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

Dual Active Bridge (DAB) converters are nowadays used in applications such as automotive and general energy storage interfaces, where efficient and compact isolated bidirectional DC/DC converters are required. The heart of this converter is a transformer which, in some designs, may include the required inductance to shape the current and control the energy transfer. This paper shows that for these designs, tape wound cores, usually made of amorphous or nanocrystalline materials, are not the best core option due to leakage flux which is orthogonal to the lamination layers. This flux increases losses in these types of cores. Solutions are proposed to overcome this significant drawback. Analysis developed in this paper is validated by experimental results, which show that core losses due to orthogonal flux in a tape wound core transformer can be reduced more than 6 times if an adapted leakage layer is used instead of a regular one.

Integration of Leakage Inductance in Tape Wound Core Transformers for Dual Active Bridge Converters

∗Power semiconductors can be modeled as a thermal network of resistors and capacitors. The thermal boundary condition of such a model is typically defined as the heat sink surface temperature, which is assumed to be constant. In reality, the heat sink surface temperature underneath the power module is not exactly known. In this paper we show how to set up a thermal model of the heat sink in form of a RC thermal equivalent network that can be directly embedded in any circuit simulator. The proposed thermal heat sink model takes into account convection cooling, thermal hotspots on the heat sink base plate, thermal time constants of the heat sink, and thermal coupling between different power modules mounted onto the heat sink. Experimental results are given and show high accuracy of the heat sink model with temperature errors below 10%.

/pdf/a-thermal-model-of-a-forced-cooled-heat-sink-for-transient-5ddo6g9681.pdf

A Thermal Model of a Forced-Cooled Heat Sink for Transient Temperature Calculations Employing a Circuit Simulator

For a Three-Level Three-phase T-type (3LTTC) rectifier and inverter of a high efficiency Uninterruptible Power Supply (UPS) with an output power of 20 kVA, most suitable semiconductor components are selected. For this purpose, this paper details conduction and switching loss models of T-type rectifiers and inverters, compares the total semiconductor losses achieved for RB-IGBTs and for different types of conventional IGBTs, and evaluates the improvements achieved if the Si rectifier diodes are replaced by SiC Schottky Barrier Diodes (SiC SBDs). The switching loss model is parameterized with measured switching losses. According to the results of this comparison, the rectifier preferably employs RB-IGBTs to realize the bi-directional switch and SiC SBDs for the rectifier diodes; switching frequencies up to 32.5 kHz are feasible for total semiconductor losses of the rectifier of 250W. For the inverter, a realization of the bi-directional switch using an anti-series connection of conventional IGBT/SiC SBD modules is found to be most suitable and facilitates a switching frequency of 19.7 kHz for maximum allowed losses of 250 W.

Comparative evaluation of T-type topologies comprising standard and reverse-blocking IGBTs

For various electrical interconnect and EMC problems, the partial element equivalent circuit (PEEC) method has proven to be a valid and fast solution method of the electrical field integral equation in the time as well as the frequency domain. Therefore, PEEC has become a multipurpose full-wave method, especially suited for the solution of combined circuit and EM problems, as found, for instance, on printed circuit board layouts, power electronics devices or EMC filters. Recent research introduced various extensions to the basic PEEC approach, for example a non-orthogonal cell geometry formulation. This paper presents a fast, flexible and accurate computational method for determining the matrix entries of partial inductances and the coefficients of potential for general non-orthogonal PEEC cell geometries. The presented computation method utilizes analytical filament formulas to reduce the integration order and therefore to reduce computation time. The validity, accuracy, and speed of the proposed method is compared with a standard integration routine on example cell geometries where the numeric results of the new method show improved accuracy, coming along with reduced computation time.

/pdf/efficient-calculation-of-non-orthogonal-partial-elements-for-26p6k2v751.pdf

Efficient Calculation of Non-Orthogonal Partial Elements for the PEEC Method

An increasing number of telecom, data server and aircraft power supply applications require high power, highly efficient, compact, sinusoidal input current rectifiers The design and experimental performance of an 85 kW/liter (139 W/in3), 3-phase PWM rectifier with a power output of 10 kW is presented The high power density is achieved by increasing the switching frequency up to 400 kHz, which results in smaller EMI filters and boost inductors, while still maintaining a high efficiency over 95% To minimize the switching losses, a combination of a CoolMOS and SiC diode are used in a custom power module The module together with an optimized forced air cooled heat sink, optimized EMI filter, and a fully digital controller are used to obtain the high power density of the rectifier

/pdf/ultra-compact-three-phase-pwm-rectifier-3xhlauiqp9.pdf

Johann W. Kolar

Papers

Integration of Leakage Inductance in Tape Wound Core Transformers for Dual Active Bridge Converters

A Thermal Model of a Forced-Cooled Heat Sink for Transient Temperature Calculations Employing a Circuit Simulator

Comparative evaluation of T-type topologies comprising standard and reverse-blocking IGBTs

Efficient Calculation of Non-Orthogonal Partial Elements for the PEEC Method

Ultra Compact Three-phase PWM Rectifier