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

This paper presents a novel DC-AC converter for applications in the area of distributed energy generation systems, e.g., solar power systems, fuel-cell power systems in combination with supercapacitor or battery energy storage. The proposed converter is realized using an isolated multicell topology where the total AC output of the system is formed by series connection of several full-bridge converter stages. The DC links of the full bridges are supplied by individual DC-DC isolation stages which are arranged in parallel concerning the dc input of the. total system. Therefore, all switching cells of the proposed converter can be equipped with modern low-voltage high-current power MOSFETs, which results in an improved efficiency as compared to conventional isolated DC-AC converters. Furthermore, the cells are operated in an interleaved pulsewidth-modulation mode which, in connection with the low voltage level of each cell, significantly reduces the filtering effort on the AC output of the overall system. The paper describes the operating principle, analyzes the fundamental relationships which are relevant for component selection, and presents a specific circuit design. Finally, measurements taken from a 2-kW laboratory model are presented.

http://www.initkms.ru/umk/etf/d/A_novel_multi-cell_DA-AC_converter_for...(Ertl_H._etc.).pdf

A novel multicell DC-AC converter for applications in renewable energy systems

This paper proposes a novel approach to adapt a conventional direct power control (DPC) for high-power applications, where a third-order LCL filter is frequently required. The LCL filter can cause a strong resonance and requires additional effort for system control. The application of a DPC for the control of a three-phase voltage source inverter that is connected to the grid through an filter has not yet been considered. The addition of an active damping strategy, together with a harmonic rejection control loop, to the conventional DPC is proposed and analyzed in this paper. The steady-state, as well as the dynamic performance of the proposed system, is verified with simulation results and experimental measurements.

A Modified Direct Power Control Strategy Allowing the Connection of Three-Phase Inverters to the Grid Through $LCL$ Filters

The design of a 1 MW, 20 kHz, isolated, bidirectional 12kV to 1.2kV DC-DC converter for renewable energy applications is presented. The main topics addressed are: High-Voltage (HV) side switch, topology & modulation and Medium Frequency (MF) transformer. A study of the possible HV side switches, considering 4.5kV IGBTs is performed, fixing the requirements from the topology and modulation side in order to reach a highly efficient system. The studied topologies are the Dual Active Bridge (DAB) with triangular modulation and the Series Resonant Converter (SRC) with constant frequency operation. Both topologies are able to achieve Zero Current Switching (ZCS) in the HV side switches, reducing the switching losses in these devices, which contribute to a large share to the system losses. Efficiency curves are presented for different semiconductor technologies for the Low-Voltage (LV) side switch in order to study the trade-offs between the selected topologies. Three MF transformer concepts, namely core-type, shell-type and matrix transformer, are presented and compared in respect of winding arrangement, isolation mechanisms and thermal management. Power losses and volume are calculated in each case and used to compare the different transformer concepts.

1 Megawatt, 20 kHz, isolated, bidirectional 12kV to 1.2kV DC-DC converter for renewable energy applications

Inductive power transfer (IPT) is an attractive solution for the automated battery charging of public transport electric vehicles (EVs) with low maintenance requirements. This paper presents the design of a 50 kW/85 kHz contactless EV charger, with a focus on the IPT transmitter and receiver coils. The multi-objective magnetics optimization reveals the Pareto tradeoffs and performance limitations in terms of high efficiency, high power density, and low stray field for high-power IPT systems without moving mechanical parts. A full-scale hardware prototype is realized and experimentally investigated. The dc-dc conversion efficiency, including all the power electronics stages, is measured as 95.8% at 50 kW power transfer across an air gap of 160 mm (coil dimensions $410\times 760\times 60$ mm3). With 150 mm coil misalignment in the worst case direction, the dc-dc efficiency drops to 92%. The measurements of the magnetic stray field show compliance with ICNIRP 2010 at 800 mm distance from the IPT coil center.

Multi-Objective Optimization of 50 kW/85 kHz IPT System for Public Transport

This paper provides a comprehensive guideline for the design of a single-phase PFC targeting for minimal volume, as it is highly relevant for ultracompact integrated systems. It is shown, how different operation modes (continuous, boundary, and discontinuous conduction mode) may influence the design and consequently the achieved power density. Furthermore, the effect of interleaving of several boost stages is analyzed as a measure for compactness increase. Finally, the selection of the appropriate switching frequency in order to achieve an overall optimized system is discussed. In this way, the design of the crucial components is carried out, namely, the boost inductor, including a volume optimization through a thermal connection to the heat sink; the output capacitor considering the rms current stress; and the input filter, which is designed for compliance with high-frequency electromagnetic compatibility standards, taking into account the quasi-peak detection measurement of the test receiver equipment.

Johann W. Kolar

Papers

A novel multicell DC-AC converter for applications in renewable energy systems

A Modified Direct Power Control Strategy Allowing the Connection of Three-Phase Inverters to the Grid Through $LCL$ Filters

1 Megawatt, 20 kHz, isolated, bidirectional 12kV to 1.2kV DC-DC converter for renewable energy applications

Multi-Objective Optimization of 50 kW/85 kHz IPT System for Public Transport

Design Guidelines for Interleaved Single-Phase Boost PFC Circuits