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

Strings of photovoltaic panels have a significantly reduced power output when mismatch between the panels, such as partial shading, occurs since integrated diodes are then partly bypassing the shaded panels. With the implementation of DC-DC converters on panel level, the maximum available power can be extracted from each panel regardless of any shading. In this paper, different concepts of PV panel integrated DC-DC converters are presented, comparative evaluation is given and the converter design process is shown for the buck-boost converter which is identified as the best suited concept. Furthermore, the results of high precision efficiency measurements of an experimental prototype are presented and compared to a commercial MIC.

Classification and comparative evaluation of PV panel integrated DC-DC converter concepts

In this paper a simple analytical expression for the current stress on the DC link capacitor of a voltage DC link converter system, as caused by the load-side inverter is derived. There, a sinusoidal inverter output current and a constant value of the DC link voltage are assumed. The DC link capacitor current RMS value is determined by the modulation depth and by the amplitude and the phase angle of the inverter output current. Despite the neglection of the output current ripple the results of the analytical calculation match very well with a digital simulation even if the output current ripple is relatively high as given, e.g., for low-frequency IGBT inverter systems. Thus, the approximation can advantageously be used for designing the DC link capacitor of PWM converter systems.

Analytical calculation of the RMS current stress on the DC link capacitor of voltage DC link PWM converter systems

Electromagnetic compatibility (EMC) filters are typically included in offline power converters, controlling electromagnetic emissions, but adding volume to power electronic systems. During the last decades, one of the main objectives of the power electronics industry has been the increase of the power density. Thus, it is reasonable to analyze how filters affect power density values, imposing limits or ldquobarriersrdquo to it. The impact of the EMC filters on the overall volume of three-phase pulsewidth modulation (PWM) converters is studied here for converters in the range of 5-10 kW. An analytical procedure based on the volume minimization of the EMC filters is proposed to estimate the total filter volume as function of the converters' rated power and switching frequency. With this, the minimum volume for EMC filters that allow the converters to comply with EMC standards regarding conducted emissions can be estimated and volume limitations identified. A discussion about the limits of power density for the considered three-phase PWM converters for state-of-the-art power semiconductors is performed, and optimum switching frequencies are identified. An experimental verification is carried out, which validates the achieved results.

Impact of EMC Filters on the Power Density of Modern Three-Phase PWM Converters

This paper presents a novel switch-mode power amplifier based on a multicell multilevel circuit topology. The total output voltage of the system is formed by series connection of several switching cells having a low DC-link voltage. Therefore, the cells can be realized using modern low-voltage high-current power MOSFET devices and the DC link can easily be buffered by rechargeable batteries or "super" capacitors to achieve very high amplifier peak output power levels ("flying-battery" concept). The cells are operated in a phase-shifted interleaved pulsewidth-modulation mode, which, in connection with the low partial voltage of each cell, reduces the filtering effort at the output of the total amplifier to a large extent and, consequently, improves the dynamic system behavior. The paper describes the operating principle of the system, analyzes the fundamental relationships being relevant for the circuit design, and gives guidelines for the dimensioning of the control circuit. Furthermore, simulation results as well as results of measurements taken from a laboratory setup are presented.

Analysis of a multilevel multicell switch-mode power amplifier employing the "flying-battery" concept

In this paper, a closed-loop active IGBT gate drive providing highly dynamic di C /dt and dv CE /dt control is proposed By means of using only simple passive measurement circuits for the generation of the feedback signals and a single operational amplifier as PI-controller, high analog control bandwidth is achieved enabling the application even for switching times in the sub-microsecond range

Johann W. Kolar

Papers

Classification and comparative evaluation of PV panel integrated DC-DC converter concepts

Analytical calculation of the RMS current stress on the DC link capacitor of voltage DC link PWM converter systems

Impact of EMC Filters on the Power Density of Modern Three-Phase PWM Converters

Analysis of a multilevel multicell switch-mode power amplifier employing the "flying-battery" concept

Closed-loop IGBT gate drive featuring highly dynamic di/dt and dv/dt control