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 more and more pulsed power applications solid state modulators are applied. There, often IGBT modules must be connected in parallel due to their limited power handling capability. For balancing the currents in the IGBTs a control method adapting the gate signal of the single IGBTs has been presented in a previous paper. Besides the current balancing also the fall and rise times of the voltages/currents are crucial as they significantly influence the pulse shape and the modulator efficiency. For reducing the rise time of the pulse without increasing the maximal over-voltage of the IGBT a double-stage gate driver for parallel connected IGBTs is presented in this paper. In this gate driver also protection circuits for avoiding over-voltages as well as over-currents are included and an improved current balancing method is incorporated. Finally, measurement results revealing the dependency of the rise time/turn off losses on the design parameters of the gate drive are presented.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/05211849_01.pdf

Double-Stage Gate Drive Circuit for Parallel Connected IGBT Modules

In pulse modulators applying pulse transformers reset circuits are used to achieve optimal utilization of the core material, which results in lower costs, downsized pulse transformer/system volume and therefore in an improved pulse behavior due to the smaller parasitics. Because of its simplicity the most common method to reset the core is a dc reset circuit, where a dc current is used to premagnetize the core. However, the dc reset circuit - even with an optimal design - leads to significant losses in the freewheeling path. By applying an active reset method the losses due to the passive reset circuit can be significantly. So far, only the theoretical behavior of the active reset circuit has been examined. Therefore, the detailed design and measurement results are presented in this paper. Furthermore, a new control method for achieving symmetrical flux swings in the core are presented.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/05211837_01.pdf

Design and Control of an Active Reset Circuit for Pulse Transformers

A design procedure is proposed for the EMC filters to be included in a three-phase/-level PWM rectifier unit in order to fulfill EMC requirements related to conducted emissions. An analytical volumetric optimization is performed considering constraints given by electrical safety, power factor and damping of resonances. The procedure avoids the necessity of applying numerical optimization allowing the analytical calculation of the total filter volume as function of rated power and switching frequency. A discussion about the limits of power density for the rectifier employing modern power semiconductors is done and optimum switching frequency of 540 kHz is calculated for a forced air-cooled system. The experimental verification of the proposed procedure is presented through CE measurements in the designed system. Keywords―Input filter, Minimum volume filters, Threephase filter design, Ultra-Compact Rectifier.

/pdf/design-of-minimum-volume-emc-input-filters-for-an-ultra-3zaqxbio9t.pdf

Design Of Minimum Volume Emc Input Filters For An Ultra Compact Three-phase Pwm Rectifier

This paper describes a novel and compact design concept for contactless levitation and rotation of a wide annular rotor through the walls of a process chamber. In the proposed set-up, a homopolar magnetic bearing biased by permanent magnets is combined with a high-pole-number segment motor. The paper describes the functional principle of the motor focusing on the design and the behavior of the drive. An experimental system is presented along with a comprehensive set of measurement results verifying the theoretical considerations.

Novel Integrated Bearingless Hollow-Shaft Drive

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 modulators 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 µs, only passive solutions or bouncer circuits are applicable. In this paper the design and optimization of a two-winding inductor bouncer circuit is 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 adaption of the bouncer circuit's voltage and current rating 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 system without bouncer circuit.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/Two_Winding.pdf

Johann W. Kolar

Papers

Double-Stage Gate Drive Circuit for Parallel Connected IGBT Modules

Design and Control of an Active Reset Circuit for Pulse Transformers

Design Of Minimum Volume Emc Input Filters For An Ultra Compact Three-phase Pwm Rectifier

Novel Integrated Bearingless Hollow-Shaft Drive

Optimal design of a two-winding inductor bouncer circuit