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

This paper introduces a new efficient high step-up dc-dc converter with a shared input path and dual series coupled inductors at the output. This converter is suitable for high power applications due to its shared input current that puts low current stresses on the low voltage side switches. The proposed converter uses active clamp circuits with a shared clamp capacitor for main switches. In addition to the active clamp circuit, the leakage energy is recycled to the output by the act of an integrated regenerative snubber. Both active and passive switching devices operate with soft-switching performance i.e. Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS). Principle of operation and mathematical derivation are presented and verified through simulation and experimental results of a 1kW prototype.

A new soft-switched high step-up DC-DC converter with dual coupled inductors

/pdf/proceedings-of-the-ieee-energy-conversion-congress-and-2xxjk6v44s.pdf

Proceedings of the IEEE Energy Conversion Congress and Exposition, ECCE 2013

In this paper, conventional power system reliability and risk indices are employed to evaluate the reliability of a Power Electronic based Power System (PEPS) utilizing Physics of Failure (PoF) based reliability functions. Mission profile based methods have presented to estimate the failure probability of converters which implies non-constant failure rates for converters during operating period. Hence, a piece-wise solution is proposed to employ the Markov chain approach in order to evaluate the system level reliability of the PEPS with the non-constant failure rates. Furthermore, the impact of power management and thermal sharing on the system level reliability are studied. Numerical analyses and experiments are provided to validate the proposed approaches.

/pdf/reliability-and-risk-assessment-in-a-power-electronic-based-5dh7datlwp.pdf

Reliability and Risk Assessment in a Power Electronic Based Power System (PEPS): Using Non-Constant Failure Rates of Converters

Output voltage deviation is a key performance index of voltage regulator modules (VRMs) with consecutive load transients. Usually, a large-capacity filter capacitor bank is used in VRMs to reduce the voltage deviation and stabilize the output voltage during transients. However, capacitors are one of the most vulnerable links in power electronic converters. For reliability reasons, it is essential to reduce the capacitance requirement while guaranteeing the transient performances of VRMs. Focusing on this, many efforts have been made to optimize the design of VRMs, where the transient auxiliary circuit-based scheme is a popular one. Unfortunately, there exists a large number of additional components in the existing auxiliary circuits. Considering this issue, in this article, we present a virtual series voltage source (VSVS) based auxiliary circuit scheme, which has minimum component counts. By using a controlled coupled inductor as the VSVS, the proposed scheme enables VRMs to have a relatively small transient voltage overshoot and without needing large bulk capacitance. Moreover, considering different control schemes with the same designing aim, the number and the electrothermal stress of critical components (e.g., capacitors) of VRMs are different; it is difficult to compare directly their advantages and disadvantages. Regarding this issue, this article investigates the converter-level reliability of VRMs with different control schemes. Taking a 12–3.3 V VRM as a case study, the reliability benchmarking results illustrate that the proposed scheme can significantly improve the reliability of VRMs.

/pdf/reliability-improvement-of-voltage-regulator-modules-by-a-36cx1y8x.pdf

Reliability Improvement of Voltage Regulator Modules by a Virtual Series Voltage Source

This paper presents a new soft-switched, current-driven full-bridge converter. A simple snubber is used in order to get ZVS for all the main switches. The soft-switching realization is independent of the load. The snubber is placed in parallel with the bridge. All the resonant circuit energy is recycled by the load in each half cycle. No additional current stresses appear on the main switches. A design-oriented steady-state analysis leads to the expressions of the dc voltage conversion ratio and ZVS analytical conditions, allowing for a trade-off design of the resonant inductor. A prototype has been built with a high energy transfer efficiency. The simulation and experiment results confirm the detailed theoretical analysis.

Huai Wang

Papers

A new soft-switched high step-up DC-DC converter with dual coupled inductors

Proceedings of the IEEE Energy Conversion Congress and Exposition, ECCE 2013

Reliability and Risk Assessment in a Power Electronic Based Power System (PEPS): Using Non-Constant Failure Rates of Converters

Reliability Improvement of Voltage Regulator Modules by a Virtual Series Voltage Source

A new ZVS-PWM current-fed full-bridge converter with full soft-switching load range