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

Calculation of the Passive and Active Component Stress of Three-Phase PWM Converter Systems with High Pulse Rate

This paper presents a study and practical implementation of an active filter employing a high-frequency (HF) power amplifier and passive-filter components to be connected to the ac power lines in order to mitigate common-mode conducted emissions of three-phase pulsewidth modulation converter systems. The filter topology is chosen from different possibilities listed in a literature survey and studied regarding practical implementation issues, where requirements for an HF power amplifier to be applied in active filtering are derived. Special attention is put on the stability analysis where the challenges for the feedback are discussed, and a simple feedback structure is proposed. Other feedback concepts are analyzed, and limitations posed by stability requirements are presented. A prototype is designed and built, from which mathematical and experimental results are obtained demonstrating the potential and limitations of such a system.

Implementation of a Transformerless Common-Mode Active Filter for Offline Converter Systems

/pdf/highly-compact-isolated-gate-driver-with-ultrafast-3v19j5jhec.pdf

Highly Compact Isolated Gate Driver With Ultrafast Overcurrent Protection for 10 kV SiC MOSFETs

Although multilevel inverters present numerous advantages such as high quality waveform, low switching losses, high voltage capability and low electromagnetic compatibility concerns, some drawbacks are evident. They require a higher number of semiconductors and either multiple isolated dc sources or a bank of series connected capacitors. Consequently, the control complexity increases considerably, since more switching devices normally result in a higher number of possible combinations and the balance of the capacitors has to be guaranteed. But on the other hand, multilevel inverters create an extra degree of freedom due to existing redundant voltage vectors, which produce the same output phase voltage level but with diverse effect on the dc-link and floating capacitors. Among the existing control techniques the virtual-flux direct power control (VF-DPC) has showed to be very suitable for grid connected systems since it controls the active and reactive powers directly without any internal current control loop or PWM modulator. However, in order to adapt the VF-DPC for multilevel systems, specifically for the recently proposed five-level Active Neutral-Point Clamped converter, additional features must be included and/or modified in the inner main control loop. In order to allow the controller to select a higher number of available voltage vectors, the active and reactive power hysteresis strategies are modified. Additionally, a method to balance the dc-link and floating capacitor voltages by applying available redundant states is implemented, based on the actual condition of the voltage across the lower dc-link and floating capacitors, as well output phase currents direction. The proposed five-level VF-DPC has been implemented using a 6 kW five-level prototype and has shown good static and dynamic performance.

Five-level virtual-flux direct power control for the active neutral-point clamped multilevel inverter

As this paper shows, the magnetic coupling of the inductances of two hysteresis-controlled single-phase AC-to-DC boost power converters connected in parallel leads in connection with a delayed switching of the power transistors to a self-adjusting staggered switching of the partial systems. Thereby, a significant reduction of the ripple of the resulting mains current as compared to the uncoupled case is obtained. Based on the analytical description of the current shapes within a pulse period the dependency on the circuit parameters of the occurring phase displacement of the switching functions of the partial systems is calculated. Furthermore, the effect of an unsymmetry of the power converters on the system behavior is analyzed and the automatic adjustment of the phase shift within a mains period is investigated by digital simulation. The theoretical considerations are verified by measurements on a laboratory model. Finally, the possibility of a substitution of the magnetic coupling of the input inductances of the partial systems by a coupling of the current controls of the power converters is discussed. >

Johann W. Kolar

Papers

Calculation of the Passive and Active Component Stress of Three-Phase PWM Converter Systems with High Pulse Rate

Implementation of a Transformerless Common-Mode Active Filter for Offline Converter Systems

Highly Compact Isolated Gate Driver With Ultrafast Overcurrent Protection for 10 kV SiC MOSFETs

Five-level virtual-flux direct power control for the active neutral-point clamped multilevel inverter

Self-adjusting input current ripple cancellation of coupled parallel connected hysteresis-controlled boost power factor correctors