable a fast virtual design of EMI filters and help to accelerate the design process of power converter systems.

Johann W. Kolar

Papers

Weight and efficiency analysis of switched circuit topologies for modular power electronics in MEA

Application of the magnetic ear for flux balancing of a 160kW/20kHz DC-DC converter transformer

Analysis of capacitive power transfer GaN ISOP multi-cell DC/DC converter systems for single-phase telecom power supply modules

Switching device with a cascode circuit

PEEC-based virtual design of EMI input filters