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

For a 3-phase pulse width modulated high-bandwidth AC voltage source, this paper presents a series resonant DC-DC converter (SRC) with a high-frequency transformer operated by only two half-bridges interconnecting a 3-phase 3-level rectifier and 3-phase plus neutral conductor 3-level inverter stage. On the primary side, one terminal of the transformer is connected through the resonant capacitor and inductor to one bridge-leg output and the other terminal is connected to the DC-link midpoint. On the secondary side, both terminals directly connect to the second bridge-leg output and the DC-link midpoint. With the proposed SRC, the galvanic isolation and the balancing of the capacitor voltages of the inverter-side split DC-link can be achieved also for an unequal loading of the DC-link capacitors. The AC source needs to supply not only passive symmetrical 3-phase loads, but also passive or active single-phase, 2-phase, DC and asymmetrical 3-phase loads. Hence, the unequal loading of the DC-link capacitors can be generated, for example, in case a DC load is connected to the 4-wire inverter stage. The operation principle of the SRC is described in detail for an unequal loading of the DC-link capacitors. Moreover, design guidelines for the suggested SRC are derived and finally the theoretical analysis is successfully verified by measurements conducted on a 1 kW proof-of-concept SRC prototype.

Integrated isolation and voltage balancing link of 3-phase 3-level PWM rectifier and inverter systems

In the energy distribution grid of electric vehicles (EVs), multiple different voltage potentials need to be interconnected, to allow arbitrary power flow between the various energy sources and the different electrical loads. However, between the different potentials, galvanic isolation is absolutely necessary, either due to safety reasons and/or due to different grounding schemes. This paper presents an isolated three-port DC/DC converter topology, which, in combination with an upstream PFC rectifier, can be used as combined EV charger for interconnecting the single-phase AC mains, the high-voltage (HV) battery and the low-voltage (LV) bus in EVs. The proposed topology comprises two synergetically controlled and magnetically coupled converter parts, namely, a series-resonant converter between the PFC-sided DC-link capacitor and the HV battery, as well as a phase-shifted full-bridge circuit equivalent in the LV port, and is mainly characterized by simplicity in terms of control and circuit complexity. For this converter, a simple soft switching modulation scheme is proposed and comprehensively analyzed, in consideration of all parasitic components of a real converter implementation. Based on this analysis, the design of a 3.6 kW, 500 V/500 V/15 V prototype is discussed, striving for the highest possible power density and as low as possible manufacturing costs, by using PCB-integrated windings for all magnetic components. The hardware demonstrator achieves a measured full-load efficiency in charge mode of 96.5% for nominal operating conditions and a power density of 16.4  kWL−1.

Three-Port Series-Resonant DC/DC Converter for Automotive Charging Applications

In this paper the parallel connection of two three phase buck-type unity power factor rectifier systems is investigated experimentally for a 10 kW DSP-controlled prototype. There, a space vector modulation scheme is employed which shows all advantages of interleaved operation of the two systems. Three control schemes for active DC-side current balancing are described. The control schemes do differ concerning their control action and concerning additional switching losses. All control structures discussed in this paper are based on employing an additional free-wheeling states which do allow influence of the rate of change of the DC-side currents and can therefore be used for DC-side current balancing.

Experimental evaluation of space vector oriented active DC-side current balancing of two parallel connected three-phase three-switch buck-type unity power factor rectifier systems

The invention relates to a method for operating a converter circuit. To this end, the converter circuit comprises a converter unit (1) with a multitude of controllable power semiconductor switches and an energy store circuit (2) formed by two series-connected capacitors. The controllable power semiconductor switches are controlled by means of a control signal (S) formed from a hysteresis signal vector (x) and the hysteresis signal vector (x) is formed from a differential phase connection current vector (?ifi,i) by means of a hysteresis controller (6), and the differential phase connection current vector (?ifi,i) is formed by subtracting a phase connection current vector (ifi,i) from a reference phase connection current vector (ifi,i,ref), and the reference phase connection current vector (ifi,i,ref) is formed from a differential output value (Pdiff), a differential reactive power value (Qdiff) and of a phase flow vector (?g,as). In order to keep the switching frequency of the controllable power semiconductor switches as constant as possible, a current correction value (io) is additionally subtracted for forming the differential phase connection current vector (?ifi,i), the current correction value (io) being formed by integrating a phase connection voltage mean value (Uinv,A), and the phase connection voltage mean value (Uinv,A) is formed by determining the arithmetic mean of the phase connection voltages (Uinv,iM) with a reference point of the connection point (M) of the capacitors of the energy store circuit (2). The invention also relates to a device with which the method can be carried out in a particularly simple manner.

Method for operating a converter circuit and device for carrying out the method

Ein Verfahren umfasst das Wandeln von Leistung durch einen Leistungswandler, der mehrere Wandlerzellen und wenigstens eine Filterzelle aufweist, das Erhalten einer Zelleneingangsleistung an einem Zelleneingang und Bereitstellen einer Zellenausgangsleistung an einem Zellenausgang wenigstens einer der mehreren Wandlerzellen, und das Betreiben der Filterzelle in einem von einem Eingangsleistungsbetrieb, in dem die Filterzelle eine Eingangsleistung erhalt, und einem Ausgangsleistungsbetrieb, in dem die Filterzelle eine Ausgangsleistung bereitstellt.

Johann W. Kolar

Papers

Integrated isolation and voltage balancing link of 3-phase 3-level PWM rectifier and inverter systems

Three-Port Series-Resonant DC/DC Converter for Automotive Charging Applications

Experimental evaluation of space vector oriented active DC-side current balancing of two parallel connected three-phase three-switch buck-type unity power factor rectifier systems

Method for operating a converter circuit and device for carrying out the method

Multizellen-Leistungswandlungsverfahren und Multizellen-Leistungswandler