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 application of soft-switching concepts or Silicon Carbide (SiC) devices are two enabling technologies to further push the efficiency, power density or specific weight of power electronics converters. For an automotive application, such as a dc-dc converter that interconnects the high voltage battery or ultra-capacitor in a hybrid electrical vehicle (HEV) or a fuel cell vehicle (FCV) to the dc-link, costs and failure rate are likewise of importance. Due to increasing requirements on multiple of these converter characteristics the comprehensive multi-objective optimization of the entire converter system gains importance. Thereto, this paper proposes an optimization method to explore the limits of power density as a function of the switching frequency and the number of phases of non-isolated bi-directional multi-phase dc-dc converters operated with soft-switching and Silicon devices and hard-switched converters that take advantage of SiC devices. In addition, the optimization includes an algorithm to determine the chip size required for the semiconductor devices under consideration of the thermal characteristics and efficiency requirements. Based on detailed analytical volume, loss and cost models of the converter components as well as on measurements demonstrative results on the optimum converter designs are provided and evaluated comparatively for the different converter concepts.

Multi-objective optimization and comparative evaluation of Si soft-switched and SiC hard-switched automotive DC-DC converters

A semi-analytical modulation scheme to operate a single-phase, single-stage dual active bridge (DAB) AC-DC converter under full-operating-range zero voltage switching (ZVS) is proposed. The converter topology consists of a DAB DC-DC converter, receiving a rectified AC line voltage via a synchronous rectifier. ZVS modulation strategies previously proposed in literature are either based on current-based (CB) or energy-based (EB) ZVS analyses. The combined phase-shift, duty-cycle, and switching frequency modulation proposed in this paper relies on a novel, current-dependent charge-based (CDCB) ZVS analysis, taking into account the commutation charge of the (parasitic) switch capacitances as well as the time dependency of the commutation currents. Thereby, commutation inductance is shown to be an essential element in achieving full-operating-range ZVS. Experimental results obtained from a 3.7 kW bidirectional electric vehicle battery charger which interfaces a 400 V DC-bus with the 230 Vac, 50 Hz utility grid are given to validate the analysis and practical feasibility of the proposed strategy.

Charge-based ZVS soft switching analysis of a single-stage dual active bridge AC-DC converter

Switching devices based on SiC offer outstanding performance with respect to operating frequency, junction temperature and conduction losses and enable a significant improvement of the system performance. There, the cascode consisting of a MOSFET and a JFET additionally has the advantage of being a normally off device and offering a simple control via the gate of the MOSFET. Without dv/dt control, however, the transients with hard commutation reach values of up to 45kV/µs, which could lead to EMC problems and especially in drive systems to problems related to earth currents (bearing currents) due to parasitic capacitances. Therefore, new dυ/dt control methods for the SiC MOSFET/JFET cascode as well as measurement results are presented in this paper. Based on this new concepts the outstanding performance of the SiC devices can be fully utilised without impairing EMC.

Controllable dυ/dt behaviour of the SiC MOSFET/JFET cascode an alternative hard commutated switch for telecom applications

The design of electromagnetic (EM) interference filters for converter systems is usually based on measurements with a prototype during the final stages of the design process Predicting the conducted EM noise spectrum of a converter by simulation in an early stage has the potential to save time/cost and to investigate different noise reduction methods, which could, for example, influence the layout or the design of the control integrated circuit Therefore, the main sources of conducted differential-mode (DM) and common-mode (CM) noise of electronic ballasts for fluorescent lamps are identified in this paper For each source, the noise spectrum is calculated and a noise propagation model is presented The influence of the line impedance stabilizing network (LISN) and the test receiver is also included Based on the presented models, noise spectrums are calculated and validated by measurements

EMI Noise Prediction for Electronic Ballasts

Three-phase rectifier systems without connection of the neutral wire are characterized by the coupling of the phase input currents. Considering these couplings requires a transformation of the system equations into a static αβ-frame or into the rotating dq-reference frame where instead of the three coupled phase currents two independent current components are controlled. In this paper, it is shown that, despite of the existing cross-couplings, three independent phase current controllers can be used to control the system. Thereto, the cross coupling elements of the system transfer matrix have to fulfill some requirements which are derived using the Gershgorin theorem. The three-phase Δ-switch rectifier circuit is used for analysis and a detailed model of the rectifier system is derived where the cross couplings are visible. The model is subsequently used to evaluate the cross couplings and three independent current controllers are designed. Simulation and experimental results verify the control approach using three independent current controller for three-phase rectifier systems.

Johann W. Kolar

Papers

Multi-objective optimization and comparative evaluation of Si soft-switched and SiC hard-switched automotive DC-DC converters

Charge-based ZVS soft switching analysis of a single-stage dual active bridge AC-DC converter

Controllable dυ/dt behaviour of the SiC MOSFET/JFET cascode an alternative hard commutated switch for telecom applications

EMI Noise Prediction for Electronic Ballasts

Current Control of Three-Phase Rectifier Systems Using Three Independent Current Controllers