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

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

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

Power electronics

Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

/pdf/light-emitting-diodes-ubzde6g9qc.pdf

Light-emitting diodes

Magnetic components are usually assumed relatively reliable in power electronic converters. Nevertheless, with the trend for ever-increasing power density, planar magnetics may need to be designed with reduced margins in terms of thermal and insulation. Wear out or even failure of magnetic components may become an issue in extreme design and operation scenarios. This paper presents the first observations in degradation testing of planar magnetics at high temperatures. It serves to investigate the change of various parameters and identify possible ones as the health indicators of magnetic components for power electronic applications. The degradation testing and characterization results are presented and interpreted.

/pdf/first-observations-in-degradation-testing-of-planar-1h3i9xcom4.pdf

First Observations in Degradation Testing of Planar Magnetics

The efficiency of 98% has been reported on transformer-less photovoltaic (PV) inverters and the penetration of grid-connected PV systems is booming as well. In the future, the PV systems are expected to contribute to the grid stability by means of low voltage ride-through operation and grid support. At the same time, the target of a long service time (25 years or more) imposes new challenges to grid-connected transformer-less PV systems. Achieving more reliable PV inverters is of intense interest in recent research. As one of the most critical stresses that induce failures, the thermal stresses on the power devices of a single-phase full-bridge PV inverter are analyzed in different operational modes in this paper. The low voltage grid condition is specially taken into account in this paper. The analysis is demonstrated by a 3 kW single-phase full-bridge grid-connected PV system by simulations. The mean junction temperature and the junction temperature fluctuation of the power devices can be reduced by properly injecting reactive current into the grid under grid faults, and consequently, the overall lifetime of the entire PV system is improved.

/pdf/thermal-optimized-operation-of-the-single-phase-full-bridge-1mzza9zhxa.pdf

Thermal Optimized Operation of the Single-Phase Full-Bridge PV Inverter under Low Voltage Ride-Through Mode

Power converters enable efficient and flexible control and conversion of electric energy among different smart grid players (ie producers, energy storage systems, and loads) One of the expected features of smart grid is that it will be more reliable compared to conventional grid However, power converters are one kind of the lifetime limiting components applied in smart grid One of the major causes is the malfunction of electrolytic capacitors (E-Caps) which are widely used for stabilizing the dc-link voltage in various types of power converters applied in smart grid A dc-link module is therefore proposed in this paper with a reduced value of dc-link capacitor and a series voltage compensator It allows the replacement of the popularly used E-Caps with alternatives of longer lifetime, like power film capacitors The basic concept, implementation and operation principle of the dc-link module are given The theoretical analysis is verified by simulation and experimental results (6 pages)

/pdf/long-lifetime-dc-link-voltage-stabilization-module-for-smart-44jxs6jdno.pdf

Long Lifetime DC-Link Voltage Stabilization Module for Smart Grid Application

This paper investigates the electromagnetic interference (EMI) emission in three-level active neutral-point-clamped (3L-ANPC) silicon carbide (SiC) inverter. Four typical modulation schemes of 3L-ANPC inverter are considered. An EMI model is established by including all the system parasitics and noise sources. Based on this model, a comparison of different modulation schemes on EMI emission is carried out. Simulations are performed in a case study to confirm the theoretical expectations.

/pdf/emi-modeling-of-three-level-active-neutral-point-clamped-sic-26w2sifer6.pdf

EMI Modeling of Three-Level Active Neutral-Point-Clamped SiC Inverter Under Different Modulation Schemes

Since power converters are widely used in many applications and are one of the reliability-critical part in power electronic equipment, the technology of monitoring its healthy state has obtained many attentions in industry and academia. According to this, a new measurement circuit for monitoring the healthy state of the three phase inverter is proposed in this paper. Firstly, the principle of the proposed measurement circuit is described. Then, it is validated in a three phase inverter and the experimental results agree well with theoretical analysis.

Huai Wang

Papers

First Observations in Degradation Testing of Planar Magnetics

Thermal Optimized Operation of the Single-Phase Full-Bridge PV Inverter under Low Voltage Ride-Through Mode

Long Lifetime DC-Link Voltage Stabilization Module for Smart Grid Application

EMI Modeling of Three-Level Active Neutral-Point-Clamped SiC Inverter Under Different Modulation Schemes

A Condition Monitoring Method for Three Phase Inverter Based on System-Level Signal