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 power modulators for pulses in the microsecond range, transformers are often used for generating high output voltages. With standard topologies, the transformer is usually only excited in a unipolar direction, i.e., the flux density B swings between zero and a value close to the saturation flux density. By applying a reset circuit, the flux density B in the transformer is set to a value close to the negative saturation flux density before the pulse, so that the flux density could swing between the negative and positive saturation values during the pulse. This allows one to halve the core area and reduce the core volume/weight as well as the losses. In this paper, the operating modes of three different reset circuit topologies (the standard and a new advanced passive as well as an active one) and the corresponding waveforms are explained. Furthermore, the three topologies are compared with respect to the losses/complexity based on a design for a solid-state modulator with 20-MW output power and 200-kV output voltage..

Reset Circuits With Energy Recovery for Solid-State Modulators

In this work a compact-model-based inductor design procedure is presented. The losses, temperatures, and the total cost of ownership (TCO) of an inductor are expressed analytically. All geometric dependencies are summarized in a set of parameters which are calculated using finite element analysis (FEA). Therefore the model does not depend on the actual inductor geometry, instead it only relies on a generalized set of parameters which contain all geometric information. Different inductor geometries only result in different values of parameters. The dynamic thermal model is verified using time dependent FEA, the high frequency winding loss model is verified by measurements. The inductor model is then used to study the effect of changes in inductor geometry on the performance of the device. It is shown that for applications requiring high peak but low average load substantial cost reductions are achieved if the inductor's geometry is optimized and the right inductor topology is selected.

Comparative Analysis of Inductor Concepts for High Peak Load Low Duty Cycle Operation

Solid-State Transformers (SST) Concepts, Challenges and Opportunities

The productivity of AC electric arc smelters widely used in the nonferrous metals industry is related to the arc voltage. Attempts to improve productivity with longer arcs and higher arc voltages give rise to power fluctuations which cause voltage flicker and frequent arc reignition failures. The furnace power is commonly regulated by moving the electrode rods to adjust the arc length. A 100 MW AC arc furnace power supply equipped with semiconductor switched regulation windings which greatly enhance furnace power control bandwidth is presented, along with suitable winding arrangements, semiconductor topologies, harmonic filters and commutation methods. This system was simulated together with a Cassie-Mayr dynamic arc model. The simulation model as well as the four-step commutation sequence has been experimentally verified by building and testing a single phase 230 V, 2 kW PWM modulated tap-changer. The simulations and experiments demonstrate that power-electronic transformer tap-changers with the ratings necessary for AC arc furnace power supplies are within reach of current semiconductor technology. They are significantly more effective at AC arc furnace power regulation in terms of device rated power than controlled series reactor approaches.

Power-Electronic Transformer Tap-Changer for Increased AC Arc Furnace Productivity

In many pulsed-power applications, the flatness of the output pulse is an important characteristic to enable proper system operation, whereas a pulse flatness within less than a few percent has to be achieved. In power modulators based on capacitor discharge, this voltage droop is mainly defined by the input capacitance. In order to overcome this problem, in power modulator systems, compensation circuits are added, whereby in spite of a smaller storage capacitor, a flat pulse top is achieved. Depending on the pulse duration, different approaches for voltage droop compensation exist. For short pulse durations, in the range of several microseconds, only passive solutions or bouncer circuits are applicable. In this paper, the design and optimization of a two-winding inductor bouncer circuit are presented in order to achieve an output voltage droop of less than 1%. Due to the realized galvanic isolation, a new degree of freedom is obtained, which allows an adaptation of the bouncer circuit's voltage and current ratings to standard semiconductor switches. With an optimal design of the two-winding inductor bouncer circuit for the existing system, the volume of the input capacitor is reduced by a factor of 10.5, and the stored energy is decreased by a factor of 24 compared to a system without a bouncer circuit.

Johann W. Kolar

Papers

Reset Circuits With Energy Recovery for Solid-State Modulators

Comparative Analysis of Inductor Concepts for High Peak Load Low Duty Cycle Operation

Solid-State Transformers (SST) Concepts, Challenges and Opportunities

Power-Electronic Transformer Tap-Changer for Increased AC Arc Furnace Productivity

Optimal Design of a Two-Winding Inductor Bouncer Circuit