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.

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Recent Advances and Industrial Applications of Multilevel Converters

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

Three-Phase Unity Power Factor Mains Interfaces of High Power EV Battery Charging Systems

An extension of the partial element equivalent circuit (PEEC) method for magnetic materials modeling in the frequency domain applied on toroidal magnetic inductors with rectangular cross section is presented in this paper. The extension is performed by coupling the PEEC method and the boundary element method (BEM). The influence of magnetic material is modeled by distributions of “fictitious magnetic currents and charges” existing on the surface of a magnetic body. To verify the developed 3-D PEEC model, calculated and measured impedances are compared for two winding arrangements employing a ferrite T38 core. A good agreement between the PEEC simulation and measurements is presented up to the first resonant frequency. The described PEEC modeling approach enables 3-D electromagnetic simulations with much less computational effort than given for existing finite element method (FEM) simulators.

An extension of PEEC method for magnetic materials modeling in frequency domain

Three-Phase PFC Rectifier and AC-AC Converter Systems - PART 2

Our world is increasingly powered by electricity, which is largely converted to or from mechanical energy using electric motors. Several applications have driven the miniaturization of these machines, resulting in high rotational speeds. Although speeds of several hundred thousand revolutions per minute have been used industrially, we report the realization of an electrical motor reaching 40 million rpm to explore the underlying physical boundaries. Millimeter-scale steel spheres, which are levitated and accelerated by magnetic fields inside a vacuum, are used as a rotor. Circumferential speeds exceeding 1000 m/s and centrifugal accelerations of more than 4 × 108 times gravity were reached. The results open up new research possibilities, such as the testing of materials under extreme centrifugal load, and provide insights into the development of future electric drive systems.

Ultrafast rotation of magnetically levitated macroscopic steel spheres

The modeling and control of a three-phase, three-switch buck-type rectifier system with integrated boost output stage (VRX-4) is analyzed in this paper. A cascaded multi-loop control structure is presented that has the following features: constant output voltage for a wide input voltage range and step-wise changes of load; sinusoidal input currents in phase with the mains voltages that also remain sinusoidal in case of asymmetric mains conditions; and active damping of the input filter resonance. For the control design an equivalent DC-DC small-signal model of the converter is derived and verified by simulations and measurements. Based on this and the identification of the critical operating point the controllers for the inner DC current and outer voltage control loops are selected The stability of the closed loop system is discussed and the robust operation of the system is verified by measurements on a 5 kW prototype.

Johann W. Kolar

Papers

Three-Phase Unity Power Factor Mains Interfaces of High Power EV Battery Charging Systems

An extension of PEEC method for magnetic materials modeling in frequency domain

Three-Phase PFC Rectifier and AC-AC Converter Systems - PART 2

Ultrafast rotation of magnetically levitated macroscopic steel spheres

Control-oriented modeling and robust control of a three-phase buck+boost PWM rectifier (VRX-4)