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

In this paper we study a novel way of induction cooking. Traditionally, an alternating magnetic field is used to induce currents in a ferromagnetic pan to heat foods. We use non-ferromagnetic materials and optimize the design for high repulsive forces in order to levitate the pan while simultaneously heating it and its contents. Our approach is simulation-based to study the influence of different parameters and to perform multidimensional analyses for high force versus power or loss goals. Finally, an experimental prototype has been realized and successfully operated.

Optimizing repulsive lorentz forces for a levitating induction cooker

Converter topologies such as current-source rectifiers and inverters require switching devices with bipolar voltage blocking and unidirectional current conduction capability. Recently available dual-gate GaN monolithic bidirectional switches (MBDSs) can mimic such self-reverse-blocking (SRB) behavior if the MBDS’ two gates are controlled accordingly, but thus need twice the number of gate signals and gate drive circuits. Therefore, we propose cascode-diode control (i.e., without additional sensing or gate drive circuitry) of one MBDS gate using a cascode configuration with a low-voltage silicon Schottky diode. The resulting SRB-MBDS features quasi-ohmic conduction characteristic and single-gate control. We provide static and dynamic measurements of a discrete proof-of-concept realization (600-V, 190-m$\mathrm{\Omega }$ GaN MBDS; 40-V, 10-A silicon Schottky diode) that demonstrate the proposed SRB-MBDS’ feasibility.

Self-Reverse-Blocking Control of Dual-Gate Monolithic Bidirectional GaN Switch With Quasi-Ohmic on-State Characteristic

This paper investigates implications of Low-Frequency (LF) phase current distortions that emanate from a grid-connected three-phase PFC rectifier, which powers a single-phase load inverter via a common DC-link. The presented study reveals the computation of the grid-side distortions that result for LF operation of the load inverter and determines the limits of the allowable distortion currents imposed by relevant standards (IEC 61000-3-11 and IEC 61000-3-12 with regard to harmonic currents and flicker, respectively). In the course of a design example, a PFC rectifier with a rated power of 20 kW and a DC-link voltage of 700 V is examined and it is found that, in case of a strong grid with an inner impedance of 21 m Ω, full compliance with IEC 61000 is achieved with a DC-link capacitance of 27 mF. However, in case of a weak grid with an assumed inner impedance of 212 m Ω, a very high DC-link capacitance exceeding 50 mF would be required. In this case, the presented design procedure is rather used to identify the frequency-dependent power limitation characteristic that enables the implementation of deratings in critical frequency ranges.

Analysis of Low Frequency Grid Current Harmonics Caused by Load Power Pulsation in a 3-Phase PFC Rectifier

In this paper, total performance of two 20 kVA UPS realizations based on different design processes are compared in terms of losses and volumes. One of the design process employs a multi-objective optimization approach and Pareto analysis for selecting optimal design parameters. The other design process employs traditional industrial design approach. Employing the multi-objective optimization approach and Pareto analysis in the design process enables comparison and selection of suitable combinations of power semiconductor device for achieving minimum semiconductor losses. Thus, not only lower semiconductor losses but also lower heat sink volumes are achieved. In addition, it also enables selection of suitable magnetic material and design parameters, switching frequencies and relative current ripple, for reducing losses and volumes of inductors. As a result, the total volume of realized system based on the optimized design is 47% less than the other realization. On the other hand, costs are considered as one of the most important performance index in the industrial application. Challenges for including systematic costs analysis into the design process are also discussed.

Benefits and challenges of design process that employs a multi-objective optimization approach for industrial applications

The design of EMI-filters for converter systems is usually based on measurements with a prototype in the final stages of the design process. Predicting the conducted electromagnetic (EM) noise spectrum of a converter by simulation in an early stage has the potential to save time/cost and to investigate different noise reduction methods, which could e.g. influence the layout or the design of the control IC. Therefore, the main sources of conducted differential mode (DM) and common mode (CM) noise of electronic ballasts are identified in this paper. For each source, the noise spectrum is calculated and a noise propagation model is presented. There, also the influence of the LISN and the test receiver is included. Based on the presented models noise spectrums are calculated and validated by measurements.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/EMI-Noise.pdf

Johann W. Kolar

Papers

Optimizing repulsive lorentz forces for a levitating induction cooker

Self-Reverse-Blocking Control of Dual-Gate Monolithic Bidirectional GaN Switch With Quasi-Ohmic on-State Characteristic

Analysis of Low Frequency Grid Current Harmonics Caused by Load Power Pulsation in a 3-Phase PFC Rectifier

Benefits and challenges of design process that employs a multi-objective optimization approach for industrial applications

EMI noise prediction for electronic ballasts