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

The future trends in microprocessor supply current requirements represent a bottleneck for next generation high-performance microprocessors since the number of supply pins will constitute an increasingly larger fraction of the total number of package pins available. This leaves few pins available for signaling. On-chip power conversion is a means to overcome this limitation by increasing the input voltage - thereby reducing the input current - and performing the final power conversion on the chip itself. This paper details the design and implementation of on-chip switched capacitor converters in deep submicron technologies. High capacitance density deep trench capacitors with a low parasitic bottom plate capacitor ratio available in the technology facilitate high power density and efficiency in on-chip switched capacitor converter implementations. The measured performance of a 2 : 1 voltage conversion ratio on-chip switched capacitor converter implemented in 32nm SOI CMOS technology with 1.8V input voltage results in a power density of 4.6W/mm2 at 86% efficiency when operated at a switching frequency of 100MHz.

A 4.6W/mm 2 power density 86% efficiency on-chip switched capacitor DC-DC converter in 32 nm SOI CMOS

Frequency controlled Inductive Power Transfer (IPT) systems for Electric Vehicle (EV) battery charging applications often suffer from high power losses in partial-load, because the transmitter coil current is not significantly reduced at low output power. Therefore, in this paper a novel control method is presented that exhibits a substantially higher partial-load efficiency, while it also enables full control of the power semiconductor switching conditions. The power flow control is based on the dynamic regulation of the dc-link voltages on both sides of the resonant system with dc-dc-converters. Additionally, a tracking of the resonance with a current zero crossing detection circuit and a PLL makes the switched current an additional degree of freedom, that can be used, e.g., for the minimization of IGBT soft-switching losses due to stored-charge. All calculated results are supported by experimental measurements on an existing 5 kW/52mm air gap/210mm coil diameter prototype system with an efficiency of more than 96.5% at maximum power and above 96% down to 20% rated power.

Control method for Inductive Power Transfer with high partial-load efficiency and resonance tracking

A switching control strategy to enable Zero-Voltage-Switching (ZVS) over the entire input-voltage interval and the full power range of a single-stage Dual Active Bridge (DAB) AC/DC converter is proposed. The converter topology consists of a DAB DC/DC converter, receiving a rectified AC line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and inductor. Using conventional control strategies, the soft-switching boundary conditions are exceeded at the higher voltage conversion ratios of the AC input interval. Recently we presented a novel pulse-width-modulation strategy to fully eliminate these boundaries, using a half bridge — full bridge DAB configuration. In this papers the analysis is extended towards a full bridge — full bridge DAB setup, providing more flexibility to minimize the component RMS currents and allowing increased performance (in terms of efficiency and volume). Experimental results are given to validate the theoretical analysis and practical feasibility of the proposed strategy.

Switching control strategy for full ZVS soft-switching operation of a Dual Active Bridge AC/DC converter

New emerging micro gas turbine generator sets and turbocompressor systems push the speed limits of rotating machinery. To directly connect to these applications, ultra-high-speed electrical drive systems are needed. Therefore a 1 kW, 500000 rpm machine and the according power and control electronics are designed and built. This paper includes design considerations for the mechanical and electromagnetic machine design. Furthermore, a voltage source inverter with an additional dc-dc converter is described, and sensorless rotor position detection and digital control is used to drive the machine. Finally, the hardware and experimental results are presented.

An Ultra-High-Speed, 500000 rpm, 1 kW Electrical Drive System

A Sparse Matrix Converter (SMC) is a direct AC/AC converter that contains no large energy storage components. A 100 kHz, 1.5 kW SiC SMC is presented, which uses 1300 V, 4 A SiC JFET cascode devices. The SMC is operated from a 50 Hz, 230 V mains supply and has a predicted efficiency of 94%. A tower-like construction results in a volume of 1 liter and a power density of 1.5 kW/liter (25 W/in3). The measured waveforms verify matrix operation and show that the SiC JFET cascode devices have turn-on switching times of 30 ns. Analysis shows that the SMC heat sink and EMI filter volume can be minimized to 0.14 liters if the switching frequency is reduced to 40 kHz.

Johann W. Kolar

Papers

A 4.6W/mm 2 power density 86% efficiency on-chip switched capacitor DC-DC converter in 32 nm SOI CMOS

Control method for Inductive Power Transfer with high partial-load efficiency and resonance tracking

Switching control strategy for full ZVS soft-switching operation of a Dual Active Bridge AC/DC converter

An Ultra-High-Speed, 500000 rpm, 1 kW Electrical Drive System

A 100 kHz SiC Sparse Matrix Converter